CHAPTER
INTRODUCTION TO CHAPTER 3—WIRING METHODS AND MATERIALS Chapter 3 covers wiring methods and materiais, and provides some very specific instaliation requirements for conductors, cables, boxes, raceways, and fittings. This chapter includes detailed information about the instaliation and restrictions involved with wiring methods. It may be because of that detail that many people incorrectly appiy the rules from this chapter. Be sure to pay careful attention to the details, and be sure that you make your instaliation in compliance with the rules in the Code, not just in the manner that you may have been taught or because "it's always been done that way." This is especially true when it comes to appiying the Tables. Violations of the rules for wiring methods found in Chapter 3 can result in problems with power quality and can lead to fire, shock, and other hazards. The type of wiring method you'll use depends on several factors: Job specifications, Code requirements, the environment, need, and cost are among them. Chapter 3 begins with rules that are common to most wiring methods [Article 300], it then covers conductors [Article 310], and enclosures [Articles 312 and 314]. The articles that follow become more specific and deal more in-depth with individua! wiring methods such as specific types of cables [Articles 320 through 340] and varióos raceways [Articles 342 through 390]. The chapter winds up with Article 392, a support system, and the final articles [Articles 394 through 398] for open wiring. Notice as you read through the varióos wiring methods that the Code attempts to use similar subsection numbering for similar topics from one article to the next, using the same digits after the decimal point in the section number for the same topic. This makes it easier to lócate specific requirements in a particular article. For example, the rules for securing and supporting can be found in the section that ends with .30 of each article. In addition to this, you'll find a "uses permitted" and "uses not permitted" section in nearly every article. Wiring Method ArUctes •
Article 300—Wiring Methods. Article 300 contains the general requirements for all wiring methods included in the NEC, except for signaling and Communications systems, which are covered in Chapters 7 and 8.
•
Article 310—Conductors for General Wiring. This article contains the general requirements for conductors, such as insulation markings, ampacity ratings, and conductor use. Article 310 doesn't apply to conductors that are part of flexible cords, fixture wires, or conductors that are an integral part of equipment [90.6 and 300.1 (B)].
•
Article 312—Cabinets, Cutout Boxes, and Meter Socket Enclosures. Article 312 covers the instaliation and construction specifications for cabinets, cutout boxes, and meter socket enclosures.
•
Article 314—Outlet, Device, Pulí and Junction Boxes, Conduit Bodies, Fittings, and Handhole Enclosures. Instaliation requirements for outlet boxes, pulí and junction boxes, as well as conduit bodies, and handhole enclosures are contained in this article.
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Chapter 3
Wiring Methods and Materials
•
Cable Articles
USE), Service-entrance cable can be a single-conductor
Articles 320 through 340 address specific types of cables. !f you take
or a muíticonductor assembiy within an overall nonmetal-
the time to become familiar with the varióos types of cables, you'll: • •
lic covering. This cable is used primarily for services not
Understand what's available for doing the work.
over 600V, but is aiso permitted for feeders and branch
Recognize cable types that have special NEC require-
circuits.
ments. •
Article 33&—Service-Entrance Cable (Types SE and
•
Avoid buying cable that you can't install due to Code
Article 340—Underground Feeder and Branch-Circuít Cable (Type UF). Underground feeder cable is a mois-
requirements you can't meet with that particular wiring
ture-, fungus-, and corrosion-resistant cable suitable for
method.
direct burial in the earth, and it comes in sizes 14 AWG Here's a brief overview of each one: •
through 4/0 AWG [340.104]. Muíticonductor UF cable is covered in molded plástic that surrounds the insulated
Article 320—Armored Cable (Type AC). Armored cable
conductors.
is an assembiy of insulated conductors, 14 AWG through 1 AWG, individuaily wrapped with waxed paper. The
Raceway Articles
conductors are contained within a flexible spiral metal , (steel or aluminum) sheath that interlocks at the edges.
•
°
Articles 342 through 390 address specific types of raceways. Refer
Armored cable looks like flexible metal conduit. Many
to Article 100 for the definition of a raceway. If you take the time to
electricians cali this metal cable "BX®."
become familiar with the varióos types of raceways, you'll:
Article 330—Metal-Ciad Cable (Type MC). Metal-dad
•
cable endoses insulated conductors in a metal sheath
•
of either corrugated or smooth copper or aluminum tubing, or spiral interlocked steel or aluminum. The phys-
•
Avoid buying a raceway that you can't install due to NEC requirements you can't meet with that particular wiring
wiring method permitted in almost any location and for
method.
MC cable is the interlocking kind, which looks similar to armored cable or flexible metal conduit.
Here's a brief overview of each one: •
Article 342—Intermedíate Metal Conduit (Type IMC). Intermedíate metal conduit is a circular metal raceway
Article 334—Nonmetallic-Sheathed Cable (Type NM).
with the same outside diameter as rigid metal conduit.
Nonmetallic-sheathed cable endoses two, three, or four
The wall thickness of intermedíate metal conduit is less
insulated conductors, 14 AWG through 2 AWG, within a
than that of rigid metal conduit, so it's a greater interior
nonmetallic outer jacket. Because this cable is nonme-
cross-sectional área for holding conductors. Intermedíate
tallic, it contains a sepárate equipment grounding con-
metal conduit is lighter and less expensive than rigid
ductor. Nonmetallic-sheathed cable is a common wiring
metal conduit, but it's permitted in all the same locations
method used for residential and commercial branch cir-
as rigid metal conduit. Intermedíate metal conduit aiso
cuits. Many electricians cali this plastic-sheathed cable
uses a different steel alloy, which makes it stronger than
"Romex®." •
Recognize raceway types that have special Code requirements.
ical characteristics of Type MC cable make it a versatile
almost any application. The most commonly used Type
•
Understand what's available for doing the work.
rigid metal conduit, even though the walls are thinner.
Article 336—Powíer and Control Tray Cable (Type TC). Power and control tray cable is a factory assembiy of two or more insulated conductors under a nonmetallic sheath for instaliation in cable trays, in raceways, or supported by a messenger wire.
•
Article 344—Rigid Metal Conduit (Type RMC). Rigid metal conduit is similar to intermedíate metal conduit, except the wall thickness is greater, so it's a smaller interior cross-sectional área. Rigid metal conduit is heavier than intermedíate metal conduit and it's permitted to be installed in any location, just like intermedíate metal conduit.
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Wiring Methods and Materials
•
Article 348—Flexible
•
Chapter 3
Metal Conduit (Type FMC).
•
Flexible meta! conduit is a raceway of circular cross
Electrical nonmetallic tubing is a pliable, corrugated, circular raceway made of PVC. It's often called "Smurf Pipe"
strip of either steel or aluminum. It's commonly called
or "Smurf Tube," because it was available only in blue
"Greenfieid" or "Flex."
when it carne out and at the time the children's cartoon characters "The Smurfs," were popular. It's now available
Article 350—Liquidtight Flexible Metal Conduit (Type
of circular cross section with an outer liquidtight, non-
in múltiple colors such as red and yellow as well as blue. •
metallic, sunlight-resistant jacket over an inner flexible
Article 376—Metal Wireways. A metal wireway is a sheet metal trough with hinged or removable covers for
metal core, with associated couplings, connectors, and
housing and protecting electrical conductors and cable, in
fittings. It's listed for the instaliation of electric conduc-
which conductors are placed after the wireway has been
tors. Liquidtight flexible metal conduit is commonly called
installed as a complete system.
"Sealtite®" or simply "liquidtight." Liquidtight flexible metal conduit is of similar construction to flexible metal
•
Article
380—Multioutlet
Assemblies.
A
multiout-
let assembiy is a surface, flush, or freestanding raceway
conduit, but it has an outer thermoplastic covering.
designed to hold conductors and receptacles. It's assem-
Article 352—Rigid Polyvinyl Chioride Conduit (Type PVC). Rigid polyvinyl chioride conduit is a nonmetallic
bled in the fieId or at the factory. •
raceway of circular cross section with integral or associ-
Article 386—Surtace Metal Raceways. A surface metal raceway is a metallic raceway intended to be mounted
ated couplings, connectors, and fittings. It's listed for the
to the surface with associated accessories, in which con-
instaliation of electrical conductors, •
Tubing (ENT).
section made of a heücally wound, interlocl
LFMC). Liquidtight flexible metal conduit is a raceway
•
Article 362—Electrical Nonmetallic
ductors are placed after the raceway has been installed
Article 356—Liquidtight Flexible Nonmetallic Conduit (Type LFNC). Liquidtight flexible nonmetallic conduit is
as a complete system. •
a raceway of circular cross section with an outer liquid-
Article 388—Surface Nonmetallic Raceways. A surface nonmetallic raceway is intended to be surface
tight, nonmetallic, sunlight-resistant jacket over an inner
mounted with associated accessories. Conductors are
flexible core, with associated couplings, connectors, and
placed inside after the raceway has been installed as a
fittings. It's listed for the instaliation of electrical conduc-
complete system.
tors. LFNC is available in three types: -
Type LFNC-A (orange). A smooth seamiess inner core
Cable l^ay
and cover bonded together with reinforcement layers •
inserted between the core and covers. -
Type LFNC-B (gray). A smooth inner surface with inte-
Type LFNC-C (black). A corrugated interna! and externa! surface without integral reinforcement within the
Article
358—Electrical
support cables and raceways. A cable tray isn't a raceway; it's a support system for raceways, cables, and enclosures.
conduit wall. •
or assembiy of units or sections with associated fittings that form a structural system used to secureiy fasten or
gral reinforcement within the conduit wall. -
Article 392—Cable Trays. A cable tray system is a unit
Metallic
Tubing
(EMT).
Electrical metallic tubing is a nonthreaded thinwall raceway of circular cross section designed for the physical protection and routing of conductors and cables. Compared to rigid metal conduit and intermedíate metal conduit, electrical metallic tubing is relatively easy to bend, cut, and ream. EMT isn't threaded, so all connectors and couplings are of the threadless type. Today, It's available in a range of colors, such as red and blue.
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275
Notes
Mike HoiVs lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
ARTICLE
lIIiI Wiring Methods 301 INTRODUCTION TO ARTICLE 300—WIRING METHODS Article 300 contains the general requirements for ail wiring methods included in the NEC. However, the article doesn't appty to Communications systems, which are covered in Chapter 8, except when Article 300 is specifically referenced in Chapter 8. This article is primarily concerned with how to install, route, spiice, protect, and secure conductors and raceways. How well you conform to the requirements of Article 300 will generally be evident in the finished work, because many of the requirements tend to determine the appearance of the instaliation. Because of this, it's often easy to spot Article 300 problems if you're looking for Code violations. For example, you can easily see when someone runs an equipment grounding conductor outside a raceway instead of grouping all conductors of a circuit together, as required by 300.3(B). A good understanding of Article 300 will start you on the path to correctly installing the wiring methods included in Chapter 3. Be sure to carefully consider the accompanying illustrations, and refer to the definitions in Article 100 as needed.
PART L GENERAL
^^^^^^^W
integral Parts of Equipment
300.1 Scope. (A) Wiring Installations. Article 300 contains the general requirements for power and lighting wiring methods. Author's Comment: The requirements contained in Article 300 don't apply to the wiring methods for signaling and Communications systems, except where there is a specific reference in Chapter 7 or 8 to a rule in Article 300. • CATV, 820.3 • Class 2 and 3 Circuits, 725,3 • Communications Cables and Raceways, 800.133(A)t2) • FireAlarm Circuits, 760.3 (B) Integral Parts of Equipment. The requirements contained in
I
The r
I
applV
Figure 300-1
Article 300 don't apply to the internal parts of electrical equipment. Figure 300-1
Author's Comment: Industry practico is to describe raceways using inch sizes, such as y2 in., 2 in., and so on; however, the
(C) Trade Sizes. Designators for raceway trade sizes are given in
proper reference (2005 NEC change) is to use "Trade Size Vz''
Table 300.1 (C).
or "Trade Size 2." In this textbook we use the term "Trade Size."
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277
300.3
Wiring Methods
300.3 Conductors.
Conductors G r o u p e d Together 300.3(B)(1)
(A) Conductors. Single conductors must be installed within a Chapter 3 wiring method, such as a raceway, cable, or enclosure. Ex: Overhead conductors can be installed in accordance with 225.6. (B) Circuit Conductors Grouped Togetlier. All conductors of a circuit must be installed in the same raceway, cable, trench, cord, or cable tray, except as permitted by (1) through (4). Figure 300-2
í Conductors run in parallel must have all circuit conductors within the s a m e raceway, trench, or cable.
Circuit Conductors G r o u p e d Together 300.3(B) _
ve
COftynghl 2011. www klik«Hon com
Figure 300-3
Induced Currents ín Ferrous Metal Parts Hysteresis Heating
VIOLATION CopyngW 2011, « « . MiKeHoít eom
All conductors of a circuit must be installed in t h e same raceway, cable, trench, cord, or cable tray to minimize induction heating of metallic raceways and enclosures. and to maintain a low-impedance ground-fault current path.
Ferrous Metal (not a l u m i n u m )
/'•-, One Cycle - AC
wwwMlwHoaconi
Figure 300-2
(1) Paralleled Installations. Conductors installed in parallel in accordance with 310.10(H) must have all circuit conductors within the same raceway, cable tray, trench, or cable. Figure 300-3 Ex: Parallel conductors run underground can be installed in different raceways (Phase A in raceway 1, Phase B in raceway 2, and so
Ferrous metal (steel a n d iron) molecules align to the polarity of the magnetic field, a n d w h e n t h e field reverses, the molecules reverse their polarity. This back-and-forth alignment of the molecules heats up ferrous metal parts. Figure 300-4
forth) if, in arder to reduce or elimínate inductive heating, if the raceway is nonmetallic or nonmagnetic and the instaliation compiles with
(3) Nonferrous Wiring Methods. Circuit conductors can be installed
300.20(8). See 300.5(1} Ex Z
in different raceways (Phase A in raceway 1, Phase B in raceway 2, and so on) if, in order to reduce or elimínate inductive heating, the
Author's Comment: All conductors of a circuit must be
raceway is nonmetallic or nonmagnetic and the instaliation compiles
installed in the same raceway, cable, trench, cord, or cable tray
with 300.20(8). See 300.3(B)(1) and 300.5(1) Ex 2.
to minimize induction of the heating of ferrous metal raceways and enclosures, and to maintain a low-impedance ground-fault current path [250,4(A)(3)]. Figure 300-4 (2) Grounding and Bonding Conductors. Equipment grounding jumpers can be located outside of a flexible raceway if the bonding jumper is installed in accordance with 250.102(E)(2}. Figure 300-5
278
(C) Conductors of Different Systems. (1) Mixing. Power conductors of alternating-current and direct-current systems rated 600V or less can occupy the same raceway, cable, or enclosure if all conductors have an insulation voltage rating not less than the máximum circuit voltage. Figure 300-6
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Wiring Methods
Equipment Bonding J u m p e r Outside a Raceway 250.102(E) 12}
W h e r e an external bonding j u m p e r or conductor, or equipment bonding j u m p e r is installed, it must be routed with t h e raceway and can't e x c e e d 6 ñ i n length.
Mixing P o w e r a n d Control Conductors
V I O L A T I O N [725.136(A)] Control, signal, and Communications wiring must be separated from power and lighting circuits so the higher-voltage conductors don't accidentally energize them.
Figure 300-7
Figure 300-5
• Class circuit conductors can be installed with associated Mixing Conductors of Different S y s t e m s 300.3(C)(1)
power conductors [725.48(B)(1)] if all conductors have an insulation voltage rating not less than the máximum circuit voltage [300.3(C)(1)1. Figure 300-8
4 8 0 V Circuit 6 0 0 V Insulation Mixing Class 1 Conductors With Power Conductors - Associated Equipment 725.48(B)(1)
120V Circuit 6 0 0 V Insulation
Associated E q u i p m e n t Conductors of different systems can occupy the s a m e raceway, cable, or enclosure if the insulation voltage rating isn't less than t h e m á x i m u m circuit voltage.
Power Conductors Class 1 Control Circuit
Figure 300-6
Class 1 control circuits a n d p o w e r conductors associated with t h e s a m e e q u i p m e n t can o c c u p y the s a m e raceway.
Author's Comments: • Control, signal,
and Communications
wiring
must be
Cociyn8hl2011,*ww.Mi«ieHoltcom
separated from power and lighting circuits so the highervoltage conductors don't accidentally energize the control,
Figure 300-8
signal, or Communications wiring: Figure 300-7 -
CATV Coaxial Cable, 820,133(A)
-
Class 1, Class 2, and Class 3 Control Circuits, 725.48 and
[725.130{A) Ex 2] can be installed with associated power
725.136(A)
conductors [725.48(B)(1)] ií all conductors have an insulation
-
Communications Circuits, 800.133{A)(1)(c)
voltage rating not less than the máximum circuit voltage
-
FireAlarm Circuits, 760.136(A)
[300.3{C)(1)]. Figure 300-9
-
Instrumentation Tray Cable, 727.5
-
A Class 2 circuit that's been reclassified as a Ciass 1 circuit
Sound Circuits, 640.9(C)
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279
300.4
Wiring IVIethods
Class 2 and 3 Circuits Reclassified as Class 1 725.130(A) Ex 2
(A) Cables and Raceways Through Wood Members. When the following wiring methods are installed through wood members, they must comply with (1) and (2). Figure 300-11
Where a Class 2 or 3 circuit is reclassified as a Class 1 circuit, it can b e run in the s a m e raceway, cable, or enclosure with power conductors to functionally associated equipment [725.48(B)].
^^T:^
Class 2 Circuit Reclassified a s a Class 1 Circuit
•
Armored Cable, Article 320
•
Electrical Nonmetallic Tubing, Article 362
•
Flexible Metal Conduit, Article 348
•
Liquidtight Flexible Metal Conduit, Article 350
•
Liquidtight Flexible Nonmetallic Conduit, Article 356
•
Metal-Ciad Cable, Article 330
•
Nonmetallic-Sheathed Cable, Article 334
•
Service-Entrance Cable, Article 338
•
Underground Feeder and Branch-Circuit Cable, Article 340
Figure 300-9
Protection Against Physical D a m a g e R a c e w a y s a n d Cables T h r o u g h W o o d Members 300.4(A)
Note 2: PV system conductors, both direct current and alternating current, are permitted to be installed in the same raceways. outlet and junction boxes, or similar fittings with each other, but they must be kept entirely independent of all other non-PV system wiring [690.4(6)1. Figure 300-10
Bored Hote, [300.4(A)(1)] VÁ in.orMore No Steel Píate Required
Bored Hole, [300.4(A)(1 Less T h a n VÁ in. Steel Píate Required
Notch (if Permitted)~j [300.4(A)(2)] I Steel Píate Required : Armored Cable Electrical Nonmetallic Tubing Flexible Metal Conduit Liquidtight Flexible Conduit PV systeiTi conductors. both de and ac^ are perriiiUed_tg be installed in the s a m e raceways. outlet and junction ^ boxes. or similar fittings. but must be entirely independent of non-PV system wiring [690.4(8)].
Metal-Ciad Cable Nonmetallic-Sheathed Cable Sen/ice-Entrance Cable CopyngM 2011. www MAeHo* com
Figure 300-11
(1) Holes In Wood Members. Hotes through wood framing members for the above cables or raceways must be not less than VA in. from
Figure 300-10
the edge of the wood member. If the edge of the hole is less than VA in. from the edge, a '/e in. thick steel píate of sufficient length and
300.4 Protection Against Physical Damage. Con-
width must be installed to protect the wiring method from screws and
ductors, raceways, and cables must be protected against physical
nails.
damage [110.27(6)].
Ex 1: A steel piafe isn't required to protect rigid metal conduit, intermedíate metal conduit, PVC conduit, or electrical metallic tubing.
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Wiring IVIethods
300.4
Ex 2: A listed and marked steel píate less than /w in. thick that provides equal or better protection against nail or screw penetration is permitted. Figure 300-12
R a c e w a y s a n d Cables Through W o o d M e m b e r s Notches in W o o d 300.4(A)(2) Ex 2
Raceways and Cables T h r o u g h W o o d M e m b e r s Bored Holes 300.4(A)(1) Ex 2 A listed a n d marked steel píate less than 1/16th i n . thick can be used w h e r e raceways a n d cables are laid in w o o d notches.
TT ^ 1
V
(
\ 1
\
A listed a n d marked steel píate less than 1/16th i n . thick can be used w h e r e t h e IV4 in. space from the nearest edge can't be maintained.
Figure 300-13
(1) Nonmetallic-Sheathed Cable (NM). If Type NM cables pass through factory or field openings in metal framing members, the cable must be protected by listed bushings or listed grommets that cover all
Figure 300-12
metal edges. The protection fitting must be secureiy fastened in the opening before the instaliation of the cable. Figure 300-14
Author's Comment: Hardened steel piafes thinner than Vie in. have been tested and found to provide better protection from screw and nail penetration than the thicker plates.
Protection Against Physical D a m a g e Type N M Cable T h r o u g h Metal Framing M e m b e r s 300.4(B)(1)
(2) Notches in Wood Members. If notching of wood framing members for cables and raceways are permitted by the building code, a '/i6Ín. thick steel píate of sufficient length and width must be installed
Metal Studs
to protect the wiring method laid in these wood notches from screws and nails. iys. '
CAUTION: ^hen drilling or notching wood members, • be sure to check
with the building inspector
to
ensure you don't damage or weaken the structure and viólate the building code. Ex 1: A steel píate isn't required to protect rigid metal conduit, intermedíate metal conduit, PVC conduit, or electrical metallic tubing.
N M cable installed through metal f r a m i n g m e m b e r s must be protected by listed bushings or g r o m m e t s . Figure 300-14
Ex 2: A listed and marked steel píate less than /w in. thick that provides equal or better protection against nail or screw penetration is permitted. Figure 300-13
(2) Type NM Cable and Electrical Nonmetallic Tubing. If nails or screws are likely to penétrate Type NM cable or electrical nonmetallic
(B) Nonmetallic-Sheathed Cable and Electrical Nonmetallic Tubing
tubing, a steel sieeve, steel píate, or steel clip not less than '/e in. in
Through Metal Framing Members.
thickness must be installed to protect the cable or tubing.
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300.4
Wiring Methods
Ex: A listed and marked steel píate less than A in. thick that provides equal or better protection against nail or screw penetration is
Protection Against Physical D a m a g e Cables Parallel to Framing M e m b e r s and Furring Strips 300.4(D)
permitted.
Framing " Member
(C) Behind Suspended Ceilings. Wiring metliods, such as cables or raceways, installed behind paneis designed to allow access must be
Cable must be at Ieast I V i in. from the e d g e of a framing m e m b e r or furring strip, or be protected by a steel píate.
supported in accordance with its applicable article. Figure 300-15
Protection Against Physical D a m a g e Behind S u s p e n d e d Ceilings 300.4(C)
Suspended Ceiling
Wiring installed behind paneis designed to allow a c c e s s m u s t be supported in a c c o r d a n c e with its applicable article.
C o p y r i í * M11. «ww M Í I B U D U con.
Furring Strip
Framing Member
Figure 300-16
Author's Comment: This rule doesn't apply to control, signalCopyogW 3011. nwww MikeHo* com
ing, and Communications cables, but similar requirements are contained in Chapters 6.7, and 8 as follows:
Figure 300-15
• CATV Coaxial Cable, 820.24 • Communications Cable, 800.24
Author's Comment: This rule doesn't apply to control, signat, and Communications cables, but similar requirements are contained in Chapters 6, 7, and 8 as follows: • CATV Coaxial Cable. 820.21 and 820.24 • Communications Cable, 800.21 • Control and Signaling Cable, 725.21 and 725.24
• Control and Signaling Cable, 725.24 • Optical Fiber Cable, 770.24 • Fire Alarm Cable, 760.8 • Audio Cable, 640.6(B) Ex 1: Protection isn't required for rigid metal conduit, intermedíate metal conduit, PVC conduit, or electrical metallic tubing.
• Fire Alarm Cable, 760.7 and 760.8
Ex 2: For concealed work in finished buildings, or finished paneis for
• Optical Fiber Cable. 770.21 and 770.24
prefabricated buildings ifsuch supporting is impracticable, the cables
• Audio Cable, 640.6{B)
can be fished between access
(D) Cables and Raceways Parallel to Framing Members and
points.
Ex 3: A Usted and marked steel píate less than /le ¡n. thick that pro-
Furring Strips. Cables or raceways run parallel to framing members
vides equal or better protection against nail or screw penetration is
or furring strips must be protected if they're likely to be penetrated by
permitted.
nails or screws, by installing the wiring method so it isn't less than
(E) Wiring Under Roof Decking. Cables, raceways, and enclosures
VA in. from the nearest edge of the framing member or furring strip.
under metal-corrugated sheet roof decking must not be located
If the edge of the framing member or furring strip is less than 1 '/4 in.
within VÁ in. of the roof decking, measured from the lowest surface
away, a Vie in. thick steel píate of sufficient length and width must be
of the roof decking to the top of the cable, raceway. or box. In addi-
installed to protect the wiring method from screws and nails. Figure
tion, cables, raceways, and enclosures aren't permitted in concealed
300-16
locations of metal-corrugated sheet decking type roofíng.
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Wiring IVIethods
300.5
Note: Roof decking material will be installed or replaced after the initial raceway or cabling which may be penetrated by the screws or other mechanical devices designed to provide "hold down" strength of the waterproof membrane or roof insulating material. Ex: Spacing from roof decking doesn't apply to rigid metal conduit
Author's Comments: • If IMC or RMC conduit enters an enclosure without a connector, a bushing must be provided, regardiess of the conductor size [342.46 and 344.46]. • An insulated fitting isn't required for a grounding electrode.
and intermedíate metal conduit (F) Cables and Raceways Installed in Grooves. Cables and race-
Figure 300-18
ways installed in a groove must be protected by a '/le in. thick steel píate or sieeve, or by VA in. of free space. Protection Against Physical D a m a g e R a c e w a y Terminations 300.4(G)
Author's Comment: An example is Type NM cable installed in a groove cut into the Styrofoam-type insulation building block structure and then covered with wallboard. Ex 1: Protection isn't required if tfie cable is installed in rigid metal conduit, intermedíate metal conduit, PVC conduit, or electrical
metal-
lic tubing. Ex 2: A listed and marked steel píate less than /le in. thick that provides equal or better protection against nail or screw penetration is permitted. (G) Insulating Fittings. If raceways contain insulated circuit conduc-
A bushing isn't required for a grounding electrode c o n d u c t o r 1
tors 4 AWG and larger that enter an enclosure, the conductors must be protected from abrasión during and after instaliation by a fitting
Figure 300-18
identified to provide a smooth, rounded insulating surface, such as an insulating bushing. Figure 300-17 Ex: Insulating bushings aren't required if a raceway terminates in a threaded raceway entry that provides a smooth, rounded, or flared Protection of Insulated Circuit Conductors Identified Insulated Fittings 300.4(G)
Bushing Not Required
surface for the conductors. An example would be a meter hub fitting oraMeyer's
hub-type fitting.
(H) Structural Joints. A listed expansion/deflection fitting or other ANY Wire Size
means approved by the authority having jurisdiction must be used I M C - 342.46
4 AWG and L A R G E R
R M C - 344.46
where a raceway crosses a structural joint intended for expansión, contraction or deflection.
j
300.5 Underground Installations.
6 AWG and S M A L L E R
(A) Mínimum Burial Depths. When cables or raceways are installed 4 AWG and L A R G E R
underground, they musí have a minimum "cover" in accordance with EMT
6 AWG and S M A L L E R 4 AWG and L A R G E R 6 AWG and SMALLER
Table 300.5. Figure 300-19
P V C - 352.46 E N T - 362.46
Copyright 2011. uvww MikeHolt com
Figure 300-17
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300.5
Wiring IVIethods
Underground Installations - M i n i m u m Cover Depths Table 300.5 UF or U S E Cables or Conductors Street Driveway Parking Lot Driveways One - Two Family
RMC or IMC
Reskiential PVC not Encased 15A&20AGFCI in Concrete 120V Branch Ckts
24 in.
24 in.
24 in.
¡ 1 8 ín:
|l8ln.
Jl8in.
Solid Rock With not Less than 2in. of Concrete Raceway On>y All Other Applications
U n d e r g r o u n d Installations Signal a n d C o m m u n i c a t i o n s Cables
I24in.
t 12 in. o
cae
I Raceway Onty I |6in.
24 In.
18 in.
X 12 in.
T h e cover requirements contained in 300.5 apply t o signaling and Communications wiring.
Copynflhl 2011. •wwJ**«Ho«.cofn
Figure 300-19
Figure 300-20
Table 300.5 Minimum Cover Requirements in luches Buried Cables
Metal Raceway
Nonmetallic
0
0
0
Dweiling Unit
24/12'
6
18
IDweIling Unit Driveway
18/12'
6
18/12'
Under Roadway
24
24
24
Other Locations
24
6
18
Location Under Building
Raceway
(B) Wet Locations. The interior of enclosures or raceways installed in an underground instaliation are considered to be a wet location. Cables and insulated conductors installed in underground enclosures or raceways must be listed for use in wet locations according to 310.10(C). Spiices within an underground enclosure must be listed as suitable for wet locations [110.14(6)]. Figure 300-21
U n d e r g r o u n d Installations W e t Locations 300.5(B}
'Residential branch circuits rated 120Voriess with GFCI protection and máximum overcurrent protection of 20A. Note: This is a summary of the NEC 's Table 300.5. See the table in the NEC for full details.
Cables a n d insulated conductors installed in u n d e r g r o u n d raceways a n d enclosures must be listed a s suitable for w e t locations.
Note 1 to Table 300.5 defines "Cover" as the distance from the top of the underground cable or raceway to the top suríace ot finished grade. Figure 300-05 02 N1
Author's Comment: The cover requirements contained in 300.5 don't apply to the following signaling, Communications,
Spiices within a n u n d e r g r o u n d enclosure must be a p p r o v e d for w e t locations.
and other power-limited wiring systems: Figure 300-20 CowrtBM2011
• CATV, 90.3 • Class 2 and 3 Circuits, 725.3 • Communications Cables and Raceways, 90.3
Figure 300-21
• Fire Alarm Circuits, 760,3 • Optical Fiber Cables and Raceways, 770.3
284
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Wiring IVIethods
300.5
Author's Comment: The definition of a "Wet Location" as con-
Underground Installations Protection of Direct Buried Conductors and Cables 300.5(D)(1)
tained in Article 100, includes installations underground, in concrete slabs in direct contact with the earth, locations subject to saturation with water, and unprotected locations exposed to weather If raceways are installed in wet locations above grade, the interior of these raceways is aiso considered to be a wet location [300.9]. (C) Cables Under Buildings. Cables installed under a building must
Protection for a m i n i m u m of8ft above ground.
Protection isn't required t o extend more than 18 in. below grade and protection above ground must extend to a height not less than 8 ft. S e e Table 300.5, C o l u m n s 1 and 4 .
be installed in a raceway that extends past the outside walls of the CopyngN 2011. w*wJ*l(»Holi c ^ . -
building. Ex 2: Type MC Cable Usted for direct burial is permitted under a build-
V: 18 in. Cover'...I y : ' 18 in. Cover
ing without instaliation in a raceway [330.10(A)(5)]. Figure 300-22 Figure 300-23 Type r^C Cable Under Buildings 300.5(C)Ex2
(4) Enclosure or Raceway Damage. If direct-buried cables, enclosures, or raceways are subject to physical damage, the conductors must be installed in rigid metal conduit, intermedíate metal conduit,
\
or Schedule 80 PVC conduit.
1 1
j ^
^
^
(E) Underground Spiices and Taps. Direct-buried conductors or
1
^
cables can be spiiced or tapped underground without a spiice box [300.15(G)], if the spiice ortap is made in accordance with 110.14(6). Figure 300-24
Type ÍVIC cable listed for direct burial or concrete encasement is permitted under a building without instaliation in a raceway [330.10(A)f5)] a n d in w e t locations [330.10(AH11)].
U n d e r g r o u n d Spiices - Single Conductors 300.5(E)
Figure 300-22 ^ | y ^ Type U F o r U S E ^ ^ ^ ^ • ^ ^ Single C o n d u c t o r (D) Protecting Underground Cables and Conductors. Direct-buried conductors and cables such as Types MC, UF, and USE must be protected from damage in accordance with (1) through (4). (1) Emerging from Grade. Direct-buried cables or conductors that emerge from grade must be installed in an enclosure or raceway to protect against physical damage. Protection isn't required to extend more than 18 in. below grade, and protection above ground must extend to a height of not less than 8 ft. Rgure 300-23 (2) Conductors Entering Buildings. Conductors that enter a building
Single Type U F or U S E conductors can be spiiced u n d e r g r o u n d with a device that's listed for direct burial. Figure 300-24
must be protected to the point of entrance.
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300.5
Wiring Methods
U n d e r g r o u n d Installations Grouping of Conductors 300.5(1)
(F) Backfill. Backfill material for underground wiring must not damage the underground cable or raceway, or contribute to the corrosión of the metal raceway. Author's Comment: Large rocks, chunks of concrete, steel rods, mesh, and other sharp-edged objects must not be used
OKAY
for backfill material, because they can damage the underground conductors, cables, or raceways. (G) Raceway Seals. If moisture could enter a raceway and contact Vp
energized live parts, a seal must be installed at one or both ends of the raceway. Author's Comment: This is a common probiem for equipment
opQ'
f All conductors of the s a m e circuit, inciuding the equipment . grounding conductor, must be inside the same raceway or . . in cióse proximity to each other. See 300.3(B).
located downhill from the supply, or in underground equipment rooms. See 230.8 for service raceway seals and 300.7(A) for
Figure 300-25
different temperature área seals. Note: Hazardous explosive gases or vapors make It necessary to seal underground raceways that enter the building in accordance with 501.15.
Ex 2: Parallel circuit
conductors
installed
in accordance
with
310.10(H) of the same phase or neutral can be installed in underground PVC conduits, if inductive heating at raceway terminations is reduced by the use of aluminum locknuts and cutting a slot between
Author's Comment: It isn't the intent of this Note to imply that
the individual holes through which the conductors pass as required óy
sealing fittings of the types required in hazardous locations be
300.20(8). Figure 300-26
installed in unclassified locations, except as required in Chapter 5. This aiso doesn't imply that the sealing material provides a watertight seal, but only that it prevenís moisture from entering
Underground Installations Isolated Parallel Phases 300.5(1) Ex 2
the raceways. (H) Bushing. Raceways that termínate underground must have
Individual sets of paraliei circuit conductors can be installed in individual raceways if inductive heating can be reduced by compiying with 300.20{B).
a bushing or fitting at the end of the raceway to protect emerging cables or conductors. (I) Conductors Grouped Together. All conductors of the same circuit, inciuding the equipment grounding conductor, must be inside the same raceway, or in cióse proximity to each other. See 300.3(B).
A l u m i n u m Locknuts
Figure 300-25
Nonmetallic R a c e w a y or Cable with Nonmetallic Cover
Ex 1: Conductors can be installed in parallel in raceways, ductor cables, or direct-buried single-conductor
muíticon-
cables. Each raceway
or muíticonductor cable must contain all conductors of the same circuit inciuding the equipment grounding conductor Each
direct-bur-
ied single-conductor cable must be located in cióse proximity in the
Figure 300-26
trench to the other single conductor cables in the same parallel set of conductors, inciuding equipment grounding
conductors.
Author's Comment: Installing ungrounded and neutral conductors in different PVC conduits makes it easier to termínate larger parallel sets of conductors, but it will result in higher levéis oí electromagnetic fields (EMF).
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Wiring Methods
300.6
Protection Against Corrosión and Deterioration 300.6
(J) Earth Movement. Direct-buried conductors, cables, or raceways that are subject to movement by settiement or frost musí be arranged to prevent damage to conductors or equipment connected to the wiring. (K) DJrectJonal Bering. Cables or raceways installed using directional boring equipment must be approved by the authority having jurisdiction for this purpose. Author's Comment: Directional boring technology uses a directional drill, which is steered continuously from point "A" to point "B." When the drill head comes out of the earth at point "B," it's replaced with a back-reamer and the duct or raceway
Raceways, cable armor, boxes, elbows, fittings, and supports must be of materiais suitable for the environment in which they're to be installed.
being installed is attached to it. The size of the boring rig (hp, torque, and pull-back power) comes into play, along with the types of soil, in determining the type of raceways required. For
Figure 300-27
telecommunications work, múltiple poly innerducts are pulled in at one time. At major crossings, such as expressways, railroads, or rivers, outerduct may be installed to créate a permanent
(2) Organic Coatings on Boxes or Cabinets. Boxes or cabinets
sieeve for the innerducts.
having a system of organic coatings marked "Raintight," "Rainproof,"
"Innerduct" and "outerduct" are terms usually associated with optical fiber cable installations. while "unitduct" comes with factory installed conductors. All of these come in various sizes. Galvanized hgid metal conduit, Schedule 40 and Schedule 80 PVC, HDPE conduit and nonmetallic underground conduit with conductors (NUCC) are common wiring methods used with directional boring installations.
or "OutdoorType," can be installed outdoors. (3) In Concrete or in Direct Contact with the Earth. Ferrous metal raceways, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, nipples, fittings, supports, and support hardware can be installed in concrete or in direct contact with the earth, or in áreas subject to severe corrosive influences if made of material approved for the condition, or if provided with corrosión protection approved for
300.6 Protection Against Corrosión and Deterioration. Raceways, cable trays, cablebus, cable armor, boxes. cable
the condition. Author's Comment Galvanized steel electrical metallic tubing can
sheathing, cabinets, elbows, couplings, fittings, supports, and support
be installed in concrete at grade level and in direct contact with the
hardware must be suitable for the environment. Figure 300-27
earth, but supplementary corrosión protection is usually required
(A) Ferrous Metal Equipment. Ferrous metal raceways, enclosures, cables, cable trays, fittings, and support hardware must be protected against corrosión by a coating of listed corrosion-resistant material.
(UL White Book, Guide Information for Electrical Equipment, vmN. ul.com/regulators/2008_WhiteBook.pdf). Electrical metallic tubing can be installed in concrete above the ground floor slab generally without supplementary corrosión protection. Figure 300-28
Where conduit is threaded in the field, the threads must be coaíed with an approved eiectrically conductive, corrosion-resistant com-
(B) Aluminum Equipment. Aluminum raceways, cable trays, cable-
pound, such as coId zinc.
bus, cable armor, boxes, cable sheathing, cabinets, elbows, cou-
Author's Comment: Nonferrous metal raceways, such as aluminum rigid metal conduit, don't have to meet the provisions of this section.
plings, nipples, fittings, supports, and support hardware embedded or encased in concrete or in direct contact with the earth must be provided with supplementary corrosión protection.
(1) Protected from Corrosión Solely by Enamel. If ferrous metal parts are protected from corrosión solely by enamel, they must not be used outdoors or in wet locations as described in 300.6(D).
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Wiring Methods
Protection Against Corrosión Raceways in Concrete or Direct Contact with Earth r 300.6(A)(3) ^
(1) Exposed to Sunlight. If exposed to sunlight, the materiais must be listed or identified as sunlight resistant. (2) Chemical Exposure. If subject to exposure to Chemical solvents, vapors, spiashing, or immersion, materiais or coatings must either be inherently resistant to Chemicals based upon their listing, or be identi-
Galvanized EMT installed in concrete above a ground floor slab doesn't require supplemental corrosión protection. j Galvanized R M C and IMC are permitted in most locations without supplemental conrosion protection.
I
na
Galvanized E M T in a ground floor slab or in direct contact with the earth requires supplemental corrosión protection.
fied for the specific chemical. (D) Indoor Wet Locations. In portions of dairy processing facilities, laundries, canneries, and other indoor wet locations, and in locations where walls are frequently washed or where there are surfaces of absorbent materiais, such as damp paper or wood, the entire wihng system, where installed exposed, inciuding all boxes, fittings, raceways, and cables, must be mounted so there's at Ieast Va in. of airspace between it and the wall or supporting surface. Author's Comment: See the definitions of "Exposed" and "Location, Wet" in Article 100. Ex: Nonmetallic raceways, boxes, and fittings are permitted without
ñgure 300-28
the airspace on a concrete, masonry tile, or similar surface. (C) Nonmetallic Equipment. Nonmetallic raceways, cable trays, cablebus, boxes, cables with a nonmetallic outer jacket and internal metal armor or jacket, cable sheathing, cabinets, elbows, couplings, nipples, fittings, supports, and support hardware must be made of material identified for the condition, and must comply with (1) and (2). Figure 300-29
Protection Against Corrosión - Nonmetallic E q u i p m e n t 300.6(C) Where exposed t o sunlight, material must be listed or identified as sunlight resistant [300.6(C)(1)].
Note: Areas where acids and alkali Chemicals are handied and stored may present corrosive conditions, particularty when wet or damp. Severe corrosive conditions may aiso be present in portions of meatpacking plants, tanneries, glue houses, and some stables; in installations immediately adjacent to a seashore or swimming pool, spa, hot tub, and fountain áreas; in áreas where chemical deicers are used; and in storage celfars or rooms for hides, casings, fertilizer, sait, and bulk Chemicals.
300,7 Raceways Exposed to Different Temperaturas. (A) Sealing. If a raceway is subjected to different temperatures, and where condensation is known to be a probiem, the raceway must be filled with a material approved by the authority having jurisdiction that will prevent the circulation of warm air to a colder section of the raceway An explosionproof seal isn't required for this purpose. Figure 300-30 (B) Expansión Fittings. Raceways must be provided with expansión fittings where necessary to compénsate for thermai expansión and contraction. Figure 300-31
t Nonmetallic raceways, enclosures, cable jackets, fittings, supports, and other nonmetallic e q u i p m e n t must be made of material a p p r o v e d for the condition in which they're installed. Figure 300-29
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Wiring Methods
300.10
Raceways Exposed to Different Temperatures 300.7(A}
Not Pennitted in Raceways 300.Q Walk-In Freezer or Cooler
Putty or Duct-Seal in Raceway
1
>
Seal-Off Fitting Not Required
Electric Conductors or Cables
Violation
Copyngnt 2011. vnmv.MikeHiTl) com
Raceways must be sealed t o prevent the circulation o f warm air to a colder section of the raceway or sieeve. Figure 300-30
R a c e w a y s aren't permitted t o contain pipes or tubes for s t e a m , water, air, g a s , drainage, etc.
Figure 300-32
Not Permitted in R a c e w a y s Section 300.8
Expansión Fitting 300.7(B) Expansión Fitting
Okay O p e n i n g is not a r a c e w a y CcpyrighlZOlO ¥fwwMikeHollcom
Water
R a c e w a y s are for the exclusive use of electrical conductors a n d cables, a n d must not contain piping for s t e a m , water, air, g a s , drainage, etc. Figure 300-31
Figure 300-33
Note: Table 352.44 provides ttie expansión characteristics for PVC conduit. The expansión characteristics for metal raceways are determined by multipiying the valúes from Table 352.44 by 0.20, and the expansión characteristics for aluminum raceways are determined by multipiying the valúes from Table 352.44 by 0.40. Table 354.44 provides the expansión characteristics for reinforced thermosetting resin conduit (RTRC).
300.9 Raceways in Wet Locations Above Grade,
wet locations must be listed for use in wet locations according to 310.10{C). Figure 300-34
300.10 Electrical Continuity. Metal 300.8 Not Permitted in Raceways.
insu-
lated conductors and cables installed in raceways in aboveground
raceways, cables, boxes,
Raceways are designed
fittings, cabinets, and enclosures for conductors must be metallically
for the exclusive use of electrical conductors and cables, and aren't
joined together to form a continuous, low-impedance fault current
permitted to contain nonelectrical components, such as pipes or tubes
path capabie of carrying any fault current likely to be imposed on it
for steam, water, air, gas, drainage, and so forth. Figures 300-32 and
[110.10, 250.4(A)(3), and 250.122]. Figure 300-35
300-33
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300.11
Wiring Methods
Raceways in W e t Locations A b o v e G r a d e 300.9
Electrical Continuity - Short Sections of R a c e w a y s 300.10 Ex 1
VIOLATION N M cable isn't suitable for a wet location [334.12(B)(4)].
Short sections of r a c e w a y s used for support or protection of cables aren't required to be eiectrically continuous or c o n n e c t e d t o an e q u i p m e n t g r o u n d i n g conductor [250.86 Ex 2]
Insulated conductors and cables installed in raceways located in w e t locations must be listed for use in w e t locations. Copyright 2011. www MikeHoll com
Figure 300-34
Copyright 2011. www MMHoH coin
Figure 300-36 Electrical Continuity 300.10
300.11 Securing and Supporting.
Panel (A) Secured in Place. Raceways, cable assemblies, boxes, cabinets,
Outlet
and fittings must be secureiy fastened in place. The ceiling-support wires or ceiling grid must not be used to support raceways and cables (power, signaling, or Communications). However, independent support wires that are secured at both ends and provide secure support are Effective Ground-Fault Current Path
Ground Fault
permitted. Figure 300-37
All metal raceways, cables, enclosures, and fittings for conductors must be bonded together to form an effective ground-fault current path which is intended to facilítate the operation of the circuit overcurrent device.
Securing a n d Supporting Fire-Rated S u s p e n d e d Ceiling 300.11 (A) Ceiling support wires can't be used t o support power, signaling, or Communications raceways or cables.
Figure 300-35
Metal raceways and cable assemblies must be mechanically secured to boxes, fittings, cabinets, and other enclosures. Ex 1: Short lengths of metal raceways used for the support or protection of cables aren't required to be eiectrically continuous, ñor are they required to be connected to an equipment grounding
conductor
ofa type recognized in 250.118 [250.86 Ex 2 and 300.12 Ex]. Figure 300-36
Independent support wires secured at both e n d s that provide secure support are permitted. Copyrtghl 2011. W)ni.MÉ*Hot«ani
Figure 300-37
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Wiring Methods
300.11
Author's Comment: Outlet boxes [314.23(D)] and luminaires
Raceways Used for Support 300.11 (B)
can be secured to the suspended-ceiling grid if secureiy fas-
^
tened to the ceiling-framing members by mechanical means such as bolts, screws, or rivets, or by the use of clips or other
L_
securing means identified for use with the type of ceiling-framing member{s) used [410.36(B)]. (1) Fire-Rated Ceiling Assembiy. Electrical wiring within the cavity
VIOLATION
of a fire-rated floor-ceiling or roof-ceiling assembiy can be sup-
R a c e w a y s can't be used for the support of other raceways, cables, o r equipment.
ported by independent support wires attached to the ceiling assembiy. The independent support wires must be distinguishable from the suspended-ceiling support wires by color, tagging, or other effective means.
www MWeHoH m m
•.
(2) Nonfíre-Rated Ceiling Assembiy. Wiring in a nonfire-rated floorceiling or roof-ceiling assembiy can be supported by independent
•
»
»
'y.-*: '
Figure 300-39
support wires attached to the ceiling assembiy. The independent support wires must be distinguishable from the suspended-ceiling support wires by color, tagging. or other effective means. Figure 300-38
(2) Class 2 and 3 Circuits. Class 2 and 3 cable can be supported by the raceway that supplies power to the equipment controlled by the Class 2 or 3 circuit Figure 300-40
^
—
Securing and Supporting Nonfire-Rated S u s p e n d e d Ceiling 300.11 (A){2)
Ceiling support wires can't be used t o support power, signaling, or Communications raceways or cables.
R a c e w a y s U s e d for Support Class 2 a n d 3 C a b l e s 300.11(B)(2) Equipment controlled by a Class 2 circuit.
Cable supported by a ] raceway is permitted.
Independent support wires used for support can b e attached to the nonfire-rated assembiy. These support wires must be distinguishable by color, tagging. etc. Copyright » 1 1 . www.MiksHott.i
Figure 300-38
Class 2 cables can be supported by the raceway that supplies power to the equipment controlled by the cable. Figure 300-40
(B) Raceways Used for Support. Raceways must not be used as a means of support for other raceways, cables, or nonelectrical equipment, except as permitted in (1) through (3). Figure 300-39 (1) Identified. If the raceway or means of support is identified for the purpose.
(3) Boxes Supported by Raceways. Raceways are permitted as a means of support for threaded boxes and conduit bodies in accordance with 314.23(E) and (F), or to support luminaires in accordance with410.36(E). (C) Cables Not Used as Means of Support. Cables must not be used to support other cables, raceways, or nonelectrical equipment. Figure 300-41
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300.12
Wiring Methods
Mechanical Continuity 300.12 Ex 1 Cables Not Used a s M e a n s of Support 300.11 (C)
Violation
Furnace
Cables can't be used to support ottier cables, raceways, or nonelectrical equipment. CopyngWZOII. MHt.MIlHHakMm
Figure 300-41
300.12 Mechanical
Continuity.
Raceways and cable
sheaths must be mechanically continuous between boxes, cabinets,
Short sections of raceways used t o provide support or protection of cable from physical d a m a g e aren't required to be mechanically continuous.
and fittings. Figure 300-42 Figure 300-43 Mechanical Continuity 300.12 Mechanical Continuity O p e n - B o t t o m Equipment 300.12 Ex 2
R a c e w a y s a n d cable sheaths must be mechanically continuous b e t w e e n enclosures and fittings. B
OKAY
—
1
.
i
R a c e w a y s and cables installed into the bottom of openbottom equipment aren't required to be mechanically secured to the equipment.
Figure 300-42
Figure 300-44 Ex 1: Short sections of raceways used to provide support or protection of cable from physical damage aren't required to be mechanically
Author's Comment: When raceways are stubbed into an open-
continuous [250.86 Ex 2 and 300.10 Ex 1]. Figure 300-43
bottom switchboard, the raceway, inciuding the end fitting, can't rise more than 3 in. above the bottom of the switchboard enclo-
Ex 2: Raceways
at the bottom of open-bottom
as switchboards, motor control centers,
equipment,
and transformers,
such
sure [408.5].
aren't
required to be mechanically secured to the equipment. Figure 300-44
Mike Hoit's Iliustrated Guide to Understanding the 2011 National ElecMcal Code, Volume 1
Wiring IVIethods
300.13
300.13 Spiices and PIgtalls.
Author's Comment: Tfie opening of tlie ungrounded con-
A) Conductor Spiices. Spiices must be in enclosures as per 300.15 and aren't permitted in raceways, except as permitted by 376.56,
ductors, or tlie neutral conductor of a 2-wire circuit during the repiacement of a device, doesn't cause a safety hazard, so pigtaillng these conductors isn't required [110.14(B)].
386.56, or 388.56. Figure 300-45 CAUTION: If the continuity of the neutral conductor of a multiwire circuit is interrupted
(oponed), the
resultant over- or undervoltage can cause a fire and/ Spiices in R a c e w a y 300.13(A)
or destruction of electrical
Example:
equipment
A 3-wire, single-phase, 120/240V multiwire circuit
supplies a 1,200W, 120V hair dryer and a 600W, 120V televisión. Figure 300-47 If the neutral conductor of the multiwire circuit is interrupted, it will cause the 120V televisión to opérate at WOVand consume 1,067W of power (instead of 600W) for only a
fewseconds
before itburns up. Figure 300-48 Spiices or taps aren't permitted within a raceway. CopyogM 2011, www.Mik8HoK.eom
Step 1: Determine the resistance ofeach appliance, R = EVP. Rof the hair dryer = 120V2/1,200W R of the hair dryer = 12 ohms
Figure 300-45
R ofthe televisión = 120V2/600W R of the televisión = 24 ohms
(B) Conductor Continuity. Continuity of the neutral conductor of a
Step 2: Determine the current of the circuit, I = E/R.
multiwire branch circuit must not be interrupted by the removal of a
E=240V
wiring device. In these applications the neutral conductors must be
R = 36 ohms (12 ohms + 24 ohms)
spiiced together, and a pigtail must be provided for the wiring device.
l = 240V/36ohms
Figure 300-46
l^6.70A Step 3: Determine the operating voltage for each appliance, E = IxR. Conductor Continuity (Pigtail) Multiwire Circuit 300.13(B)
I = 6.70A R=12
ohms for hair dryer and 24 ohms for TV
Voltage of hair dryer ^ 6.70A x 12 ohms Voltage of hair dryer = 80V Multiwire
Circuit.
Pigtail Required for Neutral
Conductor Pigtail not Required
Voltage of televisión - 6.70A x 24 ohms Voltage of televisión = 160V
Continuity of the neutral conductor of a multiwire branch circuit must not be interrupted by the removal of a wiring device. Figure 300-46
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Wiring IVIethods
300.14
Danger of an O p e n Neutral on a Multiwire Circuit
Miswired Multiwire Circuit - Overload on Neutral V I O L A T I O N [210.4(B)]
Okay
i
20A + 15A = 35A L1
L1 L2 H.D. 12Í1
T2&1
" T "
^
^
\n = 3 5 A
600W TV
120V
TV 24Q:
, /
240V ,
V2
Vi !
120V I L2-*- _
j
1200W Hair Dryer
—
—
» Copynghl 2011, *w*.Mit
er Connection
Parallel Circuit Voltage Drop of Televisión = 120V Voltage Drop of Hair Dryer = 1 2 0 V
Caution: If the u n g r o u n d e d conductors o f a circuit aren't terminated to different phases the currents on the neutral conductor won't but will a d d , which can c a u s e a d a n g e r o u s on the neutral conductor.
multiwire or lines, cancel, overload
Figure 300-49
Figure 300-47
300.14 Length of Free Conductors.
Danger of an O p e n Neutral on a Multiwire Circuit
At ieast 6 in of free
conductor, measured trom the point in the box where the conductors enter the enclosure, must be left at each outlet, junction, and switch
Danger
point for spiices or terminations of luminaires or devices. Figure 300-50
L e n g t h of Free Conductor 300.14 240V
Series Circuit Open Neutral
Series Circuit Voltage Drop of Televisión = 160V
A m i n i m u m of 3 in. outside o f o p e n i n g is required.
Voltage Drop o f Hair Dryer = 8 0 V Copyngni 20)1. www.UkvHolLcom
Figure 300-48
WARNING: Failure to terminate the ungrounded conductors to sepárate phases
can cause the neutral
conductor to become overloaded, and the insulation can be damaged or destroyed by excessive
heat
Conductor
overheating is known to decrease the service Ufe of insulating materiais, which creates
Boxes with o p e n i n g s less than 8 in. must have at Ieast 6 in. of free conductor a n d at Ieast 3 in. of free conductor outside the box o p e n i n g . Figure 300-50
the potential for arcing faults in
hidden locations, and can ultimately lead to fires. It isn't known just how long conductor insulation lasts, but heat does
Boxes that have openings less than 8 in. in any dimensión, must have
decrease its Ufe span. Figure 300-49
at ieast 6 in. of free conductor, measured from the point where ttie conductors enter the box, and at Ieast 3 in. of free conductor outside the box opening. Figure 300-51
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Mike HoiVs iliustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Wiring Methods
300.15
Length of Free Conductor 300.14
Spiice and Termination Points 300.15 A box must b e installed at each spiice or termination point for power a n d lighting systems.
3 in. outside of opening is required.
At Ieast 6 in. of free conductor is required at each box. Where the box opening is less than 8 in., conductors must extend at Ieast 3 in. outside the box o p e n i n g . Figure 300-51
Figure 300-52
Author's Comment: Tiie following text was tiie Paneis' Spiice a n d Termination Points Conduit Body
Statement when it rejected my proposal to require the free conductor length to be unspiiced in the 2008 NEC. "The purpose of Section 300.14 is to permit access to the end of the conductor. Whether this conductor is spiiced or unspiiced does not affect the length of this free end of the conductor. Many conductors origínate inside the box and are spiiced to other conductors within the box but extend out of the box for connection to a device of some kind. Making this change would not permit this very common application. Even the exception to this section States that unspiiced or unterminated conductors do not have to
Conductors can b e spiiced in a conduit body [314.16(C)(2)].
comply with 300.14." Ex: Six inches of free conductor isn't required for conductors
that
pass tfirougfi a box wittiout a spiice or termination.
300.15 Boxes or Conduit Bodies.
Spiices aren't permitted in a short-radius conduit body [314.16(C)(2)].
A box must be installed
C o p r i a M 2011. *ww.M*«Holl,coni
Figure 300-53
at each spiice or termination point, except as permitted for: Figure 300-52
Author's Comment: Boxes aren't required for the following signaling and Communications cables or raceways: Figure 300-54
•
Cabinet or Cutout Boxes, 312.8
•
Conduit Bodies, 314.16(C) Figure 300-53
•
Luminaires, 410.64
•
Surface Raceways, 386.56 and 388.56
•
Wireways, 376.56
mke
• • CATV. 90.3
' ^
• Class 2 and 3 Control and Signaling, 725.3 • Communications, 90.3
. '
• Optical Fiber, 770.3
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295
300.15
Wiring IVIethods
Spiice and Termination Points Control, Signal, a n d Communications Circuits
(C) Raceways for Support or Protection. When a raceway is used for the support or protection of cables, a fitting to reduce the potential for abrasión must be placed at the location the cables enter the raceway. Figure 300-56
Reception A r e a
I \r R o o m
R a c e w a y s for Support or Protection 30Q.15{C) A bbox ( isn't required. W h e n a raceway is used for the support or protection of cables, a fitting to reduce the potential for abrasión must b e placed at the location the cables enter the raceway.
Copyrighl 2011. wwwMilmHoll.com
A box isn't required for Communications, signal, and control conductors [90.3, 725.3, and 770.3]. Figure 300-54
Fittings and Connectors. Fittings can only be used with the specific wiring methods for which they're listed and designed. For example, Type NM cable connectors must not be used with Type AC cable, and electrical metallic tubing fittings must not be used with rigid metal conduit or intermedíate metal conduit, unless listed for the purpose.
Figure 300-56
Figure 300-55 (F) Fitting. A fitting is permitted in lieu of a box or conduit body where conductors aren't spiiced or terminated within the fitting if it's accesFittings and Connectors 300.15
sible after instaliation. Figure 300-57
Fitting in Lieu o f Box 300.15{F)
272 E M T Connector
VIOLATION Fittings are permitted only on the wiring method f o r which they're listed.
\
A fitting is permitted in lieu of a box or conduit body w h e r e the conductors aren't spiiced or terminated within the fitting and the fitting is accessible after instaliation.
TA R M C Copynghl 2011. www.UiksHoiI com
Figure 300-55 Copyr>Qh12011 www M Í K B H O I I com
Author's Comment: PVC conduit couplings and connectors are permitted with eléctrica! nonmetallic tubing if the proper glue is
Figure 300-57
used in accordance with manufacturer's instructions [110.3(B)]. See 362.48.
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Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
300.17
Wiring Methods
(G) Underground Spiices. A box or conduit body isn't required where
Spiice and Termination Points Handhole Enclosure 300.15(L)
a spiice is made underground if the conductors are spiiced with a spiicing device listed for direct burial. See 110.14(B) and 300.5(E). Author's Comment: See the definition of "Conduit Body" in
A box isn't required for conductors in handhole enclosures. Spiices must comply with 314.30.
Article 100. ÉÉHlhhHíliWÉlWlÉf
{!) Enclosures. A box or conduit body isn't required where a spiice is made in a cabinet or in cutout boxes containing switches or overcurrent devices if the spiices or taps don't fill the wiring space at any crass section to more than 75 percent, and the wiring at any cross section doesn't exceed 40 percent. See 312.8 and 404.3(B). Figure 300-58
Figure 300-59 Spiice and Termination Points Switch/Circuit Breaker Enclosure 300.15(1)
300.16 Raceway or Cable to Open or Concealed Wiring. (B) Bushing. A bushing is permitted in lieu of a box or terminal where
An enclosure can be used as a raceway if the conductor fill doesn't exceed 4 0 % , a n d spiices are permitted if the fill doesn't exceed 7 5 % [312.8 a n d 404.3].
the conductors emerge from a raceway and enter or terminate at equipment such as open switchboards, unenclosed control equipment, or similar equipment.
300.17 Raceway Sizing.
Raceways must be large enough to
permit the instaliation and removal of conductors without damaging the conductor's insulation. Copynght 2011. *iww.M*oHcm com
Author's Comments: Figure 300-58
• When all conductors in a raceway are the same size and of the same insulation type, the number of conductors permitted
Author's Comment: See the definitions of "Cabinet" and "Cutout Box" in Article 100.
can be determined byAnnex C. • When different size conductors are installed in a raceway, conductor fill is limited to the percentages in Table 1 of
(L) Handhole Enclosures. A box or conduit body isn't required for
Chapter 9. Figure 300-60
conductors installed in a handhole enclosure. Spiices must be made
Table 1, Chapters
in accordance with 314.30. Figure 300-59 Author's Comment: Spiices or terminations within a handhole
Number
Percent Fill
must be accomplished by the use of fittings listed as suitable for
1 Conductor
53%
wet locations [110.14{B) and 314.30(C)].
2 Conductors
31%
3 or more
40%
The above percentages are based on conditions where the length of the conductor and number of raceway bends are within reasonable limits [Chapter 9, Table 1, Note 1].
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297
300.17
Wiring IVIethods
Raceway Fill LImitation Chapter 9, Table 1
C o n d u c t o r Cross-Sectional A r e a Chapter 9, Tables 5 and 8
One Conductor 5 3 % Fill
Raceway 24 i n . o r Less: 6 0 % Fill Note 4
Two Conductors 3 1 % Fill Cable is Treated a s 1 Conductor 5 3 % Fill, Note 9
OQD) Three o r More Conductors 4 0 % Fill
Cop/nght 2011. www WikeHoA com
W h e n conductors are installed in a raceway, conductor fill is limited to the above percentages. Figure 300-60
Table 5 10THHN (Solid/Stranded) Area 0.0211 in.2
Table 8 10 A W G Bare Solid Area 0.008 in.2
Table 8 10 A W G Bare Stranded Area 0.011 in.2
CopyfigM 2011. woMJMMHoa com
Figure 300-62
Question: How many 12 THHN conductors can be installed in R a c e w a y Cross-Sectional A r e a Chapter 9 - Table 4
trade size ^ electrical metallic tubing? Figure 300-61 (a) 12
(b) 13
(c) 14
(d)16
Answer: (d) 16 conductors [Annex C, Table C1]
Total A r e a 1 0 0 % 0.864 s q in.
Step 1: When sizing a raceway first determine the total área of conductors (Chapter 9, Table 5 for insulated conductors and Chapter 9, Table 8 for bare conductors). Figure 6 0 % Fill - | 0.519 sq i n .
300-62 Step 2: Select the raceway from Chapter 9, Table 4, in accordance with the percent fill listed in Chapter 9, Table 1. Figure 300-63 Copynghl 2011, www Mlk.Hnlt.eom
Raceway Sizing 300.17
Figure 300-63
Question: What trade size Schedule 40 PVC conduit is required for the following conductors? ?\gwe 300-64 %EMT
3—500 THHN 1—250 THHN 1 6 - 1 2 T H H N conductors [ A n n e x C, Table C.1]
When all conductors in a raceway are the s a m e size and insulation type, the number of conductors permitted can be determined by A n n e x C.
1—3 THHN (a) 2
(C)4
(06
Answer: (b) 3 continuedon
nextpage
Copynghl 2011. www MkeHoH com
Figure 300-61
298
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
300.19
Wiring IVIethods
Inserting Conductors in R a c e w a y Complete Runs 300.18(A)
Step 1: Determine ttie total área of conductors [Ctiapter9, Table 5]: 500 THHN
0.7073 x3=
2.1219 in.^
250 THHN
0.3970 X 1 -
0.3970 in.^
3 THHN
0.0973 X 1 -
+ 0.0973 in.^
Total Area =
VIOLATION R a c e w a y s must be complete prior to the instaliation of conductors.
2.6162 in.'
Step 2: Select the raceway at 40 percent fill [Chapter 9, Table 4]: Trade size 3 Schedule 40 PVC - 2907 sq in. of conductor fill at 40%.
Cap^hfú 2011. R a c e w a y Sizing 300.17
wwwi-MikaH
Figure 300-65
300.19 Supporting Conductors in Vertical Raceways. (A) Spacing Intervals. If the vertical rise of a raceway exceeds the Step 1. Determine the conductor área, Chapter 9, Table 5. 500 kcmil = 0.7073 i n . ^ x 3 conductors 250 kcmil = 0.3970 in.2 x 1 conductor 3 A W G = 0.0973 in.2 x 1 conductor Total área of the conductors
= = = =
2.1219 0.3970 0.0973 2.6162
in.^ in.^ in.^ in.^
valúes of Table 300.19(A), the conductors must be supported at the top, or as cióse to the top as practical. Intermedíate support must aiso be provided in increments that don't exceed the valúes of Table 300.19(A). Figure 300-66
Step 2. Size the raceway at 4 0 % fill, Chapter 9, Table 4 . Trade Size 3 P V C at 40 percent fill = 2.907 in.^
.^^Z:^'^
Figure 300-64
300.18 Inserting Conductors in Raceways. (A) Complete Runs. To protect conductor insulation from abrasión during instaliation, raceways must be mechanically completed behA/een the pulling points before conductors are installed. See 300.10 and 300.12. Figure 300-65 Ex: Short sections of raceways used for the protection of cables from physical damage aren't required to be installed complete
between
outlet, junction, or spiicing points. (B) Welding. Metal raceways must not be supported, terminated, or
Figure 300-66
connected by welding to the raceway
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299
Wiring IVIethods
300.20
Author's Comment: The weight of long vertical runs of conductors can cause the conductors to actually drop out of the
Magnetic materiais naturally resist the rapidly changing magnetic fields. The resulting friction produces its own additional
raceway if they aren't properiy secured. There have been many
heat—hysteresis heating—in addition to eddy current heating.
cases where conductors in a vertical raceway were released
A metal which offers high resistance is said to have high mag-
from the pulling "basl^et" or "grip" {at the top) without being
netic "permeability." Permeability can vary on a scale of 100 to
secured, and the conductors fell down and out of the raceway,
500 for magnetic materiais; nonmagnetic materiais have a per-
injuring those at the bottom of the instaliation.
meability of one. Simply put, the molecules of steel and iron align to the polarity of the magnetic field and when the magnetic field reverses,
300.20 Induced Currents In Ferrous Metal Enclosures and Raceways.
the molecules reverse their polarity as well. This bacl<-and-forth
(A) Conductors Grouped Together. To minimize induction heating
the current flows, the greater the heat rises in the ferrous metal
of ferrous metal raceways and ferrous metal enclosures for alternat-
parts. Figure 300-68
alignment of the molecules heats up the metal, and the more
ing-current circuits, and to maintain an effective ground-fault current path, all conductors of a circuit must be installed in the same Induced Currents in Ferrous Metal Parts Hysteresis Heating
raceway, cable, trench, cord, or cable tray. See 250.102(E), 300.3(B), Ferrous Metal (not a l u m i n u m )
300.5(1), and 392.8(0). Figure 300-67
O n e Cycle - AC
Induced Currents in Ferrous Metal Parts Conductors Grouped Together 300.20(A)
All conductors of a circuit must be installed in t h e s a m e raceway, cable, trench, cord, or cable tray to minimize induction heating of ferrous metal enclosures and r a c e w a y s .
Ferrous metal (steel a n d iron) molecules align to t h e polarity of the magnetic field, a n d w h e n the field reverses, the molecules reverse their polarity. This back-and-forth alignment of the molecules heats up ferrous metal parts. Figure 300-68
CopyngW 2011. www HfckeHoh com
When conductors of the same circuit are grouped together, the magnetic fields of the different conductors tend to cancel
Figure 300-67
each other out, resulting in a reduced magnetic field around the conductors. The lower magnetic field reduces induced currents
Author's Comment: When alternating current (ac) flows through a conductor, a pulsating or varying magnetic field is
in the ferrous metal raceways or enclosures, which reduces the hysteresis heating of the surrounding metal enclosure.
created around the conductor. This magnetic field is constantly expanding and contracting with the amplitude of the ac current. In the United States, the frequency is 60 cycles per second (Hz). Since ac reverses polarity 120 times per second, the magnetic
•
WARNING: There's press
on the effects
been much discussion of electromagnetic
in the
fields on
humans. According to the Instituto of Electrical and
field that surrounds the conductor aiso reverses its direction 120
Electronics
times per second. This expanding and collapsing magnetic field
at this time to define an unsafe electromagnetic field level.
Engineers
(IEEE), there's insufficient
information
induces eddy currents in the ferrous metal parts that surround the conductors, causing the metal parts to heat up from hysteresis heating.
300
Mike HoiVs iilustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
300.21
Wiring IVIethods
(B) Single Conductors. When single conductors are installed in nonmetallic raceways as permitted in 300.5(1) Ex 2, the inductive heat-
S p r e a d of Fire or Products of Combustión 300.21
ing of the metal enclosure must be minimized by the use of aluminum locknuts and by cutting a slot between the individual holes through which the conductors pass. Figure 300-69
Induced Currents in Metal Parts Single Conductors 300.20(B) 'PHASE^
V^ÍhASeN
Narrow Slot Cut Between Knockouts
O p e n i n g s into or through fire-rated assemblies must be firestopped using a p p r o v e d m e t h o d s to maintain the fire-resistance rating. ,
Bottom of Metal Enclosure Copyriom 2011, www MikeHon.com
Figure 300-70 (>ipyñSlW20ii,wi«v<.Mi*eHoitc«ii
Parallel conductors form a single conductor.
\
A l u m i n u m locknuts reduce hysteresis heating.
Author's Comment: Fire-stopping materiais are listed for the specific types of wiring methods and the construction of the assembiy that they penétrate.
When single conductors are installed in a nonmetallic raceway, inductive heating o f t h e metal enclosure can be minimized by cutting a slot between the individual holes through which the conductors pass. Figure 300-69
Note: Directories of electrical construction matenals published by qualified testing laboratories contain listing and instaliation restrictions necessary to maintain the fire-resistíve rating of assemblies. Outlet boxes must have a horizontal separation not less than 24 in. when installed ín a fire-rated assembiy, unless an outlet box is Usted for closer spacing or protected by fire-resistant "putty pads" in accordance with manufacturer's instructions. Figure 300-71
Note: Because aluminum is a nonmagnetic metal, aluminum parts don't heat up due to hysteresis heating. Author's Comment: Aluminum conduit, locknuts, and enclosures carry eddy currents, but because aluminum is nonferrous,
S p r e a d of Fire or Products of C o m b u s t i ó n 300.21 Note 16in.^ • 16 in.
it doesn't heat up [300.20(B) Note],
VIOLATION
Top View
24 in.
300.21 Spread of Fire or Products of Combustión. Electrical circuits and equipment must be installed in such a way
VIOLATION
that the spread of fire or products of combustión won't be substan-
7 1!
Top View
24 in.^
tially increased. Openings into or through fire-rated walls, floors, and ceilings for electrical equipment must be fire-stopped using meth-
OKAY
ods approved by the authority having jurisdiction to maintain the fireresistance rating of the fire-rated assembiy. Figure 300-70
2 4 in.
b p View CapyrtoH 20ia www.MkeHoUcom
Outlet boxes installed on opposite sides of a fire-rated assembiy must have a horizontal separation not less than 24 in. unless listed for closer spacing or protected by fire-resistant "putty pads." Figure 300-71
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301
Wiring Methods
300.22
Author's Comments:
(B) Ducts Specifically Fabricated for Environmental Air. If neces
• Boxes installed in fire-resistance-rated assemblies must be listed for the purpose. If steel boxes are used, they must be secured to the framing member, so cut-in type boxes aren't
sary for direct action upon, or sensing of, the contained air, Type MC cable that has a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexi-
permitted (UL White Book, Guide Information for Electrical
ble metallic tubing, intermedíate metal conduit, or rigid metal conduit
Equipment, www.ul,com/regulators/2008_WhiteBook.pdf).
without an overall nonmetallic covering can be installed in ducts spe-
• This rule aiso applies to control, signaling, and Communications cables or raceways.
cifically fabricated to transport environmental air. Flexible metal conduit in lengths not exceeding 4 ft can be used to connect physically adjustable equipment and devices within the fabricated duct.
-
CATV, 820.26
-
Communications, 800.26
-
Control and Signaling, 725.25
-
FireAlarm,760.3(A)
-
Optical Fiber, 770.26
-
Sound Systems, 640.3(A)
Equipment is only permitted within the duct specifically fabricated to transport environmental air if necessary for the direct action upon, or sensing of, the contained air. Equipment, devices, and/or illumination are only permitted to be installed in the duct if necessary to facilítate maintenance and repair. Figure 300-73
300.22 Wiring in Ducts Not for Air HandIing, Fabricated Ducts for Environmental Air, and Other Spaces For Environmental Air (Plenums), The provi-
Wiring in Ducts Specifically Fabricated for Environmental A i r 300.22(B)
sions of this section apply to the instaliation and uses of electrical wiring and equipment in ducts used for dust, loóse stock, or vapor removal; ducts specifically fabricated for environmental air, and spaces used for environmental air (plenums). (A) Ducts Used for Dust, Loóse Stock, or Vapor. Ducts that transport dust, loóse stock, or vapors must not have any wiring method installed within them. Figure 300-72
VIOLATION Ducts specifically fabricated to transport environmental air aren't permitted to contain any wiring unless necessary for direct action or sensing of the contained air.
Ducts Used for Dust, Loóse Stock, or Vapor 300.22(A)
C o p y r l ^ 2011.
www.UtoHoKxom
Figure 300-73
Ducts that transport dust, loóse stock, or vapors must not have any w i h n g method installed within t h e m .
(C) Other Spaces Used for Environmental Air (Plenums). This section applies to spaces used for air-handiing purposes, but not fabricated for environmental air-handIing purposes.
5S¿ O Figure 300-72
302
This requirement
doesn't apply to habitable rooms or áreas of buildings, the prime purpose of which isn't air handiing.
Copyright 2011.
www.hfikvHoK com
Note 1: The spaces above a suspended ceiling or below a raised floor used for environmental air are examples of the type of space to which this section applies. Figure 300-74 Note 2: The phrase "other space used for environmental air (plenum)" correlatas with the term "plenum" in NFPA 90A, Standard for tt\e Instaliation of Air-Conditioning and Ventilating Systems, and other mechanical codes where the ceiling cavity plenum is used for return air purposes, as well as some other air-handling spaces.
Mike Hoit's iliustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
300.22
Wiring Methods
Other Spaces Used for Environmental Air (Plenum) 300.22(0) Note 1
Author's Comments: • PVC conduit [Article 352], electrical nonmetallic tubing [Article
Air Handler
Environmental Air Space (Plenum) .
)
i i I ^-Suspended Ceiiing
,,
I I
permitted to be installed in spaces used for environmental air because they give off deadly toxic fumes when burned or
i i
i
Return A i r G r i l l ^ t t T
superheated. • Plenum-rated control, signaling, and Communications cables
The space above a dropped ceiling or below a raised floor, used for environmental air are examples of "other spaces used for environmental air (plenums)." Cop™MZ011,ww*.MiKeHoB.com
362], liquidtight flexible conduit, and nonmetallic cables aren't
RaíSCd FlOOr
\
\ ^
(not in ITE room) | ^
Environmental Air Space (Plenum)
and raceways are permitted in cavity plenum space: Figure 300-76
i
^
Figure 300-74
-
CATV, 820.179(A)
-
Communications, 800.21
-
Control and Signaling, 725.154(A)
-
FireAlarm, 760.7
-
Optical Fiber Cables and Raceways, 770.113(0)
-
Sound Systems, 640.9(C) and 725.154(A)
• Any wiring method suitable for the condition can be used in Author's Comment: For the purpose of this book, when
a space not used for environmental air-handling purposes.
the NEC references "other space used for environmental air
Figure 300-77
(plenum)," the term cavity plenum space' will be used. (1) Wiring Methods. Electrical metallic tubing, rigid metal conduit, intermedíate metal conduit, armored cable, metal-ciad cable with-
S p a c e Used for Environmental Air (Plenum) Wiring Methods Permitted 300.22(C)(1)
out a nonmetallic cover, and flexible metal conduit can be installed in cavity plenum space. If accessible, surface metal raceways or metal wireways with metal covers can be installed in cavity plenum space. Plenum
Figure 300-75 Suspended Ceiling
S
Spaces Used for Environmental Air ÍPIenum) Wiring Methods Permitted 300.22(C)(1) Environmental Air Space (Plenum)
m Wihng methods permitted in a space used for environmental air are:
Air Handler
• • • • t Plenum-rated control, signaling, and Communications cables are permitted in p l e n u m s p a c e : • C A T V , 820.179(A) • C o m m u n i c a t i o n s , 800.21 • Control and Signaling, 725.154(A) • F i r e A l a r m , 760.7 • Optical Fiber Cables and R a c e w a y s , 770.113(C) • S o u n d Systems, 640.9(C) and 725.154(A)
Figure 300-76
EMT Type A C Cable R M C Type M C Cable without N M cover IMC F M C Cop/DgOt 2011, w * w M.keHoll.coin
Figure 300-75
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300.23
Wiring Methods
Space Not Used for Environmental Air Wiring Methods Permitted 300.22(C)(1)
(3) Equipment. Electrical equipment with metal enclosures is permitted to be installed in cavity plenum space. Author's Comment: Examples of electrical equipment permitted in cavity plenum space would be air-handiers, junction boxes, dry-type transformers; however transformers must not be rated not over 50 kVA when located in hollow spaces
Air Handler
| i J A | Suspended l^^^^^^^eilin^^
[450.13(6)]. Figure 300-79 t Return k Air Space Used for Environmental Air (Plenum) - Equipment 300.22(Cm
1
A space not used for environmental air-handling purposes has no wiring method restrictions.
Environmental Air Space (Ptenum)
Copyright 2011. www MikaHoH.coni
Transformers rated over 50 k V A a r e not permitted in hollow spaces [450.13(B)].
Figure 300-77 Electrical equipment with metal enclosures is permitted in plenum space.
(2) Cable Tray Systems.
I
Suspended Ceiling
C o p y n ) ^ 1011. www UfteHoK cMn
(a) Metal Cable Tray Systems. Metal cable tray systems can be installed to support the wiring methods and equipment permitted by
Figure 300-79
this section. Figure 300-78
300.23 Paneis Designed to Allow Access. Wihng Metal Cable Tray Systems ín Other Spaces Used for Environmental Air (Plenum) 3Qa22fC)f2JfaJ
cables, and equipment installed behind paneis must be located so the paneis can be removed to give access to electrical equipment. Figure 300-80
i
Environmental Air Space (Plenum)
I
'i Cable Tray
Author's Comment: Access to equipment must not be hindered by an accumulation of cables that prevent the removal of suspended-ceiling panels. Control, signaling, and Communications cables must be located and supported so the suspended-ceiling
Metal cable trav systems are permitted in other spaces used for environmental air (plenums) to support wiring methods and cable types permitted in other spaces used for environmental air fplenums).
panels can be moved to provide access to electrical equipment. • CATV Coaxial Cable, 820.21 • Communications Cable, 800.21 • Control & Signaling Cable, 725.21 • Fire Alarm Cable, 760.7
C í i P í T ^ 2011. www.MikeHoH c o n
Figure 300-78
304
• Optical Fiber Cable, 770.21 • Audio Cable, 640.5
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
300.23
Wiring Methods
Panels Designed to A l l o w A c c e s s 300.23 ^
.
^
Equipment Behind Removable Panels Wiring a n d equipment behind panels designed to allow access must b e located so the panels c a n b e r e m o v e d to give access to equipment.
R e m o v a b l e Panel Copyright 2011. «iww MiKehtoll.com
Figure 300-80
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Conductors for General Wiring INTRODUCTION TO ARTICLE 310—CONDUCTORS FOR GENERAL WIRING This article contains the general requirements for conductors, such as insulation markings, ampacity ratings, and conditions of use. Article 310 doesn't apply to conductors that are part of flexible cords, fixture wires, or to conductors that are an integral part of equipment [90.7 and 300.1 (B)]. People often make errors in appiying the ampacity tables contained in Article 310. If you study the explanations carefully, you'll avoid common errors such as appiying Table 310.15(B)(17) when you should be appiying Table 310.15(B)(16). Why so many tables? Why does Table 310.15(B)(17) list the ampacity of 6 THHN as 105 amperes, yet Table 310.15(B)(16) lists the same conductor as having an ampacity of only 75 amperes? To answer that, go back to Article 100 and review the definition of ampacity. Notice the phrase "conditions of use." These tables set a máximum current valué at which premature failure of the conductor insulation shouldn't occur during normal use, under the conditions described in the tables. The designations THHN, THHW, RHH, and so on, are insulation types. Every type of insulation has a limit to how much heat it can withstand. When current flows through a conductor, it creates heat. How well the insulation around a conductor can dissipate that heat depends on factors such as whether that conductor is in free air or not. Think about what happens when you put on a sweater, a jacket, and then a coat—all at the same time. You heat up. Your skin can't dissipate heat with all that clothing on nearly as well as it dissipates heat in free air The same principal applies to conductors. Conductor insulation aiso fails with age. That's why we conduct cable testing and take other measures to predict failure and replace certain conductors (for example, feeders or critical equipment conductors) while they're still within design specifications. But conductor insulation failure takes decades under normal use—and it's a maintenance issue. However, if a conductor is torced to exceed the ampacity listed in the appropriate table, and as a result its design temperature is exceeded, insulation failure happens much more rapidly—often catastrophically. Consequently, exceeding the allowable ampacity of a conductor is a serióos safety issue.
PART I. GENERAL 310.1 Scope.
í ü Dry and Damp Locations. Insulated conductors typically used in dry and damp locations include THHN, THHW, THWN, or THWN-2.
Article 310 contains the general requirements for
conductors, such as insulation markings, ampacity ratings, and their
Author's Comment: Refer to Table 310.104 for a complete list
use. This article doesn't apply to conductors that are an integral part
of conductors that may be installed in dry or damp locations.
of equipment [90.7 and 300.1 (B)]. (C) Wet Locations. Insulated conductors typically used in wet locations include:
PART II. INSTALLATION 310.10 Uses Permitted.
Conductors described in 310.104 can
be used in any oí the wiring methods recognized in Chapter 3 as per-
(2) Types THHW, THWN, THWN-2, XHHW, or XHHW-2 Author's Comment: Refer to Table 310.104 for a complete list of conductors that may be installed in wet locations.
mitted in ms Code [110.8].
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310.10
(D)^Locations Exposed to Direct Sunlight. Insulated conductors and ^
cables exposed to the direct rays of the sun must be:
Conductors in Parallel Conductor Characteristics 310.10(H)(2)
(1) Listed as sunlight resistant or marked as being sunlight resistant. W h e n conductors are run in parallel, cun-ent must be evenly distributed a m o n g the individual parallel conductors by requiring all conductors of the parallel set to; • Be the s a m e length • Be m a d e of the s a m e matehal • H a v e the s a m e insulation • Terminate in the s a m e manner
Figure 310-1
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Figure 310-2
(1) Be the same length. (2) Consist of the same conductor material (copper/aluminum). (3) Be the same size in circular mil área (minimum 1/0 AWG). Figure 310-1
(4) Have the same type of insulation (like THHN). (5) Terminate in the same method (set screw versos compression).
Author's Comment: SE cable and the conductors contained in the cable are listed as sunlight resistant. However, according
Author's Comment: Conductors aren't required to have the
to the UL listing standard, the conductors contained in SE cable
same physical characteristics as those of another ungrounded or
aren't required to be marked as sunlight resistant.
neutral conductor to achieve balance.
(2) Covered with insulating material, such as tape or sieeving mate-
(3) Sepárate Raceways or Cables. Raceways or cables containing
riais that are listed as being sunlight resistant or marked as being
parallel conductors must have the same electrical characteristics and
sunlight resistant.
the same number of conductors. Figure 310-3
(G) Corrosive Conditions. Conductor insulation must be suitable for any substance to which it may be exposed that may have a detri-
Author's Comment: If one set of parallel conductors is installed in a metallic raceway and the other conductors are installed in
mental effect on the conductor's insulation, such as oil, groase, vapor,
PVC conduit, the conductors in the metallic raceway will have
gases, fumes, liquids, or other substances. See 110.11.
an increased opposition to current flow (impedance) as com-
(H) Conductors in Parallel.
pared to the conductors in the nonmetallic raceway. This results
(I) General. Ungrounded and neutral conductors can be connected in
conductors.
in an unbalanced distribution of current between the parallel
parallel, only in sizes 1/0 AWG and larger. @ Conductor Characteristics. When circuit conductors are installed
Parallel sets of conductors aren't required to have the same physical characteristics as those of another set to achieve balance.
in parallel, the conductors must be connected so that the current will be evenly distributed between the individual parallel conductors by requiring all circuit conductors within each parallel set to: Figure 310-2
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310.10
Conductors for General Wiring
Conductors in Parallel Sepárate Cables or R a c e w a y s 310.10(H}(3}
(4) Conductor Ampacity Adjustment. Each current-carrying conductor of a paralleled set of conductors must be counted as a currentcarrying conductor for the purpose of conductor ampacity adjustment, in accordance with Table 310.15{B)(3)(a). Figure 310-5
R a c e w a y s containing parallel conductors must have the s a m e electrical characteristics and t h e s a m e n u m b e r of conductors.
Conductors in Parallel Conductor A m p a c i t y Adjustment 310.10(H)(4)
Two Parallel Sets Six Current-Carrying Conductors (Seven if Neutral is Current-Carrying) Copyngni Z011.
M
Each current-carrying conductor of a paralleled set of conductors must be counted as a currentcarrying conductor.
Figure 310-3
Author's Comment: For example, a 400A feeder with a neutral load of 240A can be paralleled as follows: Figure 310-4
CopyngTnl 2011. www M«ieHo« cnm
• Phase A, Two—250 kcmil THHN aluminum, 100 ft • Phase B, Two—3/0 THHN copper, 104 ft
Figure 310-5
• Phase C, Two—3/0 THHN copper, 102 ft • Neutral,Two—1/0 THHN aluminum, 103 ft • Equipment Grounding Conductor, Two—3 AWG copper, 101 ft*
(5) Equipment Grounding Conductors. The equipment grounding conductors for circuits in parallel must be sized in accordance with
*The minimum 1/0 AWG requirement doesn't apply to equipment
250.122(F). Figure 310-6
grounding conductors [310.10(H)(5)].
Conductors in Parallel E q u i p m e n t Grounding Conductor 310.10{H)(5}
Conductors in Parallel - Sepárate Cables or Raceways 310.10(H)(3) Okay P/?ase/4Seí; 2- 250 kcmil AL, 100 ft long Pilase B Set: 2- 3/0 A W G C U , 1 0 4 f t l o n g Phase C Set: 2-3/0 AWG CU, 102ftlong Neutral Set: 2 - 1 / 0 A W G AL, 103 ft long Equipment Ground Set: 2 - 3 A W G C U , 101 f t l o n g
600A Protection
600A Protection
Parallel L Conductors
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For current to be evenly distributed between the individual parallel conductors, each conductor (within a parallel set) must be identical to each other.
T h e e q u i p m e n t grounding conductor in each raceway is sized to 250.122 b a s e d o n t h e rating of the overcurrent device. 6 0 0 A = 1 A W G Figure 310-6
Figure 310-4
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310.15
Author's Comment: The minimum 1/0 AWG paraliei conduc-
(2) Conductor Ampacity—Lower Rating. Where more than one
tor size rule of 310.10(H) doesn't apply to equipment grounding
ampacity applies for a given circuit length, the lowest valué must be
conductors.
used. Figure 310-8
(6) Equipment Bonding Jumpers. Equipment bonding jumpers are sized in accordance with 250.102.
Conductor Ampacity - Lower Rating 310.15(A)(2)
Author's Comment: The equipment bonding jumper isn't required to be larger than the largest ungrounded circuit conductors suppiying the equipment.
Higher A m p a c i t y on Wall 12 T H W N - 2 = 3 0 A
Lower A m p a c i t y o n Roof 12 T H W N - 2 = 17.40A ( 3 0 A x 0.58)
310.15 Conductor Ampacity. Author's Comment: According to Article 100, ampacity means the máximum current, in amperes, a conductor can carry continuously, where the temperature of the conductor won't be raised in excess of its insulation temperature rating. Figure W h e r e more than o n e ampacity rating applies to a single conductor length, the lower ampacity must be used for the entire circuit. Entire circuit is rated 17.40A.
310-7
g Article
Ampacity 100 Definition
Figure 310-8
3 T H W N - 2 Rated 115A at 90°C 115AX I.OOx 1.00 = 115A • 3 current-carrying conductors • Ambient Temperature 86°F
Ex: When different ampacities apply to a length of conductor, the higher ampacity is permitted ampacity length doesn't exceed
3 T H W N - 2 Rated 115A at 90*^C 115AX 0.87 X 0.80 = 80A
for the entire circuit if the reduced 10 ñ and its length doesn't
exceed
10 percent of the length of the higher ampacity. Figures 310-9 and 310-10
5 current-carrying conductors Ambient Temperature 110°F Conductor Ampacity Higher Rating 310.15(A)(2)Ex
The máximum current, in a m p e r e s , a conductor can carry continuously, under the conditions of use [310.15] without exceeding its temperature rating.
60 ft Figure 310-7
(A) General Requirements. (1) Tables for Engineering Supervisión. The ampacity of a conduc-
55 ft
Higher A m p a c i t y 8 A W G = Rated 55A at 90°C [TbI 310.15(B)(16)]
tor can be determined either by using the tables in accordance with 310.15(6), or under engineering supervisión as provided in 310.15(C). Note 1: Ampacities provided by this section don't take voltage drop into consideration. See 210.19(A) Note 4, for branch circuits and 215.2(0) Note 2, for feeders.
5ft
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; Lower Ampacity 4 ^ 8 A W G = 31.9A^ I (55AX0.58)
Entire Circuit Ampacity = 55A
T h e higher ampacity can be used if the length of the lower ampacity isn't more than 10 ft, a n d it isn't longer than 10 percent of the higher ampacity length. Figure 310-9
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310.15
Conductors for General Wiring
Conductor A m p a c i t y Correction and Adjustment 310.15(B) and Table 310.15(B)(16)
Conductor A m p a c i t y - Higher Rating 310.15(A)(2)Ex Higher Ampacity on Wall 8 THWN-2 = 55A
Lower A m p a c i t y o n Roof 8 T H W N - 2 = 31.90A {55A x 0.58)
. This raceway contains only 13 current-carrying conductors.
Table 310.15(B)(16) ampacity is based o n an ambient temperature of 86°F and no more than 3 current-carrying conductors bundied together. Conductor Ampacity Adjustment
The higher ampacity can be used if the length of the lower ampacity isn't more than 10 ft, a n d it isn't longer than 10 percent o f t h e higher ampacity length. Figure 310-10
Í
Ambient j¡£,^._^,jr* Temperature J f f W B ^ B l
If the ambient temperature is above 86°F or below 78°F, the conductor ampacity changes. [Table 310.15(B)(2)(a)]. Copynghl 201V www.MkeHott com
(3) Insulation Temperature LImitation. Conductors must not be
^
H
Conductor Conductor Bundiing
¿wWfTS^
If the n u m b e r of currentcarrying conductors exceeds 3, the conductor ampacity decreases [Table 310.15(B)í3j(a)].
Rgure 310-11
used where the operating temperature exceeds that designated for the type of insulated conductor involved. Note 1: The insulation temperature rating of a conductor [Table 310.104(A)] is the máximum temperature a conductor can withstand over a prolongad time period without serious degradation. The main factors to consider for conductor operating temperature include:
Conductor A m p a c i t y - Temperature Correction Adjustment 310.15(B)(2)(a) R a c e w a y o n roof with four 10 T H W N - 2 . T h e ambient temperature is 150°F (90°F + 60°F [310.15(B)(3)(c)].
(1) Ambient temperature may vary along the conductor length as well as from time to time [Table 310.15(B)(2)(a)].
rsi
(2) Heat generated internally in the conductor—load current flow. (3) The rate at which generated heat dissipates into the ambient médium. (4) Adjacent load-carrying conductors have the effect of raising the ambient temperature and impeding heat dissipation [Table
10 T H W N - 2 rated 40A, TbI 310.15(B)(16) at 90°C Ampacity = 4 0 A x 0.58 x 0.80 Ampacity = 18.56A üá-i .
310.15(B)(3)(a)].
.-.
Figure 310-12
Note 2: See 110.14(0(1) for the temperature limitation of terminations.
(2) Conductor Ampacity Ambient Temperature Correction. When
(B) Ampacity Table. The allowable conductor ampacities listed in
conductors are installed in an ambient temperature other than 78°F
Table 310.15(B)(16) are based on conditions where the ambient tem-
to 86°F, the ampacities listed in Table 310.15(B)(16) must be cor-
perature isn't over 86°F, and no more than three current-carrying
rected in accordance with the multipliers listed in Table 310.15(B)(2)
conductors are bundied together. Figure 310-11
M : Figure 310-13
The temperature correction and adjustment factors apply to the conductor ampacity, based on the temperature rating of the conductor insulation in accordance with Table 310.15(B)(16). Figure 310-12
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Conductors for General Wiring
310.15
Conductor Ampacity - Ambient Temperature 310.15(B)(2)(a}
Question: What's the corrected ampacity of 3/0 THHN/THWN conductors in a dry location if the ambient temperature is
3-12 THHN Rated 30A
108°F? (a) 173A
(b) 196A
(c)213A
241A
Answer: (b) 196A Conductor Ampacity [90X] = 225A Correction Factor [Table 310.(B)(2)(a)] = 0.87 Corrected Ampacity = 225A x 0.87 Corrected Ampacity = 196A Ambient Temperature
Ambient Temperature
Ambient Temperature
150OF m°C Table Ampacity Correction Factor = 58% (0.58)
860F (30OC) 90OC Table Ampacity Correction Factor = 100% (1.00)
50OF 90OC Table Ampacity Correction Factor = 115% (1.15)
30 Table amps x 0.58 Ampacity - 17.4A
30 Table amps x 1.00 Ampacity = 30A
30 Table a m p s x 1 1 5 Ampacity = 34,5A
108°F?
Ambient Temperature Ovar 860F. Ampacity is Lower
Ambient Temperature 86°F, Ampacity Remains the Same
Ambient Temperature Below 8 6 0 F , Ampacity is Higher
(a) 164A
Question:
What's the corrected ampacity of 3/0 THHN/THWN
conductors in a wet location if the ambient temperature is
(b) 196A
(c}213A
(d)241A
Answer: (a) 164A Figure 310-13
Conductor Ampacity [75X] = 200A Correction Factor [Table 310.(B)(2)(a)] = 0.82 Corrected Ampacity = 200A x 0.82
Tabla 310.15(B)(2)(a) Ambient Temperature Correction Ambient
Ambient
Temperature
Temperature
!F
Corrected Ampacity = 164A
!C
Correction Factor 75°C Conductors
Correction Factor 90°C Conductors
(a) Four or More Current-Carryíng Conductors in a Raceway or
50 or less
10 or less
1.20
1.15
Cable. Where four or more current-carrying power conductors are in
51-59T
11-15°C
1.15
1.12
60-68°F
16-20°C
1.11
1.08
69-77°F
21-25°C
1.05
1.04
78-86°F
26-30X
1.00
1,00
87-95T
31-35°C
0.94
0.96
96-104T
36-40°C
0.88
0.91
105-113°F
41-45°C
0.82
0.87
114-122°F
46-50°C
0.75
0.82
123-13rF
51-55X
0,67
0.76
132-140°F
56-60°C
0.58
0.71
141-149°F
61-65°C
0.47
0.65
150-158°F
66-70°C
0.33
159-167°F
71-75X
168-176T 177-185T
Conductor Ampacity Adjustment.
a raceway longer than 24 in. [310.15(B){3)(a)(3)], or where cables are bundied for a length longer than 24 in., the ampacity of each conductor must be reduced in accordance with Table 310.15(B)(3)(a).
Table 310.15(B)(3)(a) Conductor Ampacity Adjustment for More Than Three CurrentCarrying Conductors in a Raceway or Cable Number of Conductors'
Adjustment
4-6
0.80 or 80%
7-9
0.70 or 70%
10-20
0.50 or 50%
21-30
0.45 or 50%
0.58
31-40
0.40 or 40%
0.00
0.50
41 and above
0.35 or35%
76-80'^C
0.00
0.41
81-85°C
0,00
0.29
'Number of conductors is the total number of conductors in the raceway or cable adjusted in accordance with 310.15(B)(5) and (6).
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310.15
Conductors for General Wiring
Author's Comment: Conductor ampacity reduction is required wlien four or more current-carrying conductors are bundied
Conductor A m p a c i t y - A d j u s t m e n t Factor 310.15(B)(3)(a)(2)
because tieat generated by current flow is not able to dissipate as quickiy as three or fewer current-carry conductors, Figures 310-14 and 310-15
Conductor Ampacity A d j u s t m e n t Factor 310.15(B)(3)(a) No Ampacity Adjustment Three or Fewer Conductors
Ampacity Adjustment Factor = 7 0 % C o n d u c t o r ampacity adjustment of Table 310.15(B)(3)(a) d o not apply to conductors in raceways having a length not exceeding 2 4 in. Figure 310-16
(4} Conductor ampacity adjustment of Table 310.15(B)(3)(a) does not Conductors have more surface área for heat dissipation. Copyright 2011, www MikeHo«.com
Bundied conductors have heat held in by other conductors.
Figure 310-14
apply to conductors within Type AC or Type MC cable under the following conditions: Figure 310-17
Conductor A m p a c i t y - Table 310.15{B)(16) A d j u s t m e n t Factor - A C and M C Cables 310.15(B)(3)(a)(4) Conductor A m p a c i t y A d j u s t m e n t Factor 310.15(B)(3)(a) and Table 310.15(B)(16)
Ampacity adjustment doesn't apply to Type AC or MC cable when: (a) Cable has no outer jacket. fb) Each cable has no more than three current-carrying conductors. fe) The conductors are 12 AWG copper (d) No more than 20 current-carrying conductors are installed without maintaining spacing for a continuous length longer than 24 in.
Raceway contains 4 current-carrying conductors. T h e Table 310.15(B)(3)(a) adjustment factor is 0.80.
If more than 20 current-carrying conductors are bundied, a 60% ampacity adjustment factor applies.
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12 THWN-2 rated 30A, TbI 310.15(B)(16) at 90°C Ampacity = 3 0 A x 0.80 [Table 310.15(B)(3)(a)] Ampacity = 24A Figure 310-15
Figure 310-17
(a) The cables don't have an outer jacket, (b) Each cable has no more than three current-carrying conductors,
(1) Conductor ampacity adjustment of Table 310.15(B)(3)(a) does not apply to conductors installed in cable trays, 392.80 apply. (2) Conductor ampacity adjustment of Table 310.15(B)(3)(a) does not apply to conductors in raceways having a length not exceeding
(c) The conductors are 12 AWG copper, and (d) No more than 20 current-carrying conductors (ten 2-wire cables or six 3-wire cables) are installed without maintaining spacing for a continuous length longer than 24 in.
24 in. Figure 310-16
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310.15
(5) Ampacity adjustment of 60 percent applies to conductors within Type AC or Type MC cable without an overall outer jacket under the following conditions: (fa) The number of current-carrying conductors exceeds 20.
Circular R a c e w a y s Exposed to Sunlight on Roofs A m b i e n t Temperature Adjustments 310.15(B)(3}(c) Ambient The raceway is 3 / 4 in. above Temperature the roof, so a d d 4 0 O F to the
is 9 0 ° F
ambient temperature. (c) The cables are stacked or bundied longer than 24 in. without 8 THWN-2 Ampacity?
spacing being maintained. (c) Circular Raceways Exposed to Sunlight on Rooftops. When appiying ampacity adjustment correction factors, the ambient temperature adjustment contained in Table 310.15{B)(3)(c) is added to the outdoor ambient temperature for conductors installed in circular raceways exposed to direct sunlight on or above rooftops to determine the applicable ambient temperature for ampacity correction factors in Table 310.15(B)(2)(a) or Table 310.15(B)(2)(b). Figures 310-18 and 310-19
Table 310.15(B)(16) ampacity, 8 T H W N - 2 = 55A Adjusted Temperature: 90OF + 40OF [Table 310.15{B)(3}(c)] = 130OF Temp Con-ection Factor = 0.76 [Table 310.15{B)(2)(a)] N e w A m p a c i t y = 5 5 A x 0.76 = 41.80A Figure 310-19
Table 310.15(B)(3)(c) Ambient Temperature Adder for Raceways On or Above Rooftops
Circular Raceways Exposed to Sunlight on Roofs Ambient Temperature Adjustments 310.15(Bm(c)
Distance of Raceway Above Roof
Ambient Temperature is 90°F
C°
F°
33
60
22
40
Above 3y2¡n.to12in.
17
30
Above 12 in.to 36 in.
14
25
0 to y? in. ' The raceway is 3/4 in. above the roof, so add 40OF to the , ambient temperature.
Above Copyright 2011. " w * MIkoHon Com
Table 310.15{B)(16) ampacity. 6 T H W N - 2 = 75A Adjusted Temperature: 90°F + 40OF [Table 310.15(B)(3}(c)] = 130°F Temp Correction Factor = 0.76 [Table 310.15(B)(2)(a)] New Ampacity = 7 5 A x 0.76 = 5 7 A
in. to 3/2 in.
Author's Comment: This rule requires the ambient temperature used for ampacity correction to be adjusted where conductors or cables are installed in a circular raceway on or above a rooftop and the raceway is exposed to direct sunlight. The reasoning
Figure 310-18
is that the air inside circular raceways in direct sunlight is significantly hotter than the surrounding air, and appropriate ampacity corrections must be made in order to comply with
Note 1: See the ASHRAE Handbook—Fundamentáis (www.ashrae. org) as a source for the average ambient temperatures in various locations. Note 2: The temperature adders in Table 310.15(B)(3)(c) are based on the results of averaging the ambient temperatures.
310.10. (5) Neutral Conductors. (a) The neutral conductor of a 3-wire, single-phase, 120/240V system, or 4-wire, three-phase, 120/208V or 277/480V wye-connected system, isn't considered a current-carrying conductor for conductor ampacity adjustment of 310.15(B)(3)(a). Figure 310-20
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310.15
Conductors for General Wiring
Neutral Conductors From the S a m e Circuit 310.15(B)(5)(a)
(c) The neutral conductor of a 4-wire, three-phase, 120/208\ or 277/480V wye-connected system is considered a current-carrying conductor for conductor ampacity adjustment of 310.15(B)(3)
120/240V
(a) if more than 50 percent of the neutral load consista of nonlinearloads.Figure310-22 15A
ih5A
Neutral Conductor of a W y e 4-Wire Circuit Suppiying Nonlinear Loads 310.15(B)(5)(c) Cop/ngtil 2011. www MikeHon.coni
100A Nonlinear
Neutral conductors that carry only unbalanced current from other conductors f r o m the s a m e circuit aren't considered current-carrying conductors. Figure 310-20
(b) The neutral conductor of a 3-wire circuit from a 4-wire, threephase, 120/208V or 277/480V wye-connected system is considered a current-carrying conductor for conductor ampacity adjustment of 310.15(B)(3)(a). Author's Comment: When a 3-wire circuit is supplied from a
O d d triplen harmonio currents from nonlinear loads a d d o n t h e neutral conductor a n d the actual current can be twice the u n g r o u n d e d conductor's current. Figure 310-22
4-wire. three-phase, 120/208V or 277/480V wye-connected system, the neutral conductor carries approximately the same current as the ungrounded conductors. Figure 310-21
Author's Comment: Nonlinear loads supplied by a 4-wire, three-phase, 120/208V or 277/480V wye-connected system can produce unwanted and potentially hazardous odd triplen harmonio currents (3rd, 9th, 15th, and so on) that can add on
Neutral Conductor of a 3-Wire Circuit From a W y e 4-Wire System 310.15(B)(5)(b) 120/208V or 277/480V
the neutral conductor. To prevent fire or equipment damage
Current-Carrying Conductor
visit www.MikeHolt.com, click on the "Tecbnical" link, then the
from excessive harmonio neutral current, the designer should consider increasing the size of the neutral conductor or installing a sepárate neutral for each phase. For more information, "Power Quality" link. Aiso see 210.4(A} Note, 220.61 Note 2,
T h e neutral conductor o f a 3-wire circuit from a 4-wire, w y e system is considered a current-carrying conductor.
and 450.3 Note 2. (6) Grounding Conductors. Grounding and bonding conductors aren't considered current carrying. Figure 310-23
Determine the neutral current. I NEUTRAL =
(7) Dweiling Unit Feeder/Service Conductors. For individual dweilJ{L2^
+
L32)
-
(L2
X
L3)
I NEUTRAL = 7 (1002 + 10Ó2y- 0 0 0 XIOO^ I NEUTRAL = 1 OOA
ing units of one-family, two-family, and multifamily dweilings, Table 310.15(B)(7) can be used to size 3-wire, single-phase, 120/240V service conductors. Figure 310-24
Figure 310-21
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310.15
Conductor Ampacity - Grounding a n d B o n d i n g Conductors 310.15(B)(6)
Service/Feeder Conductor Sizing for 120/240V Dweiling Unit 310.15(B)(7) Service conductors for more than one dweiling unit must be sized using Table 310.15(B)(16).
Copvrtghl»1l,w«M.KHi*Hall.com
Equipment grounding and bonding conductors aren't current-carrying and aren't counted w l i e n appiying the provisions of Table 310.15(B)(3)(a).
Feeder a n d service conductors for a n individual dweiling c a n b e sized using Table 310.15(B)(7). Figure 310-25
Figure 310-23
Service/Feeder Conductor Sizing f o r 120/240V Dweiling Unit 310.15(B)(7)
Neutral Conductor Sizing. For individual dweiling units of one-family, two-family, and multifamily dweilings, Table 310.15(B)(7) can be used to size the neutral conductor of a 3-wire, single-phase, 120/240V service or feeder that carries all loads associated with the dweiling unit, based on the calculated load in accordance with 220.61.
2 3 5 A Calculated Load 4/0 A W G Service a n d Feeder Conductors
CAUTION: Because the service neutral conductor is Wt^
required to serve as the effective ground-fault current path, it must be sized so it can safety carry the
máximum fault current likely to be imposed on it [ 110.10 and 250.4(A)(5)]. This is accomplished For individual dweiling units of one-family, two-family, and multifamily dweiling units, Table 310.15(B)(7) c a n be used to size 3-wire, single-phase, 120/240V service or feeder conductors that supply all loads that are part of, or associated with, the dweiling unit. Figure 310-24
by sizing the neutral con-
ductor In accordance with Table 250.66, based on the área of the largest ungrounded service conductor
[250.24(C)(1)].
Question: What size service conductors are required if the calculated load for a dweiling unit equals 195A, and the máximum unbalanced neutral load is 10OA ? Figure 310-26
|
Author's Comment: Table 310.15{B)(7) can't be used for service conductors for two-family or multifamily dweiling buildings.
(a) 1/0AWGand6AWG
(b) 2/0 AWG and 4 AWG
Figure 310-25
(c) 3/0AWG and 2AWG
(d) 4/0AWG and 1 AWG
Feeder conductors for individual dweiling units aren't required to be sized larger than service conductors sized to 310.15(B)(7} [215.2(A)
Answer: (b) 2/0 AWG and 4 AWG
|
Service Conductor: 2/0AWG rated 200A ¡Table 31015(B)(7)] Neutral Conductor: 4 AWG is rated 100A in accordance with Table 3W.15(B}(7).
in addition. 250.24(C) requires the neutral
conductor to be sized no smaller than 4 AWG based on 2/0AWG service conductors in accordance with Table 250.66.
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315
Conductors for General Wiring
310.106
Conductor Properties - 6 0 0 V or Less 310.104
S t r a n d e d Conductors 310.106(C)
Thermoplastic
1Í7
HH = (two H ) 90OC Insulation
I " Nylon Jacket or E q u i v a l e n !
—
Rubber
— H = (one H) 750C Insulation f
W e t Locations
Table 310.104(A) contains conductor insulation information, such as operating temperature and applications. T h e s e conductors can be used in a n y Chapter 3 wiring m e t h o d . Figure 310-28
Conductor sizes 8 A W G a n d larger must be stranded w h e n installed in a raceway. CopyrigM 2011, ww*.Mik^ton.com
Figure 310-30
Author's Comment: Solid conductors are often used for the
Conductor Properties - 6 0 0 V or Less 310.104
grounding electrode conductor [250.62] and for the bonding of pools, spas, and outdoor hot tubs [680.26(C)]. Technically, the
Thermoplastic
practice of installing 8 AWG and larger solid conductors in a
H = (one H ) 750C Insulation
raceway for the protection of grounding and bonding conductors is a violation of this rule.
i 2 90°C in Wet/Dry Locations
(D) Insulated. Conductors must be insulated except where specific permission allows them to be covered or bare. Figure 310-31
Nylon Jacket or Equivalent W e t Locations Conductors - Insulated
Table 310.104(A) contains conductor insulation information, such as operating temperature and applications. These conductors can be used in any Chapter 3 wiring m e t h o d . Copyright 20^1. www.MiRoHotl.com
Figure 310-29
310.106 Conductors (A) Minimum Size Conductors. The smallest conductor permitted for branch circuits for residential, commercial, and industrial locations is 14 AWG copper, except as permitted elsewhere in this Code. Author's Comment: There's a misconception that 12 AWG copper is the smallest conductor permitted for commercial or industrial facilities. Although this isn't true based on A/fC rules, it may be a local code requirement.
Figure 310-31
(C) Stranded Conductors. Conductors 8 AWG and larger must be stranded when installed in a raceway. Figure 310-30
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Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Conductors for General Wiring
310.110
Author's Comment: Equipment grounding conductors are per-
U n g r o u n d e d Conductor Identification 310.110(0)
mitted ío be bare, see 250.118(1). Figure 310-32
U n g r o u n d e d conductors must be clearly distinguishable from neutral a n d equipment grounding conductors.
Types of Equipment Grounding Conductors 250.118 An equipment g r o u n d i n g conductor can be any o n e or a combination of the types listed in 250.118. Conductors can be solid, stranded, bare, insulated, or covered.
FMC limited) LFMC limited)
Figure 310-33
N M Cable MC Cable (Amrior Not Listed as EGC)
Cable (Annor A C Listed as EGC) Cable
Author's Comments: • If the premises wiring system has branch circuits or feed-
Figure 310-32
ers supplied from more than one nominal voltage system, each ungrounded conductor of the branch circuit or feeder, if accessible, must be identified by system. The means of
310.110 Conductor Identification. (A) Grounded Conductor. Grounded conductors must be identified in accordance with 200.6. (B) Equipment Grounding Conductor. Equipment grounding conduc-
Identification can be by sepárate color coding. marking tape, tagging, or other means approved by the authority having jurisdiction. Such Identification must be permanently posted at each panelboard [210.5(C) and 215.12]. • The NEC doesn't require color coding of ungrounded con-
tors must be identified in accordance with 250.119.
ductors, except for the high-ieg conductor when a neutral
(C) Ungrounded Conductors. Ungrounded conductors must be
conductor is present [110.15 and 230.56]. Although not
clearly distinguishable from neutral and equipment grounding conductors. Figure 310-33
required, electricians often use the following color system for power and lighting conductor Identification: -120/240V, single-phase—black, red, and white -120/208V, three-phase—black, red, blue, and white -120/240V, three-phase, delta-connected system—black, orange, blue, and white -277/480V, three-phase, wye-connected system—brown, orange, yellow, and gray; or, brown, purple, yellow, and gray
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319
ARTICLE
312
Cabinets, Cutout Boxes, and Meter Socl
INTRODUCTION TO ARTICLE 312--CABINETS, CUTOUT BOXES, AND METER SOCKET ENCLOSURES This article addresses the instaliation and construction specifications for the Items mentioned in its title. In Article 310, we observed that the conditions of use have an effect on the ampacity of a conductor. Likewise, the conditions of use have an effect on the selection and application of cabinets, cutout boxes, and meter socket enclosures. For example, you can't use just any enclosure in a wet location or in a hazardous location. The conditions of use impose special requirements for these situations. For all such enclosures, certain requirements apply—-regardiess of the use. For example, you must cover any openings, protect conductors from abrasión, and allow sufficient bending room for conductors. Notice that Article 408 covers switchboards and panelboards, with primary emphasis on the interior, or "guts" while the cabinet that would be used to endose a panelboard is covered here in Article 312. Therefore you'll find that some important considerations such as wire-bending space at termináis of panelboards are included in this article. Article 312 covers the instaliation and construction specifications for cabinets, cutout boxes. and meter socket enclosures. [312.1]. Author's Comment: A cabinet is an enclosure for either surface mounting or flush mounting and provided with a frame in which a door may be hung. A cutout box is designed for surface mounting with a swinging door [Article 100]. The industry ñame for a meter socket enclosure is "meter can."
312.1
Scope. Article 312 covers the instaliation and construc-
tion specifications for cabinets, cutout boxes, and meter socket enclosures. Figure 312-1
Cabinets, Cutout B o x e s , and Meter C a n s 312.1 Screw/Bolt C o v e r Meter Socket Hinged Cover Enclosure
Author's Comment: A cabinet is an enclosure for either surface mounting or flush mounting and provided with a frame in which a door may be hung, A cutout box is designed for surface mounting with a swinging door [Article 100]. The industry ñame for a meter socket enclosure is "meter can." Panelboard Cabinet: Enclosure for Circuit Breakers
lIopyngM 2011. www KMi.Hall com
Cutout Box: Enclosure for Fuses
Meter Cans; Enclosure for Meter
Figure 312-1
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Mike HoiVs Iliustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
312.5
Cabinets, Cutout Boxes, and Meter Socket Enclosure
PART I. INSTALLATION
312.5 Enclosures.
312.2 Damp or Wet Locations.
(A) Unused Openings. Openings intended to provide entry for conductors must be adequately closed. Figure 312-3
Enclosures in damp or wet locations must prevent moisture or water from entering or accumulating wittiin the enclosure, and must be weatherproof. When the enclosure is surface mounted in a wet location, the enclosure must be mounted with not less than a
U n u s e d R a c e w a y and Cable Openings 312.5(A)
in. air
space between it and the mounting surface. See 300.6(D). If raceways or cables enter above the level of uninsulated live parts of an enclosure in a wet location, a fitting listed for wet locations must be used for termination. Author's Comment: A fitting listed for use in a wet location with a sealing locknut is suitable for this application, £x; The Va in. air space isn 't required for nonmetaiiic equipment, raceways, or cables.
312.3 installed in Walls.
Cabinets or cutout boxes installed
in walls of concrete, tile, or other noncombustible material must be
U n u s e d cable or r a c e w a y o p e n i n g s must be closed with a fitting that provides equivalent protection. Figure 312-3
installed so that the front edge of the enclosure is set back no more than Va in. from the finished surface. In walls constructed of wood or other combustible material, cabinets or cutout boxes must be flush
Author's Comment: Unused openings for circuit breakers must
with the finished surface or project outward.
be closed by means that provide protection substantially equivalent to the wall of the enclosure [408.7]. Figure 312-4
312.4 Repairing Gaps.
Gaps around cabinets and cutout
boxes that are recessed in noncombustible surfaces (plaster, drywail, or plasterboard) having a flush-type cover, must be repaired so that there will be no gap more than /a in. at the edge of the cabinet or cutout box. Figure 312-2
U n u s e d openings for circuit breakers a n d I switches must be closed using identified closures o r other a p p r o v e d m e a n s . Figure 312-4 Gaps around recessed cabinets and cutout boxes must be repaired s o there are no gaps greater than 1/8th in. Figure 312-2
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312.6
Cabinets, Cutout Boxes, and IVIeter Socket Enclosure
Cable Termination N o t Required 312.5(0) Ex
(C) Cable Termination. Cables must be secured to the enclosure with fittings designed and listed for the cable. See 300.12 and 300.15. Figure 312-5
N M cables can be sieeved if the: a. Cable is fastened within 1 ft. b. R a c e w a y doesn't penétrate a structural ceiling. c. Fittings are at the e n d of the raceway. d . R a c e w a y is sealed a n d fastened in place. e. Cable sheath is 74 in. inside. f. R a c e w a y is secured. g. C o n d u c t o r fill is limited to 60%.
Min. 18 in. Max. lOft
Cable Termination 312.5(0)
SurfaceMounted Panel
Cables must be secured to the enclosure with fittings d e s i g n e d and listed for the cable.
Co()yngM2011. www.MkeHon com
Figure 312-6
312.6 Deflection of Conductors.
Enclosures for conductors
must be sized to allow conductors to be deflected in accordance with Figure 312-5
Table 312.6(A).
Table 312.6(A) Minimum Wire-Bending Space Author's Comment: Cable clamps or cable connectors must
Wire Size (AWG or kcmil)
Inches
be used with only one cable, unless that damp or fitting is iden-
8-6
1':
tified for more than one cable. Some Type NM cable clamps are listed for two Type NM cables within a single fitting {UL White Book, Guide Information for Electrical Equipment, www.ul.com/
2
2
21,
1
regulators/2008_Wh iteBook.pdf). Ex: Cables with nonmetallic sheaths aren't required to be secured to the enclosure if the cables enter the top ofa surface-mounted
4-3
1/0-2/0
3! 2
3/0-4/0
4
enclo-
250
sure through a nonflexible raceway not less than 18 in. or more than
300-350
5
10 ft long, if all of the following conditions are met: Figure 312-6
400-500
6
600-700
8
(a) Each cable is fastened within 1 ft from the raceway. (b) The raceway doesn 't penétrate a structural ceiling. (c) Fittings are provided on the raceway to protect the cables from abrasión.
312.8 Enclosures With Spiices, Taps, and FeedThrough Conductors. Cabinets, cutout boxes, and meter socket endosures can be used for conductors as feeding through, spiiced, or tapping off to other enclosures, switches, or overcurrent devices
(d) The raceway is sealed.
where all of the following conditions are met: (e) Each cable sheath extends not less than J4 in. into the (D The total área of the conductors at any cross section doesn't
panelboard.
exceed 40 percent of the cross-sectional área of the space. (f)
The raceway ís properiy
secured.
Figure 312-7
(g) Conductor fill is limited to Chapter 9, Table 1 percentages.
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Mike HoiVs iiiustrated Guide to Understanding tiie 2011 Nationai Eiectricai Code, Volume 1
Cabinets, Cutout Boxes, and IVIeter Socket Enclosure
Switch and Overcurrent Device Enclosures Spiices and Taps 312.812).
Switch and Overcurrent Device Enclosures Spiices. Taps. and Feed-Through Conductors 312.8(11 . J d
A n enclosure can be used as a raceway if the conductors don't fill the wiring space to more than 4 0 % .
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"
^
^
^
|f-T H
! Spiices and taps can be installed in a n i enclosure if the spiices or taps don't fill the wiring space to more than 7 5 % .
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Service conductors and other feeder conductors are permitted in the s a m e enclosure [230.7].
Figure 312-8
Figure 312-7 Switch and Overcurrent Device Enclosures Spiices. Taps. and Feed-Through Conductors
gj The total área of conductors, spiices, and taps installed at any
3ir8m
cross section doesn't exceed 75 percent of the cross-sectional
A warning label o n t h e enclosure identifies t h e closest disconnect for feed-through conductors.
área of that space. Figure 312-8 (3) A warning label on the enclosure identifies the disconnecting means for feed-through conductors. Figure 312-9
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Service conductors and other feeder conductors are permitted in t h e s a m e enclosure [230.7]. Figure 312-9
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ARTICLE
314
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
INTRODUCTION TO ARHCLE 314—OUTLET, DEVICE, PULL AND JUNCTION BOXES; CONDUIT BODIES; AND HANDHOLE ENCLOSURES Article 314 contains instaliation requirements for outlet boxes, pulí and junction boxes, conduit bodies, and handhole enclosures. As with Article 312, the conditions of use have a bearing on the type of material and equipment selected for a particular instaliation. If a raceway is installed in a wet location, for example, the corred fittings and the proper instaliation methods must be used. Article 314 provides guidance for selecting and installing outlet and device boxes, pulí and junction boxes, conduit bodies, and handhole enclosures. Information in this article will help you size an outlet box using the proper cubic-inch capacity as well as calculating the minimum dimensions for larger pulí boxes. There are limits on the amount of weight that can be supported by an outlet box and rules on how to support a device or outlet box to various surfaces. This article will help you understand these type of rules so that your instaliation will be compliant with the NEC. As always, the clear illustrations in this unit will help you visualize the finished instaliation.
PART I. SCOPE AND GENERAL 314.1 Scope.
314.3 Nonmetallic Boxes.
Nonmetallic boxes can only be
used with nonmetallic cables and raceways. Article 314 contains the instaliation requirements
for outlet boxes, conduit bodies, pulí and junction boxes, and hand-
Ex 1: Metal raceways and metal cables can be used with nonmetal-
hole enclosures. Figure 314-1
lic boxes ifall raceways are bonded together in the nonmetallic box
314.4 Metal Boxes. Outlet Boxes, Conduit Bodies, Pull/Junction Boxes. a n d Handhole Enclosures
Metal boxes containing circuits that opér-
ate at SOV or more must be connected to an equipment grounding conductor of a type listed in 250.118 [250.112(1) and 250.148]. Figure 3 1 4 - 2
PART II. INSTALLATION 314.15 Damp or Wet Locations.
Boxes and conduit bodies
in damp or wet locations must prevent moisture or water from entering or accumulating within the enclosure. Boxes, conduit bodies, and fittings installed in wet locations must be listed for use in wet locations. Figure 314-3 Article 314 contains t h e instaliation requirements for outlet boxes, conduit bodies, pulí and junction boxes, a n d handhole enclosures.
Author's Comment: If handhole enclosures without bottoms are installed, all enclosed conductors and any spiices or terminations must be listed as suitable for wet locations [314.30(0)].
Figure 314-1
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Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
Metal B o x e s 314.4
314.16
(A) Box Volume Calculations. The volume of a box includes the total volume of its assembled parts, inciuding plaster rings, extensión rings, and domed covers that are either marked with their volume in cubic inches (cu in.), or are made from boxes listed in Table 314.16(A). Figure 3 1 4 - 4
Metal boxes containing circuits that opérate at 5 0 V or more must be connected t o a n e q u i p m e n t grounding conductor.
Box V o l u m e Calculations 314.16(A) O o
Copyrigni 2011, www MikeHoB com
o o oQo °
O'
Q
4x1V2in. Box w i t h S q u a r e Box Plaster Ring
Box with Extensión Ring -1
Box with Raised Cover
Figure 314-2 Z.
3
Boxes and Conduit Bodies in D a m p or W e t Locations 314.15
21 in.^
2 4 . 3 in.'
4 2 in.3
w
5
2 8 . 5 in.3
T h e v o l u m e of a box includes t h e v o l u m e of its a s s e m b l e d parts that a r e m a r k e d with their c u i n . or are m a d e f r o m b o x e s listed in Table 3 1 4 . 1 6 ( A ) . Copyngfil 2011. www lAkBMoK com
Figure 3 1 4 - 4
(B) Box Fill Calculations. The calculated conductor volume deterBoxes and fittings installed in wet locations must b e listed for use In w e t locations. I VIOLATION Set S c r e w Fitting [358.42]
mined by (1) through (5) and Table 314.16(6} are added together to determine the total volume of the conductors, devices, and fittings. Raceway and cable fittings, inciuding locknuts and bushings, aren't counted for box fill calculations. Figure 314-5
Box Fill Calculations 314.16(B)
Figure 314^3
S m a l l fittings, like cable connectors a n d r a c e w a y fittings (locknuts a n d • bushings), aren't c o u n t e d for box fill calculations. i
314.16 Number of 6 AWG and Smaller Conductors in Boxes and Conduit Bodies. Boxes containing 6 AWG and s-^aller conductors must be sized to provide sufficient free space for
/
aii conductors, devices, and fittings. In no case can the volume of the Sox, as calculated in 314.16(A), be less than the volume requirement
C
as calculated in 314.16(B). Conduit bodies must be sized in accordance with 314.16(C). Author's Comment: The requirements for sizing boxes and
11
conduit bodies containing conductors 4 AWG and larger are contained in 314.28. The requirements for sizing handhole enclosures are contained in 314.30(A).
Figure 314-5
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325
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
314.16
Tabte 314.16(B) Volume Allowance Required per Conductor Conductor AWG
Volume cu in.
18
1.50
16
1.75
14
2.00
12
2.25
10
2.50
8
3.00
6
5.00
Box Fill Calculations - Conductor V o l u m e 314.16(B)(1} 2 - 3 . ^
4-5 6-7i
Device for connecting to unbroken conductor loops with stripped insulation.
Each loop or coil of unbroken conductor that's 12 in. or longer is c o u n t e d a s t w o conductors. E a c h conductor loop less than 12 in. long is counted a s o n e .
Copyiighl 2011,
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(1) Conductor Volume. Each unbroken conductor that runs through a box, and each conductor that terminates in a box, is counted as a
Figure 314-7
single conductor volume in accordance with Table 314.16{B). Figure 314-6
Ex: Equipment grounding conductors,
and up to four 16 AWG ano
smaller fixture wires, can be omitted from box fill calculations if ttiey Box Fill Calculations - Conductor Fill 314.16(B)(1) Eacti c o n d u c t o r of a spiice is c o u n t e d a s o n e .
enter the box from a domed luminaire or similar canopy, such as a ceiling paddie fan canopy. Figure 314-€
Box Fill Calculations - Fixture W i r e s 314.16(B)(1) Ex
Each terminating conductor is c o u n t e d a s o n e . Domed Luminaire or For this e x a m p l e , there are a total of six conductors. Copyrigm 2011, *ww.MikeHo«.com
Figure 314-6
Not m o r e t h a n four fixture wires 16 A W G and smaller can be omitted f r o m box fill calculations, if they enter from a d o m e d luminaire or canopy.
Each loop or coil of unbroken conductor having a length of at Ieast twice the minimum length required for free conductors in 300.14
Figure 314-8
must be counted as hwo conductor volumes. Conductors that origínate and terminate within the box, such as pigtails, aren't counted at all. Figure 314-7
(2) Cable Clamp Volume. One or more internal cable clamps count as a single conductor volume in accordance with Table 314.16(B},
Author's Comment: According to 300.14, at Ieast 6 in. of free conductor, measured from the point in the box where the conductors enter the enclosure, must be left at each outlet, junction,
based on the largest conductor that enters the box. Cable connectors that have their clamping mechanism outside of the box aren't counted. Figure 314-9
and switch point for spiices or terminations of luminaires or devices.
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Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
Box Fill Calculations - C l a m p s 314,16(B)(2)
314.16
Box Fill Calculations - Device Yoke Fill 314.16(B)(4)
Cable or R a c e w a y CONNECTORS O Conductors Internal Cable CLAMPS 1 Conductor
One or more internal cable clamps count as one conductor, based o n t h e largest conductor entering the box. External cable connectors don't count for box fill calculations.
T h e s e devices all have single g a n g yokes. E a c h device yoke counts as t w o conductors based o n t h e largest conductor terminating on t h e device.
Copyrigtil 2011, viww.MikeHoK.com
CopyiigM 2011. « w * MikeHoK com
Figure 314-9
Figure 314-11
(3) Support Fitting Volume. Each luminaire stud or luminaire hickey
Each multigang-device yoke counts as two conductor volumes for
counts as a single conductor volume in accordance with Table
each gang, based on the largest conductor that terminates on the
314.16(B), based on the largest conductor that enters the box. Figure
device in accordance with Table 314.16(B). Figure 314-12
314-10
Box Fill Calculations - Supporting Fittings 314.16(B)(3}
Box Fill Calculations - Device Yoke V o l u m e 314.16(B)(4) T h e yoke won't fit in a o n e g a n g device box.
Luminaire Stud 1 Conductor Each luminaire stud or hickey counts as 1 conductor, based on the largest conductor in the box.
Luminaire Hickey 1 Conductor
Yoke is 4 C o n d u c t o r s ; Total of S e v e n C o n d u c t o r s in This B o x 3/8 in. Mounting S t e m (not c o u n t e d )
Yoke is 4 Conductors;' Total of Eight Conductors in This Box
Each multigang device yoke counts a s two conductor v o l u m e s for e a c h g a n g based on t h e largest conductor that terminates o n t h e device.
CopvTignt 2011. www.MikeHol1.com
Figure 314-10
Figure 314-12
Author's Comment: Luminaire stems don't need to be counted
Author's Comment: A device that's too wide for mounting in
as a conductor volume.
a single-gang box, as described in Table 314.16(A), is counted based on the number of gangs required for the device.
(4) Device Yoke Volume. Each single-gang device yoke (regardless of the ampere rating of the device) counts as two conductor volumes, based on the largest conductor that terminates on the device in accordance with Table 314.16(B). Figure 314-11
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314.16
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
(5) Equipment Grounding
Conductor Volume. All equipment
grounding conductors in a box count as a single conductor volume in accordance with Table 314.16(B), based on the largest equipment grounding conductor that enters the box. Insulated equipment grounding conductors for receptacles having insulated grounding ter-
Question: How many 14 AWG conductors can be pulled through a 4 in. square x 214 in. deep box with a plaster ring with a marking of 3.60 cu in.? The box contains two receptacles, five 12 AWG conductors, and two 12 AWG equipment grounding concíucíors. Figure 314-14
mináis (isolated ground receptacles) [250.146(0)], count as a single conductor volume in accordance with Table 314.16(B). Figure 314-13
(a)3
(c}7
(b)5
(d}9
Answer: (b) 5 Step 1: Determine the volume of the box assembiy [314.16(A)¡: Box Fill Calculations Bonding Conductor Fill 314.16(B)(5)
Box 30.30 cu in. + 3.60 cu in. plaster ring = 33.90 cu in. A4x4x
21/8 in. box will have a gross volume of 34 cu
in., but the Interior volume is 30.30 cu in., as listed in Table 314.16(A).
O n e or more e q u i p m e n t grounding conductors count a s one conductor.
Step 2: Determine the volume of the devices and conductors in the box: Two—receptacles
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A n isolated equipment grounding conductor counts a s a n additional conductor.
4—12 AWG
Five—12AWG
5—12AWG
Two—12 AWG Grounds
1—12 AWG
Total 10—12AWG x 2.25 cu in. = 22.50 cu in. Step 3: Determine the remaining volume permitted for the 14 AWG conductors:
Figure 314-13
33.90 cu in. - 22.50 cu in. = 11.40 cu in. Step 4: Determine the number ofUAWG
conductors permitted
in the remaining volume:
Author's Comment: Conductor insulation isn't a factor that's
14 AWG = 2.00 cu in. each [Table 314.16(B)]
considered when determining box volume calculations.
11.40 cu in./2.00 cu in. = 5 conductors
(C) Conduit Bodies.
Box Fill Calculations Example 314.16(B)
(2) Spiices. Spiices are permitted in conduit bodies that are legibly marked by the manufacturar with their volume and the máximum
Existing C o n d u c t o r and Device V o l u m e : Ten 12 A W G
H o w m a n y 14 A W G conductors can be a d d e d ?
number of conductors permitted in a conduit body is limited in accordance with 314.16(B).
Question: How many 12 AWG conductors can be spiiced
ina15
cu in. conduit body? Figure 314-15 CopyrtgW 2011.
Step Step Step Step
1. Volume of box/ring: 30.3 + 3.6 c u in. = 33.9 c u i n . 2. Volume of existing conductors/devices = 22.5 c u i n . 3. Space remaining: 33.9 - 22.5 = 11.4 c u in. 4 . Number of 14 A W G a d d e d : 11.4/2.0 c u in. = 5
Figure 314-14
328
W¥íw M*>Ho«.com
(^4
(b)6
(0 8
10
Answer: (b) 6 conductors (15 cu in./2.25 cu in.) 12AWG = 2.25 cu in. [Table 314.16(B)[ 15cuin./2.25cuin.
=6
Mike HoiVs Iilustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
314.17
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
Conduit Body - Conductor Spiices 314.16(C)(2)
Author's Comment Unused cable or raceway openings in electrical equipment must be effectively closed by fittings that provide protection substantially equivalent to the wall of the equipment [110.12(A)]. Figure 314-17
U n u s e d R a c e w a y and Cable Openings 3Í4.17(A)
Spiices are only permitted In conduit bodies that are legibly m a r k e d , by the manufacturen with their v o l u m e .
Cable o r Raceway Knockout Filler y * " —
Six 12 A W G Conductors (15 c u in./2.25 c u in.) Plug Filler CopyTig(it2011 www.Mit>eHol1.<
Figure 314-15 Copyri^2(M1
(3) Short-Radius Conduit Bodies. Capped elbows, handy ells, and sen^ice-entrance elbows aren't permitted to contain any spiices. Figure 314-16
W e e p (drain) holes, ventilation openings, a n d other legitímate openings are permitted.
U n u s e d cable or r a c e w a y o p e n i n g s must be closed with fittings that provide equivalent protection [110.12(A)]. Figure 314-17
Short Radius Conduit Bodies 314.16(C)(3) S o m e t i m e s Called: • Jake Elbow • Short Elbow • Pulling Elbow • Córner Elbow
(B) Metal Boxes and Conduit Bodies. Raceways and cables must be mechanically fastened to metal boxes or conduit bodies by fittings designed for the wiring method. See 300.12 and 300.15. (C) Nonmetallic Boxes and Conduit Bodies. Raceways and cables must be secureiy fastened to nonmetallic boxes or conduit bodies by fittings designed for the wiring method [300.12 and 300.15]. Figure
Short-radius conduit bodies must not contain spiices or taps.
314-18
Conductors That Enter Nonmetallic B o x e s a n d Conduit Bodies 314.17 (C)
Spiices can be m a d e in s o m e conduit bodies [314.16(C)(2)]. Copyriom 2 0 n , w w * MiwHon com
Figure 314-16
314.17 Conductors That Enter Boxes or Conduit Bodies. (A) Openings to Be Closed. Openings through which cables or raceways enter must be adequately closed.
R a c e w a y s a n d cables must be secureiy fastened to nonmetallic boxes or conduit bodies by fittings d e s i g n e d for the wiring m e t h o d . Figure 314-18
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314.20
The sheath of type
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
Boxes R e c e s s e d in Walls or Ceilings 314.20
cable must extend not less than Va in. into the
nonmetallic box.
Noncombustible Finished Surface
Author's Comment: Two Type NM cables can terminate in a single cable clamp, if the clamp is listed for this purpose. £x; Type A/M cable terminating to a single-gang (2 Va x 4 in.) device box isn 't required to be secured to the box if the cable is secureiy fas-
M á x i m u m of V4 in. From the Finished Surface
tened within 8 in. ofthe box Figure 314-19
CopyngW 2011. www
Nonmetallic Single G a n g Box - N M Cable 314.17(0) Ex
B o x e s , plaster rings, extensión rings, or listed extenders must have the front edge set back no more than V4 in. from t h e noncombustible finished surface. Figure 314-20
Metal Studs B o x e s R e c e s s e d in Walls or Ceilings 374.20 Combustible Finished Surface N M cable terminating to a single-gang {2V4 in. x 4 in.) device box isn't required to be secured to the box if the cable is secureiy fastened within 8 in. of the box. Flush With or Project Out From the Surface
Figure 314-19
314.20 Boxes Recessed in Walls or Ceilings.
Boxes
having flush-type covers that are recessed in walls or ceilings of noncombustible material must have the front edge of the box, plaster ring, extensión ring, or listed extender set back no more than Va in. from the finished surface. Figure 314-20 In walls or ceilings that are constructed of wood or other combustible material, boxes must be installed so the front edge of the enclosure, plaster ring, extensión ring, or listed extender is flush with, or projects
B o x e s , plaster rings, extensión rings, or listed extenders must have the front e d g e flush with, or project out from, the combustible finished surface. Figure 314-21
314.22 Surface Extensíons.
Surface extensions can only
be made from an extensión ring mounted over a flush-mounted box. Figure 314-23
out from, the finished surface. Figure 314-21 Ex: A surface
extensión can be made from the cover of a flush-
Author's Comment: Plaster rings and extensión rings are avail-
mounted box if the cover is designed so it's unlikely to fall off if the
able in a vahety of depths to meet the above requirements.
mounting screws become loóse. The surface extensión wiring method must be flexible to permit the removal of the cover and provide
314.21 Repairing Noncombustible Surfaces,
Gaps
around boxes with flush-type covers that are recessed in noncombustible surfaces (such as plaster, drywail, or plasterboard) must be
access
to the box interior, and equipment grounding continuity must
be independent of the connection between the box and the cover. Figure 314-24
repaired so there will be no gap more than V& in. at the edge of the box. Figure 314-22
330
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Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
314.23
Surface Extensión from a Cover 314.22 Ex
Repairing Noncombustible Surfaces A r o u n d Boxes 314.21
Extensión f r o m a cover Is permitted if: • T h e cover is d e s i g n e d not to fall off. • A f l e x i b l e w i h n g m e t h o d is u s e d . • T h e g r o u n d i n g connection is independent from the cover.
Violation Gap Over 1/8th in. Máximum 1/8th in. Gap
Surface Extensión From a Cover
Gaps around boxes with flush-type covers that are recessed in noncombustible surfaces must be repaired so there will be no g a p greater than 1/8th in. at the edge of the box. CopyngN 2011.
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Figure 314-22
Figure 314-24
(2) Braces. Metal braces no less than 0.02 in. thick and wood bracos Surface Extensions 314.22
not less than a nominal 1 in. x 2 in. can support a box.
ao.c
(C) Finished Surface Support. Boxes can be secured to a finished surface {drywail or plaster walls or ceilings) by clamps, anchors, or fittings identified for the purpose. Figure 314-25
Extensión Ring
Surface Extensión Box Support - Finished Surface 314.23(0}
Surface extensions f r o m a box must be m a d e f r o m an extensión ring that's installed over the box.
Copyright 2011.
, ! Fished Cable
Cut-in B o x
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Figure 314-23
314.23 Support of Boxes and Conduit Bodies.
Boxes
must be secureiy supported by one of the following methods:
Bracket Provides Support for Box
(A) Surface. Boxes can be fastened to any surface that provides ade-
B o x e s can be s e c u r e d t o a finished surface by c l a m p s , anchors, or fittings identified for the purpose.
quate support. (B) structural Mounting. Boxes can be supported from a structural
com^7a^^.
Figure 314-25
member of a building or supported from grade by a metal, plástic, or wood brace. (1) Nails and Screws. Nails or screws can be used to fasten boxes, provided the exposed threads of screws are protected to prevent abrasión of conductor insulation.
(D) Suspended-Ceiling Support. Outlet boxes can be supported to the structural or supporting elements of a suspended ceiling, if secureiy fastened by one of the following methods;
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314.23
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
(1) Celling-Framing Members. An outlet box can be secured to sus-
Box Support - I n d e p e n d e n t Support W i r e s 314.23(D)(2)
pended-ceiling framing members by boits, screws, rivets, clips, or other means identified for the suspended-ceiling framing member(s).
Independent support wires can be used to secure electrical wiring [300.11 (A)].
Figure 314-26
Box Support - Ceiling Framing M e m b e r s 314.23(D)(1)
Outlet boxes can be s e c u r e d , with fittings identified for I the p u r p o s e , to ceiling a n d independent support wires " that are taut a n d secured at both ends.
Outlet boxes can be secured l o suspended-ceiling m e m b e r s by bolts, screws, rivets, clips, or other m e a n s identified for the purpose.
Figure 314-27
Box Support - T h r e a d e d Raceways No Devices or Luminaires 314.23(E) Enclosure Not Over 1 0 0 cu i n .
Figure 314-26
36 in. Author's Comment: If framing members of suspended-ceiling systems are used to support luminaires, they must be secureiy fastened to each other and must be secureiy attached to the building structure at appropriate intervals. In addition, luminaires must be attached to the suspended-ceiling framing members
36 in.
T w o t h r e a d e d IMC o r R M C can support an outlet box without devices or luminaires, if e a c h raceway is supported within 3 6 in., or within 18 in. if all conduits are o n one side.
with screws, bolts, rivets, or clips listed and identified for such use [410,36(B)]. Cop/right 2011. www
(2) Independent Support Wires. Outlet boxes can be secured, with fittings identified for the purpose, to the ceiling-support wires. If inde-
Figure 314-28
pendent support wires are used for outlet box support, they must be taut and secured at both ends [300.11 (A)]. Figure 314-27 Author's Comment: See 300.11 (A) on the use of independent support wires to support raceways and cables. (E) Raceway—Boxes and Conduit Bodies Vl/ithout Devices or Luminaires. Two intermedíate metal or rigid metal conduits, threaded wrenchtight into the enclosure, can be used to support an outlet box
(1) Intermedíate metal conduit, Type IMC (2) Rigid metal conduit, Type RMC (3) Rigid polyvinyl chioride conduit, Type PVC (4) Reinforced thermosetting resin conduit, Type RTRC (5) Electrical metallic tubing, Type EMT
that doesn't contain a device or luminaire, if each raceway is sup-
(F) Raceway—Boxes and
Conduit
Bodies with Devices or
ported within 36 in. of the box or within 18 in. of the box if all conduit
Luminaires. Two intermedíate metal or rigid metal conduits, threaded
enfries are on the same side. Figure 314-28
wrenchtight into the enclosure, can be used to support an outlet box containing devices or luminaires, if each raceway is supported within
Ex: Conduit bodies are permitted to be supported by any of the follow-
18 in. of the box. Figure 314-29
ing wiring methods:
Mike HoiVs iliustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
Covers a n d Canopies 314.25
Box Support - T h r e a d e d R a c e w a y s With Devices and Luminaires 314.23(F)
I
I
[, Two threaded IMC or R M C c a n support an outlet box with devices or luminaires if e a c h r a c e w a y is supported within 18 i n . VIOLATION T h e conduit must be t h r e a d e d and directly connected t o the box.
314.23
Blank cover plates c a n cover a n outlet box.
A faceplate or luminaire can cover a n outlet box. W h e n a n instaliation is complete, e a c h outlet box must be provided with a cover, faceplate, luminaire canopy, lampholder, o r similar device. CopyrtQMl 2011.
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Figure 314-29
Figure 314-31
(H) Pendant Boxes.
(A) Nonmetallic or Metallic. Nonmetallic covers are permitted on
(I) Flexible Cord. Boxes containing a hub can be supported from a cord connected to fittings that prevent tensión from being transmitted to joints or termináis [400.10]. Figure 314-30
any box, but metal covers are only permitted if they can be connected to an equipment grounding conductor of a type recognized in 250.118, in accordance with 250.110 [250.4(A)(3)]. Figure 314^32
Box Support - Pendant Cord 314.23(H)(1)
É p Boxes can be supported from a cord that's connected to fittings s o that tensión isn't transmitted to joints or termináis.
K | tí
i
Nonmetallic covers or plates are permitted o n a n y box, but metallic faceplates, w h e r e u s e d , must be connected t o a n e q u i p m e n t grounding conductor. CopyrigM 2011.
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CocyngN 2011, www MikaHolt.com
Figure 314-32 Figure 314-30 Author's Comment: Metal switch faceplates [404.9(B)] and Author's Comment: Only cords identified for use as pendants in Table 400.4 may be used for pendants.314.25 Covers and
metal receptacle faceplates [406.6{A)] must be connected to an equipment grounding conductor
Canopies. When the instaliation is complete, each outlet box must be provided with a cover or faceplate, unless covered by a fixture canopy, lampholder, or similar device. Figure 314-31
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314.27
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
314.27 Outlet Box.
(2) Luminaire Outlets in the Ceiling. Boxes for a luminaire in a ceiling must be designed to support a luminaire weighing a minimum of
(A) Boxes at Luminaire Outlets.
50 Ib. Luminaires weighing more than 50 Ib must be supported indef1) Luminaire Outlets in the Wall. Boxes for a luminaire in a wall
pendently of the outlet box unless the outlet box is listed and marked
must be designed for the purpose and marked on the interior of the
for the máximum weight to be supported. Figure 314-35
box to indícate the máximum weight of the luminaire if other than 50 Ib. Figure 314-33 Luminaire and Lampholder Outlets in Ceiling 314.27(Am Luminare and Lampholders - Outlets in t h e Wall
Boxes and fittings for luminaires a n d lampholders in a wall must be marked o n t h e interior of the box to indícate the m á x i m u m weight of the luminaire if other than 5 0 Ib.
Lighting outlet boxes in a ceiling must be designed to support a luminaire weighing at Ieast 50 Ib.
Luminaires over 50 Ib must be supported independently of the lighting outlet box unless the outlet box is listed and marked for the máximum weight of the luminaire.
Figure 314-35
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Figure 314-33 (B) Floor Box. Floor boxes must be specifically listed for the purpose. Figure 314-36 Ex: A wall-mounted luminaire weighing no more than 6 Ib can be supported to a device box or plaster ring secured to a device box. Figure 314-34
Floor Outlet B o x 314.27(8}
Luminare and Lampholder Outlets in the Wall 314.27(A){1_) Ex
I
Device Box or Plaster Ring
A wall-mounted luminaire or lampholder weighing no m o r e than 6 Ib can be supported to a device box or plaster ring.
I
i
Floor outlet boxes must be listed for the purpose.
Figure 314-36
Figure 314-34
334
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
(C) Ceiling Paddie Fan Box. Outlet boxes for a ceiling paddie fan must be listed and marked as suitable for the purpose, and must not
314.28
Outlet B o x e s for Utilization Equipment 314.27(0) Ex
support a fan weighing more than 70 Ib. Outlet boxes for a ceiling paddie fan that weighs more than 35 Ib must include the máximum weight to be supported in the required marking. Figure 314-37
Outlet Box - Ceiling Paddie Fan 314.27(0}
Utilization e q u i p m e n t 6 Ib or less can b e supported by any box or plaster ring secured t o a b o x if supported by at Ieast t w o No. 6 or larger screws. Copyr>ght2011 www. MikeHolt com
Figure 314-38 Fan outlet boxes must be listed, marked as suitable for the purpose, and can't support a fan that weighs more than 70 Ib.
314.28 Boxes and Conduit Bodies for Conductors 4 AWG and Larger. Boxes and conduit bodies containing conduc-
Paddie fans over 70 Ib must b e supported independently of the box.
tors 4 AWG and larger that are required to be insulated must be sized so the conductor insulation won't be damaged. Figure 314-39
Figure 314-37
Author's Comment: If the máximum weight isn't marked on the box, and the fan weighs over 35 Ib, the fan must be sup-
Pulí and Junction B o x e s - 4 A W G a n d Larger 314.28 Straight Pulís
ported independently of the outlet box, Ceiling paddie fans over 70 Ib must be supported independently of the outlet box. 1
-I
Í
Sections 3 1 4 . 2 8 ( A ) t o (D) are used to size pulí boxes, junction boxes, and conduit bodies w h e n conductor sizes 4 A W G and larger are used.
¡
Where spare, separately switched, ungrounded conductors are proA n g l e Pulís
vided to a ceiling-mounted outlet box, in a location acceptable for a ceiling-suspended (paddie) fan in single or multifamily dweilings, the outlet box or outlet box system must be listed for the support of a ceiling-suspended (paddie) fan. (D) Utilization Equipment. Boxes used for the support of utilization equipment must be designed to support equipment that weighs a minimum of 50 Ib [314.27(A)]. Figure 314-39 Ex: Utilization equipment weighing 6 Ib or less is permitted to be supported by any box or plaster ring secured to a box, provided the equipment is secured with no fewer than two No. 6 or larger
screws.
Figure 314-38
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U Pulís
314.28
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
Ex: When conductors enter an enclosure with a removable cover, the distance from where the conductors
enter to the removable
cover
Pulí Box, Junction Box, a n d Conduit Body Covers 314.28(C)
must not be less than the bending distance as listed in Table 312.6(A) for one conductor per terminal. Figure 314-47
Pulí Box and Conduit Body Sizing - Depth 314.28(A)(2) Ex Dimensión D 500 kcmil = 6 i n .
•D
T h e metal r a c e w a y and enclosure is t h e equipment i g r o u n d i n g conductor to w h i c h the covers connect. • Metal c o v e r s f o r pulí b o x e s , junction b o x e s , and conduit bodies must be connected t o a n e q u i p m e n t grounding conductor in a c c o r d a n c e with 250.110. Figure 314-48
The distance from vi^here t h e conductors enter to the removable cover can't be less than the bending distance listed in Table 312.6(A) for one wire per terminal. Figure 314-47
Power Distribution Biocks ín Pull/Junction Boxes 314.28(E) Power Distribution Block
(3) Smaller Dimensions. Boxes or conduit bodies smaller than those required in 314.28(A)(1) and 314.28(A)(2) are permitted, if the enclosure is permanently marked with the máximum number and máximum size of conductors. (B) Conductors in Pulí or Junction Boxes. Pulí boxes or junction boxes with any dimensión over 6 ft must have all conductors cabled or racked in an approved manner. (C) Covers. Pulí boxes, junction boxes, and conduit bodies must have a cover suitable for the conditions. Nonmetallic covers are permitted
Copynghl Z011. « w * P*keHolt ojm
Power distribution biocks in pulí and junction boxes must: (1) Be listed as a power distribution block. (2) Be installed in a box with dimensions not smaller than specifiedin.íhe instaliation instructjons.of the block, f3) Comply with 312.6 for wire-bending space at termináis (4) Have no uninsulated exposed live parts. wtiether the junction/pull box cover is on or off. Figure 314-49
on any box, but metal covers are only permitted if they can be connected to an equipment grounding conductor of a type recognized in
(3) Wire-Bending Space. The junction box is sized so that the wire-
250.118, in accordance with 250.110 [250.4(A)(3)]. Figure 314-48
bending space requirements of 312.6 can be met.
(E) Power Distribution Block. Power distribution biocks installed in
(4) Live Parts. Exposed live parts on the power distribution block
junction boxes over 100 cu in. must comply with the following: Figure
aren't present when the junction box cover is removed.
314-49
(5) Through Conductors. Where the junction box has conductors that
(1) Instaliation. Be listed as a power distribution block.
don't terminate on the power distribution block(s), the through con-
(2) Size. Be installed in a box not smaller than required by the instal-
ductors must be arranged so the power distribution block termináis are unobstructed following instaliation.
iation instructions ofthe power distribution block.
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
314.29 Wiring to be Accessible. Boxes, conduit bodies, and
314.30
Handhole Enclosure 314.30
tiandhole enclosures must be installed so that the wiring is accessible without removing any part of the building, sidewaiks, paving, or earth.
H a n d h o l e enclosures must be identified for u n d e r g r o u n d use, a n d be designed a n d installed to withstand all loads likely to be i m p o s e d .
Figure 314-50
Wiring in Boxes, Conduit Bodies, a n d H a n d h o l e s Must be Accessible 314.29
d
Accessible by \ Removing Ceiling Panels p ¡ ^ Copyright 20i 1. -ww. WkeHoW.com
Boxes, conduit bodies, a n d handfiole enclosures must be installed so that t h e wiring contained in t h e m can be m a d e accessible without removing a n y part of the building, or excavating sidewaiks, paving, or the earth. Accessible by Removing Device
Accessible by R e m o v i n g Floor Panels
Figure 314-51
Handhole Enclosure Mechanical R a c e w a y a n d Cable Connection 314.30(B) Underground raceways a n d cables entering a handhole enclosure aren't required to be mechanically connected to the handhole enclosure.
Figure 314-50
Ex: Listed boxes and handhole enclosures can be buried if covered by gravel, light aggregate, or noncohesive granulated soil, and their loca-
Spiices or terminations must be listed a s suitable for w e t locations [314.30(C)].
tion is effectively identified and accessible for excavation.
314.30 Handhole Enclosures.
Handhole enclosures must be
Figure 314-52
identified for underground use, and be designed and installed to withstand all loads likely to be imposed on them. Figure 314-51 (A) Size. Handhole enclosures must be sized in accordance with
(C) Enclosure Wiring. Spiices or terminations within a handhole must be listed as suitable for wet locations [110.14(B)].
314.28{A). For handhole enclosures without bottoms, the measurement to the removable cover is taken from the end of the raceway or
(D) Covers. Handhole enclosure covers must have an identifying
cable assembiy. When the measurement is taken from the end of the
mark or logo that prominently identifies the function of the enclosure,
raceway or cable assembiy, the valúes in Table 312.6(A) for one wire
such as "electric." Handhole enclosure covers must require the use of
to terminal can be used [314.28(A)(2) Ex].
tools to open, or they must weigh over 100 Ib.
(B) Mechanical Raceway and Cable Connection. Underground raceways and cables entering a handhole enclosure aren't required to be mechanically connected to the handhole enclosure. Figure 314-52
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314.30
Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; and Handhole Enclosures
Metal covers and other exposed conductive surfaces of handhole enclosures must be connected to an equipment grounding conductor sized to the overcurrent device in accordance with 250.122 [250.102(0)]. Metal covers of handhole enclosures containing service conductors must be connected to an equipment bonding jumper sized in accordance with Table 250.66 [250.92 and 250.102(0)]. Figure
H a n d h o l e Enclosure Bonding Covers a n d E x p o s e d Conductive Surfaces 314,30(D) Metal covers and other exposed conductive surfaces of handhole enclosures must be connected to an EGC sized to the overcurrent device using 250.122. If enclosing service conductors the E G C is sized using Table 250.66.
314-53
Figure 314-53
340
Mike Hoit's Iliustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
ARTICLE
320
Armored Cable (Type AC)
INTRODUCTION TO ARTICLE 320—ARMORED CABLE (TYPE AC) Armored cable is an assembiy of insulated conductors, 14 AWG through 1 AWG, individuaily wrapped within waxed paper and contained within a flexible spiral metal sheath. The outside appearance of armored cable looks like flexible metal conduit as well as metal-ciad cable to the casual observer. This cable has been referred to as "BX®" cable over the years and used in residential wiring in some áreas of the country.
PART I. GENERAL 320.1 Scope.
Author's Comment: The conductors are contained within a flexible metal sheath that intedocks at the edges, with an internal
This article covers the use, instaliation, and con-
struction specifications of armored cable, Type AC.
aluminum bonding strip, giving the cable an outside appearance similar to that of flexible metal conduit. Many electricians cali this metal cable "BX®" The advantages of any flexible cables, as
320.2 Definition.
compared to raceway wiring methods, are that there's no limit to
Armored Cable (Type AC). A fabricated assembiy of conductors in a flexible interlocked metal armor with an internal bonding strip in intí-
the number of bends between terminations and the cable can be quickiy installed.
mate contact with the armor for its entire length. See 320.100. Figure 320-1
PART II. INSTALLATION A r m o r e d Cable - Type A C 320.2 Definition W a x e d Paper Jute
320.10 Uses Permitted.
TypeAC cable ís permitted as follows:
(1) Feeders and branch circuits in both exposed and concealed installations. (2) Cable trays. (3) Dry locations.
Interlocked Spiral Metal Sheath
(4) Embedded in plaster or brick, except in damp or wet locations. Bonding Strip
A fabricated assembiy of conductors in a flexible interiocked metal armor with an internal bonding strip in intímate contact with the armor for its entire length.
(5) Air voids where not exposed to excessive moisture or dampness. Note: The "Uses Permitted" isn't an all-inclusive list, which indicates that other suitable uses are permitted if approved by the authority having jurisdiction.
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Author's Comment: Type AC cable is aiso permitted to be Figure 320-1
installed in a cavity plenum space [300.22(C)(1)].
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320.12 Uses Not Permitted.
Type AC cable must not be
installed in any of the following locations:
Author's Comments: • 300.4{A)(1) Drilling Holes in Wood Members. When holes through wood framing members for cables, the edge of
(1) It subject to physical damage.
the holes must be not less than VA in. from the edge of the (2) In damp or wet locations.
wood member, Figure 320-3A
(3) In air voids of masonry block or tile walls where such walls are
If the edge of the hole is less than I V i in. from the edge, a
exposed or subject to excessive moisture or dampness.
V\b in. thick steel píate of sufficient length and width must be installed to protect the wiring method from screws and nails.
(4) Where exposed to corrosive conditions.
320.15 Exposed Work.
Exposed Type AC cable must closely
follow the surface of the building finish or running boards. Type AC cable installed on the bottom of floor or ceiling joists must be secured at every joist, and must not be subject to physical damage. Figure 320-2
Figure 320-3B • 300.4(A)(2) Notching Wood Members. If notching of wood framing members for cables is permitted by the building code, a '/i6 in. thick steel píate of sufficient length and width must be installed to protect the cables and raceways from screws and nails. Figure 320-3C • 300.4(D) Cables Parallel to Framing Members and Furring Strips. Cables installed parallel to framing members or furring strips must be protected where likely to be penetrated by nails
A C Cable - E x p o s e d Work 320.15
or screws. The wiring method must be installed so it's at Ieast 1 VA in. from the nearest edge of the framing members or furring strips, or a '/e in, thick steel píate must protect the wiring method. Figure 320-4
A C Cable - T h r o u g h W o o d Framing Members 320.17
Bored Hole, [300.4(A)(i: VA in. or More, N o Steel Píate Required
Type A C cable run o n t h e bottom of floor or ceiling joists must be secured at every joist and not subject to physical d a m a g e .
Bored Hole, [300.4(A)(1)] Less T h a n 1 % in. Steel Píate Required ¡ Coo*"gm2Cil
*w*M*eHoncom
Notch (if permitted) | [300.4(A)(2)] Steel Píate Required
Figure 320-2 Figure 320-3
320.17 Through or Parallel to Framing Members. Type AC cable installed through, or parallel to, framing members or furring strips must be protected against physical damage from penetration by screws or nails by maintaining VA in. of separation, or by installing a suitable metal píate in accordance with 300.4(A), (C), and (D).
342
Mike HoiVs Iliustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Armored Cable (Type AC)
320.30
A C Cable - Parallel t o Framing M e m b e r s a n d Furring Strips 320.17 X
T y p e A C Cable '•• Bending Radius 320.24 Framing Member
X
Cable must be at Ieast VA in. from the nearest edge of a framing m e m b e r or furring strip, or be protected by a steel píate or sieeve [300.4(D)].
Framing Member
Inner Edge of Bend
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Radius 2.50 in.
T h e Radius of the C u r v e 5 X 0.50 in. = 2.50 in. T h e radius of the inner edge of the curve must not be less t h a n 5 times the diameter of the cable. Figure 320-5
Figure 320-4
A C Cable - Securing 320.30(B)
320.23 In Accessible Attics or Roof Spaces. (A) Cables Run Across the Top of Floor Joists. Where run across Máximum 4V2ft
the top of floor joists, or across the face of rafters or studding within 7 ft of floor or floor joists, the cable must be protected by substantial guard sthps that are at Ieast as high as the cable. If this space isn't accessible by permanent stairs or ladders, protection is required only within 6 ft of the nearest edge of the scuttie hole or attic entrance.
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(B) Cable Installed Parallel to Framing Members. Where Type AC cable is installed on the side of rafters, studs, ceiling joists, or floor Type AC cable must be secured within 12 in. of termination and every 4 V2 ft.
joists, no protection is required if the cable is installed and supported so the nearest outside surface of the cable or raceway is at Ieast V/A in. from the nearest edge of the framing member [300.4(0)].
320.24 Bends.
Type AC cable must not be bent in a manner that
will damage the cable. This is accomplished by limiting bending of the inner edge of the cable to a radius of not less than five times the
Figure 320-6
Author's Comment: Type AC cable is considered secured when installed horizontally through openings in wooden or metal framing members [320,30(C)].
diameter of the cable. Figure 320-5 (C) Supporting. Type AC cable must be supported at intervals not
320.30 Securing and Supporting.
exceeding AV2 ft. Cables installed horizontally through wooden or
(A) General. Type AC cable must be supported and secured by Sta-
metal framing members are considered supported if support doesn't
ples, cable ties, straps, hangers, or similar fittings, designed and
exceed 4^2 ft. Figure 320-7
installed so as not to damage the cable.
(D) Unsupported Cables. Type AC cable can be unsupported where
(B) Securing. Type AC cable must be secured within 12 in. of every
the cable is:
outlet box, junction box, cabinet, or fitting, and at intervals not exceed-
(1) Fished through concealed spaces in finished buildings or struc-
ing 4V2 ft. Figure 320-6
tures, if support is impracticable; or
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343
320.40
Armored Cable (Type AC)
A C Cable - Horizontal Support 320.30(C)
A C Cable - Fittings 320.40 *
Listed A C Cable Fitting
^ J2
A C cable run horizontally t h r o u g h steel or w o o d framing m e m b e r s is considered supported w h e r e s u c h support doesn't e x c e e d 4V2 ft.
VIOLATION Not Listed f o r A C Cable
A C cable must terminate in b o x e s or fittings specifically listed to protect the conductors f r o m abrasión. Copyrighl 2011, www KíikeMotl com
Figure 320-7
Figure 320-9
(2) Not more than 2 ft long at termináis where flexibility is necessary;
An insulating anti-short bushing, sometimes called a "redhead," must
or
be installed at all Type AC cable terminations. The termination fitting
(3) Not more than 6 ft long from the last point of cable support to the point of connection to a luminaire or other piece of electrical
must permit the visual inspection of the anti-short bushing once the cable has been installed. Figure 320-10
equipment within an accessible ceiling. Type AC cable fittings are permitted as a means of cable support. Figure 320-8 A C Cable - B o x e s a n d Fittings Anti-Short Bushing 320.40
A C Cable - Unsupported in Accessible Ceilings 320.30(D)(3)
X X ^ X . ^
Last Point of Cable Support p ^ ^ >
A n insulating anti-short bushing must ' be installed at cable terminations.
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Unsupported A C cable in lengths not exceeding 6 ft is permitted w h e n installed within an accessible ceiling. Figure 320-8
Figure 320-10
Author's Comments: • The internal aluminum bonding strip within the cable serves
320.40 Boxes and Fittings. Type AC cable
no electrical purpose once outside the cable, and can be cut must termínate in
boxes or fittings specifically listed for Type AC cable to protect the con-
off, but many electricians use it to secure the anti-short bushing to the cable. See 3 2 0 . 1 0 8 .
ductors from abrasión [300.15]. Figure 320-9
344
mke Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Armored Cable (Type AC)
320.108
• Conductors 4 AWG and larger that enter an enclosure must be protected from abrasión during and after instaliation by a fitting that provides a smooth, rounded, insulating surface, such as an insulating bushing unless the design of the box, fitting, or enclosure provides equivalent protection in accordance with 300.4(6).
Author's Comments: • The best method of cutting Type AC cable is to use a tool specially designed for the purpose, such as a rotary armor cutter. • When cutting Type AC cable with a hacksaw, be sure to cut only one spiral of the cable and be careful not to nick the conductors; this is done by cutting the cable at an angle, Breaking the cable spiral (bending the cable very sharply), then cutting
320.80 Conductor Ampacity.
the cable with a pair of dikes isn't a good practice.
(A) Thermai Insulation. Conductor ampacity is calculated on the 90°C insulation rating of the conductors, however the conductors
320.108 Equipment Grounding Conductor.
must be sized to the termination temperature rating in accordance
cable must provide an adequate path for fault current as required by
with 110.14(C)(1). Figure 320-11
250.4(A)(5) or 250.4(B)(4) to act as an equipment grounding conduc-
Type AC
tor. Figure 320-12 T y p e A C Cable Ampacity in Thermai Insulation 320.80(A)
A C Cable - Equipment G r o u n d i n g Conductor 320.108
Conductor ampacity is calculated on the 90°C insulation rating of the conductors, however the conductors must be sized to the termination temperature rating in accordance with 110.14(C)(1).
\
T y p e A C cable provides a n adequate path for fault current t o act a s a n equipment grounding conductor in a c c o r d a n c e with 250.118(8).
T h e bonding strip can be cut off at the termination or it can be u s e d to secure the anti-short bushing.
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Figure 320-11 Figure 320-12
Question: What's the ampacity of four 12 THHN current-carrying conductors installed in TypeAC cable? (a) 18A
(b)24A
Author's Comment: The internal aluminum bonding strip isn't an equipment grounding conductor, but it allows the interlocked
(c) 27A
(d) 30A
armor to serve as an equipment grounding conductor because it reduces the impedance of the armored spirals to ensure that
Answer:
24A
a ground fault will be cleared. It's the combination of the alu-
Table 31015(B)(16) ampacity if 12 THHN is 30A
minum bonding strip and the cable armor that creates the
Conductor Adjusted Ampacity = 30A x 0.80 [Table 31015(B)(3)(a)]
equipment grounding conductor. Once the bonding strip exits the cable, it can be cut off because it no longer serves any purpose.
Conductor Adjusted Ampacity = 24A
The effective ground-fault current path must be maintained by the use of fittings specifically listed for Type AC cable [320.40].
PART III. CONSTRUCTION SPECIFICATIONS 320.100 Construction. Type AC cable
See 300.12, 300.15, and 300.100.
has an armar of flexible
metal tape with an internal aluminum bonding strip in intímate contact with the armor for its entire length.
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ARTICLE
330
Metal-Ciad Cable (Type MC)
INTRODUCTION TO ARTICLE 330—METAL-CLAD CABLE (TYPE MC) Metal-dad cable endoses insulated conductors in a metal sheath of either corrugated or smooth copper or aluminum tubing, or spiral interlocked steel or aluminum. The physical characteristics of Type MC cable make it a versatile wiring method that you can use in almost any location, and for almost any application. The most commonly used Type MC cable is the interlocking kind, which looks similar to armored cable or flexible metal conduit. Traditional interlocked Type MC cable isn't permitted to serve as an equipment grounding conductor, therefore this cable must contain an insulated equipment grounding conductor in accordance with 250.118(1). There is a fairly new produd called interlocked Type MC^ cable containing an aluminum grounding/bonding conductor running just below the metal armor, which allows the sheath to serve as an equipment grounding conductor [250.118(10)(b)].
PART I. GENERAL 330.1 Scope.
Author's Comment: Because the outer sheath of interlocked Type MC cable isn't listed as an equipment grounding conductor,
Article 330 covers the use, instaliation, and con-
it contains an equipment grounding conductor [330.108].
struction specifications of metal-dad cable.
330.2 Definition. Metal-Ciad Cable (Type MC). A factory assembiy of insulated circuit conductors, with or without optical fiber members, enclosed in an armor of interlocking metal tape or a smooth or corrugated metal-
PART II. INSTALLATION 330.10 Uses Permitted. (A) General Uses.
lic sheath. Figure 330-1
(1) In branch circuits, feeders, and services Metal-Ciad Cable (Type M C Cable) 330.2 Definition
(2) In power, lighting, control, and signal circuits (3) Indoors or outdoors (4) Exposed or concealed
Type M C
(5) Directly buried (if identified for the purpose)
Interlocking Metal Sheath (6) In a cable tray (7) In a raceway (8) As aerial cable on a messenger
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A factory assembiy of o n e or more insulated circuit conductors enclosed in a n armor of interlocking metal tape, or a smooth or corrugated metallic sheath.
(9) In hazardous locations as permitted in 501.10(B), 502.10(8), and 503.10 (10) Embedded in plaster or brick
Figure 330-1
346
(11) In wet locations, if any of the following are met:
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
I-Clad Cable (Type MC)
330.17
a. The metallic covering is impervious to moisture. b. A moisture-impervious jacket is provided under the metal
330.17 Through or Parallel to Framing Members. Type MC cable installed through or parallel to framing members or furring strips must be protected against physical damage from pen-
covering.
etration of screws or nails by maintaining a VA in. separation, or by
c. The insulated conductors under the metallic covering are
installing a suitable metal píate in accordance with 300.4(A) and (D).
listed for use in wet locations and a corrosion-resistant jacket is provided over the metallic sheath. (12' If single-conductor cables are used, all circuit conductors must
Author's Comments: • 300.4(A)(1) Drilling Holes in Wood Members. When drilling
be grouped together to minimize induced voltage on the sheath
holes through wood framing members for cables, the edge of
[300.3(B)].
the holes must be not less than VA in. from the edge of the wood member Figure 330-2A
(B) Specific Uses.
If the edge of the hole is less than VA in. from the edge, a
(1) Cable Tray. Type MC cable installed in a cable tray must comply with 392.10, 392.12, 392.10(E). 392.10(L), 392.10(N), 392.30ÍA), 392.46, and 392.56.
VÍ6 in. thick steel píate of sufficient length and width must be installed to protect the wiring method from screws and nails. Figure 330-2B • 300.4(A)(2) Notching Wood Members. If notching of wood
(2) Direct Buried. Direct-buried cables must be protected in accorwith 300.5.
framing members for cables is permitted by the building code, a '/e in. thick steel píate of sufficient length and width must
(3) Installed as Service-Entrance Cable. Type MC cable is permitted for service entráñeos, when installed in accordance with 230.43.
be installed to protect the cables and raceways from screws and nails. Figure 330-2C • 300.4(D) Cables Parallel to Framing Members and Furring
(4) Installed Outside of Buildings or Structures. Type MC cable
Strips. Cables installed parallel to framing members or furring
installed outside oí buildings or structures must comply with 225.10,
strips must be protected where likely to be penetrated by nails
396.10, and 396.12.
or screws. The wiring method must be installed so it's at Ieast 11/4 in. from the nearest edge of the framing member or fur-
Note: The "Uses Permitted" isn't an all-inclusive list, which indicates that other suitable uses are permitted if approved by the authority having jurisdiction.
330.12 Uses Not Permitted.
ring strips, or a '/e in. thick steel píate must protect it. Figure 330-3
Type MC cable must not be used
where:
M C Cable - T h r o u g h Framing
(1) Subject to physical damage. Bored Hole, [300.4(A)(1)] VÁ in. or M o r e , No Steel Píate Required
(2) Exposed to the destructive corrosive conditions in (a) or (b), unless the metallic sheath or armor is resistant or protected by material resistant to the conditions: (a) Direct burial in the earth or embedded in concrete unless identified for the application.
^.r^-*^, I ^
B o r e d Hole. r300.4(A)í1)] Less T h a n 1 Vi i n . Steel Píate Required
(b) Exposed to cinder filis, strong chiorides, caustic alkalis, or vapors of chiorine or of hydrochioric acids.
Notch (if permitted) [300.4(A){2)] Steel Píate Required Copyright 2011. www.MlktHoa com
Figure 330-2
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347
Metal-Ciad Cable (Type MC)
330.23
MC Cable Parallel to Framing M e m b e r s and Furring Strips Protection Against Physical D a m a g e 330.17 -_¿ Framing ; Member,
(A) Smooth-Sheath Cables. (1) Smooth-Sheath Type MC cables must not be bent so the bending radius of the inner edge of the cable is less than 10 times the external diameter of the metallic sheath for cable up to % in. in
i ¡
Cable must be at Ieast VA in. from t h e nearest edge of a framing m e m b e r or furring strip, or be protected by a steel píate or sieeve [300.4(D)].
external diameter. (B) Interlocked or Corrugated Sheath. Interiocked- or corrugatedsheath Type MC cable must not be bent so the bending radius of the inner edge of the cable is less than seven times the external diameter of the cable. Figure 330-4
Framing Member Interiocked or Corrugated-Sheath Type M C Cable Bending Radius 330.24(B) Inner E d g e of Bend Figure 330-3
330.23 In Accessible Attics or Roof Spaces.
0.50 in. O.D. lype MC
cable installed in accessible attics or roof spaces must comply with
Radius 3.50 in.
320.23. T h e Radius of the Curve 7 X 0.50 in. = 3.50 in.
Author's Comments: • On the Surface of Floor Joists, Rafters, or Studs. In attics and roof spaces that are accessible, substantial guards must protect cables installed across the top of floor joists, or across the face of rafters or studding within 7 ft of floor or floor joists.
T h e radius of the inner edge o f the curve must not be less than 7 times t h e diameter of the cable. Figure 330-4
If this space isn't accessible by permanent stairs or ladders, protection is required only within 6 ft of the nearest edge of the scuttie hole or attic entrance [320.23(A)]. • Along the Side of Framing Members [320,23(B)]. When Type
330.30 Securing and Supporting. (A) General. Type MC cable must be supported and secured by Sta-
MC cable is installed on the side of rafters, studs, or floor
ples, cable ties, straps, hangers, or similar fittings designed and
joists, no protection is required if the cable is installed and
installed so as not to damage the cable.
supported so the nearest outside surface of the cable or
(B) Securing. Type MC cable with four or less conductors sized no
raceway is at Ieast V/A in. from the nearest edge of the framing member where nails or screws are likely to penétrate [300.4(0)].
330.24 Bends.
Figure 330-5 Bends must be made so that the cable won't be
damaged, and the radius of the curve of any bend at the inner edge of the cable must not be less than what's dictated in each of the following instances:
larger than 10 AWG, must be secured within 12 in. of every outlet box, junction box, cabinet, or fitting and at intervals not exceeding 6 ft.
(C) Supporting. Type MC cable must be supported at intervals not exceeding 6 ft. Cables installed horizontally through wooden or metal framing members are considered secured and supported if such support doesn't exceed 6 ft intervals. Figure 330-6 (D) Unsupported Cables. Type MC cable can be unsupported if the cable is:
Mike HolVs lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Metal-ciad Cable (Type MC)
330.80
330.80 Conductor Ampacities.
Conductor ampacity is cal-
M C Cable - Equipment Grounding Conductor
culated on the 90°C insulation rating of the conductors; however, the conductors must be sized to the termination temperature rating in accordance with 110.14{C)(1).
PART III. CONSTRUCTION SPECIFICATIONS 330.108 Equipment Grounding Conductor,
if Type
MC cable is to serve as an equipment grounding conductor, it must comply with 250.118 and 250.122. Author's Comment: The outer sheath of: • Traditional interlocked Type MC cable isn't permitted to serve
: Traditional interlocked T y p e M C cable isn't permitted to serve a s a n equipment grounding i ; conductor, therefore this cable must contain an • equipment g r o u n d i n g conductor in accordance I with 250.118(1).
Figure 330-9
as an equipment grounding conductor, therefore this cable must contain an insulated equipment grounding conductor in accordance with 250.118(1). Figure 330-9 M C Cable E q u i p m e n t G r o u n d i n g Conductor 330.108
• Interlocked Type MC^ cable containing an aluminum grounding/bonding conductor running just below the metal armor is listed to serve as an equipment grounding conductor [250.118(10)(b)]. Figure 330-10 • Smooth or corrugated-tube Type MC cable is listed to serve as an equipment grounding conductor [250.118(10)(c)].
Interlocked Type M C ^ p ® cable containing an aluminum | grounding/bonding conductor running just below the i metal armor is listed to serve a s a n equipment g r o u n d i n g conductor [250.118(10)(b)]. Copynghl 20)1. w w w . M ¡ k e H o « - c o m
Figure 330-10
Mike HaiVs liiustrated Guide to Understanding the 2011 National Electrical Code, Volume
ARTICLE
334
Nonmetallic-Sheathed Cable (Types NM and NMC)
INTRODUCTION TO ARTICLE 334—NONMETALLIC-SHEATHED CABLE (TYPES NM AND NMC) Nonmetallic-Sheathed cable is flexible, inexpensive, and easily installed. It provides very limited physical protection for the conductors, so the instaliation restrictions are strict. Its low cost and relativa ease of instaliation make it a common wiring method for residential and commercial branch circuits. In the field, Type NM cable is typically referred to as "Romex®."
PART I. GENERAL 334.1 Scope.
Nonmetallic-Sheathed Cable (Types N M and N M C Cable) 334.2 Definition
Article 334 covers the use, instaliation, and con-
struction specifications of nonmetallic-sheathed cable.
334.2 Definition. Nonmetallic-Sheathed Cable (Types NM and NMC). A wiring method
^m^NlG
NM-B 600V
that endoses hwo or more insulated conductors, 14 AWG through 2 AWG, within a nonmetallic jacket. •
NM cable has insulated conductors enclosed within an overall nonmetallic jacket.
•
NMC cable has insulated conductors enclosed within an
A wiring m e t h o d that e n d o s e s two, three, or four insulated conductors (14 A W G to 2 A W G ) within a n outer nonmetallic jacket.
overall, corrosión resistant, nonmetallic jacket. Figure
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334-1 Figure 334-1 Author's Comment: It's the generally accepted practice in the electrical industry to cali Type NM cable "Romex®," a registered trademark of the Southwire Ck)mpany.
334.6 Listed. Types NM and
NMC cables must be listed.
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351
334.10
Nonmetallic-Sheathed Cable (Types NM and NMC)
PART II. INSTALLATION 334,10 Uses Permitted.
(2) Multifamily dweilings permitted to be of Types III, IV, and V construction. Figure 334-4
_
Type N M and Type N M C cables can
be used in the following: (1) One- and two-family dweilings of any height, and their attached/ detached garages or storage buildings.
Figures
334-2 and
334^3
N M Cable - O n e - and Two-Family Dweiling Units Section 334.10(1)
N M cable can be installed in multifamily buildings of Type III, IV, a n d V construction.
Figure 334-4
(3) Other structures permitted to be of Types III, IV, and V construction, except as prohibited in 334.12. Cables must be concealed within walls, floors, or ceilings that provide a thermai barrier of material with at Ieast a 15-minute finish rating, as identified in listings of fire-rated assemblies. Figure 334-5
Figure 334-2
N M Cable - Other Structures 334.10(3)
N M Cable - O n e - and Two-Family Dweiling Units 334.10(1)
El
¡LMÍ I
NM cable can be installed in one- and two-family dweiling units and their attached/detached garage or storage buildings.
Figure 334-3
352
In other than dweiling units, N M cable can be installed in Type III, IV, and V construction structures, provided the cables are c o n c e a l e d within a 15-minute finish rating.
Figure 334-5
Mike HolVs lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Nonmetallic-Sheathed Cable (Types NM and NMC)
Author's Comment: See the definition of "Concealed" in Article
334.15
(6) In motion picture studios.
100.
(7) In storage battery rooms. Note 1: Building constructions are defined in NFPA 220-2006, Standard on Types of Building Construction the applicable building code,or both. Note 2: See Annex E for the determination of building types [NFPA 220, Table 3-1].
(8) In hoistways, or on elevators or escalators. (9) Embedded in poured cement, concrete, or aggregate. (10) In any hazardous location, except where permitted by 501.10(6) (3). 502.10(B)(3), and 504.20. (B) Type NM. Type NM cables must not be used under the following
334.12 Uses Not Permitted.
conditions, or in the following locations:
(A) Types NM and NMC.
(1) If exposed to corrosive fumes or vapors. (1) In any dweiling or structure
not specifically
permitted in (2) If embedded in masonry, concrete, adobe, fill, or plaster
334.10(1), (2), and (3). (2) Exposed in dropped or suspended ceilings in other than one- and two-family and multifamily dweilings. Figure 334-6
(3) In a shallow chase in masonry, concrete, or adobe and covered with plaster, adobe, or similar finish. (4) In wet or damp locations. Figure 334-7
N M Cable - S u s p e n d e d Ceilings 334.12(A)(2)
N M Cable - Wet Location 334.12(B)(4)
Direct-Buried Cable or R a c e w a y
Exposed to Weather ^
Concrete in direct contact with earth. VIOLATION
In other than a dweiling unit, N M cable isn't permitted to be run e x p o s e d within a s u s p e n d e d ceiling.
H Figure 3 3 4 ^
VIOLATION Type N M cable isn't suitable for use in wet or d a m p locations. Figure 334-7
Author's Comment: Type NM cable isn't permitted in ducts or cavity plenum spaces [300.22], or for wiring in patient care áreas [517.13].
(3) As service-entrance cable. (4) In commercial garages having hazardous locations, as defined in 511.3. (5) In theaters and similar locations, except where permitted in
334.15 Exposed. (A) Surface of the Building. Exposed Type NM cable must closely follow the surface of the building.
518.4(B).
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353
334.17
Nonmetallic-Sheathed Cable (Types NM and NMC)
(B) Protected from Physical Damage. Nonmetallic-sheathed cable
Type NM cable installed on a wall of an unfinished basement or crawl
must be protected from physical damage by rigid metal conduit, inter-
space subject to physical damage must be protected in accordance
medíate metal conduit, Schedule 80 PVC conduit, Type RTRC-XW con-
with 300.4, or be installed in a raceway with a nonmetallic bushing
duit, electrical metallic tubing, guard strips, or other means approved
or adaptar at the point where the cable enters the raceway, and the
by the authority having jurisdiction.
NM cable must be secured within 12 in. of the point where the cable enters the raceway. Figure 334-9
Author's Comment: When installed in a raceway, the cable must be protected from abrasión by a fitting installed on the end N M Cable Run on Walls Unfinished B a s e m e n t 334.15(0)
of the raceway [300.15(C)]. Type NMC cable installed in shallow chases in masonry, concrete, or adobe, must be protected against nails or screws by a steel píate not
Secure the cable within 12 in. o f t h e raceway.
less than Vie in. thick [300.4{F)] and covered with plaster, adobe, or similar finish.
Type NM cable must be protected in accordance with 300.4 or installed in a raceway that has a nonmetallic bushing or adaptor where the cable enters.
Author's Comment: If Type NM cable is installed in a metal raceway, the raceway isn't required to be connected to an
The cable sheath must extend into the box at Ieast % in.
equipment grounding conductor [250.86 Ex 2 and 300.12 Ex]. (C) In Unfinished Basements and Crawl Spaces. If Type NM cable is installed at angles with joists in unfinished basements and crawl spaces, it's permissible to secure cables containing conductors not
*
^
•
'^^^ metal box must be connected to the EGC.
smaller than two 6 AWG or three 8 AWG conductors directly to the lower edges of the joists. Smaller cables must be installed through
Figure 334-9
bored holes in joists or on running boards. Figure 334-8
334.17 Through or Parallel to Framing Members. N M Cable Run o n Joist Unfinished Basements and Crawl Spaces 334.15(0)
Type N M cable installed through or parallel to framing members or furring strips must be protected against physical damage from penetration by screws or nails by VA in. of separation or by a suitable metal píate [300.4(A) and (0)]. Figures 334^10 and 334-11 If Type N M cable passes through holes in metal studs, a listed bushing or listed grommet is required [300.4(B)(1)] to be in place befare the cable is installed. Figure 334-12
334.23 Attics and Roof Spaces. NM cables sizes 6/2, 8/3, or larger can be mounted directly to the bottom of the joist without protection.
I1
I
Type N M cable installed In
accessible attics or roof spaces must comply with 320.23. Author's Comments: • On the Surface of Floor Joists, Rafters, or Studs. In attics and
Smaller cables must be run through bored holes or they can be mounted to running boards.
roof spaces that are accessible, substantial guards must protect cables installed across the top of floor joists, or across the face of rafters or studding within 7 ft of the floor or floor joists. If this space isn't accessible by permanent stairs or ladders, protection is required only within 6 ft of the nearest edge of the scuttie hole or attic entrance [320.23(A)].
Figure 334-8
354
Mike HoiVs iilustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Nonmetallíc-Sheathed Cable (Types NM and NMC)
N M Cables T h r o u g h W o o d M e m b e r s 334.17
VA
VA
334.30
N M Cable - T h r o u g h Metal Framing 334.17
B o r e d Hole, [300.4(A)(1)] VA in. or More, No Steel Píate Required
B o r e d Hole, [300.4(A)(1)] Less T h a n VA in. j , Steel Píate R e q u i r e d '
Notch {if permitted) [300.4(A)(2)] Steel Píate R e q u i r e d
W h e r e N M cable passes through holes in metal studs, a listed bushing or listed g r o m m e t must be in place before t h e cable is installed.
Copynghl M i l . w«w MikeHoll com
NM cable must be protected against physical damage from penetration by screws or nails by VA in. of separation, o r by a suitable metal píate. Figure 334-10
Figure 334-12
334.24 Bends. When
the cable is bent, it must not be damaged
and the radius of the curve of the inner edge of any bend must not be less than five times the diameter of the cable. Figure 334-13
NM Cables Parallel to Framing M e m b e r s 334.17 [300.4(D)]
"I
Framing Member
A Sharp bend is a c o m m o n VIOLATION.
Con-ect Bending Radius
N M Cable - Bending Radius 334.24 Begin
Cable must be at Ieast VA in. from t h e nearest edge of a framing m e m b e r or be protected by a steel píate or sieeve.
I
I
I Radius 2.50 in.
• Steel Píate for N o t c h e s | in W o o d [300.4(A)(2)]
11 I
'
1
T h e Radius of the Curve 5 X 0.50 in. = 2.50 in. Copyrtghl 2011. www Mlk.HoH com
T h e radius of the inner edge of the curve must not be less than 5 times the diameter of the cable. Figure 334-13 Figure 334-11
334,30 Securing and Supporting. Along the Side of Framing Members [320.23(6]]. When Type NM cable is installed on the side of rafters, studs, or floor joists, no protection is required if the cable is installed and supported so the nearest outside surface of the cable or raceway is at Ieast V/A in. from the nearest edge of the framing member if nails or screws are likely to penétrate [300.4(D)].
staples, straps, cable
ties, hangers, or similar fittings must secure Type NM cable in a manner that won't damage the cable. Type NM cable must be secured within 12 in. of every box, cabinet, enclosure, or termination fitting, except as permitted by 314.17(C) Ex or 312.5(0) Ex, and at intervals not exceeding AVA ft.
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355
Nonmetallic-Sheathed Cable (Types NM and NMC)
334.80
Two-wire (fíat) Type NM cable isn't permitted to be stapled on edge. Figure 334-14
N M Cable - Securing a n d Supporting 334.30
N M Cable - Support 334.30 Cable ties can be used to secure N M cables.
Type N M cable must be secured a n d supported within 12 in. of termination or fitting a n d at intervals not e x c e e d i n g 4 1/2 ft.
T w o cables are permitted t o be s e c u r e d by o n e staple. Type N M cable installed in a raceway isn't required to be secured within the raceway.
VIOLATION N M cables must not be stapled o n e d g e .
CopyiigM 2011. www.Mikahlaa.com
Type N M cable must be secured within 12 i n . of tennination a n d at intervals not e x c e e d i n g 4V2 ft.
Figure 334-15
Figure 334-14 N M Cable - Horizontal Support 334.30(A) Type NM cable installed in a raceway isn't required to be secured within the raceway. Figure 334-15 (A) Horizontal Runs. Type NM cable installed horizontally in bored
Max. 4V2ft Between Framing Members
Vú
or punched holes in wood or metal framing members, or notches in wooden members is considered secured and supported, but the cable must be secured within 1 ft of termination. Figure 334-16 Note: See 314.17(C) for support where nonmetallic boxes are used. (B) Unsupported. Type NM cable can be unsupported in the following situations: (1) If Type NM cable is fished between concealed access points in finished buildings or structures, and support is impracticable.
N M cable run horizontally through framing m e m b e r s is considered supported if s e c u r e d within 1 ft of termination. Figure 334-16
(2) Not more than AV? ft of unsupported cable is permitted from the last point of support within an accessible ceiling for the connec-
334.80 Conductor Ampacity.
tion of luminaires or equipment.
lated on the 90°C insulation rating of the conductor in accordance
Conductor ampacity is caicu
with Table 310.15(B)(16), however the conductors must be sized to Author's Comment: Type NM cable isn't permitted as a
the termination temperature rating of 60°C.
wiring method above accessible ceilings, except in dweilings [334.12(A){2)].
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Mike Hoit's Iliustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Nonmetallic-Sheathed Cable (Types NM and NMC)
334.80
Question: Wtiat size Type NM cable is required to supply a 9.60
If múltiple Type NM cables pass through the same wood framing
'i^K 240V, single-phase fixed space heater with a 3A blower
opening that's to be sealed with thermai insulation, caulking, or
wtof? The termináis are rated 75%. Figure 334-17
sealing foam, the allowable ampacity of each conductor must be adjusted in accordance with Table 310.15(B)(3)(a). Figure 334-18
(aj2AWG
(b)4AWG
(c)6AWG
(d)8AWG
Answer: (b) 4 AWG N M Cable - Conductor A m p a c i t y 334.80
Step 1: Determine the total load in amperes: l = VA/E I = 9mW/240V-h
3A
l = 40A-h3A l = 43A Step 2: Conductor and Protection Size [424.3(8)]. Size the ungrounded conductors and overcurrent device at no
W h e r e N M cables pass through t h e s a m e w o o d framing opening to be sealed with caulk or sealing f o a m , the ampacity of each conductor must be adjusted in accordance with Table 310.15(B)(3){a) based o n the 90°C ampacity c o l u m n of Table 310.15(B)(16).
less than 125 percent of the total heating load. Conductor/Protection Size = Loadx 1.25 Conductor/Protection Size = 43A x 1.25 Conductor/Protection Size = 53.75A According to Table 310.15(B)(16), a 6AWG conductor rated 55A at 60% protected with a 60A overcurrent device [240.6(A)].
Figure 334-18
NM Cable - Conductor Ampacity 334.80 9.6kW Heat 3AFan
Author's Comment: This requirement has no effect on conductor sizing if you bundie no more than nine current-carrying 14
(40A + 3A) = 4 3 A 4 3 A x 1.25 = 53.75A 6 A W G Rated 5 5 A at 60°C
or 12 AWG conductors together. For example, three 14/2 cables and one 14/3 cable (nine current-carrying 1 4 THHN conductors) are bundied together in a dry location, the ampacity for each conductor (25A at 90°C, Table 310.15(B)(16)) is adjusted by a
Copyright
Conductors are sized to the 60°C column rating of Table 31Q.15fB)(16)
70 percent adjustment factor [Table 310.15(B)(3)(a)]. Adjusted Conductor Ampacity = 25A x 0.70 Adjusted Conductor Ampacity ^ 17.50A
Figure 334-17
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357
334.100
Nonmetallic-Sheathed Cable (Types NM and NMC)
PART III. CONSTRUCTION SPECIFICATIONS 334.100 Construction.
334.108 Equipment Grounding Conductor.
Type NM
cable must have an insulated, covered, or bare equipment groundThe outer cable sheath of Type N M
ing conductor.
cable must be constructed with nonmetallic material.
334.104 Conductors. The
conductors must be 14 AWG through
334.112 Insulation.
N M conductor insulation must be rated
90°Ct194°F).
2 AWG copper, or 12 AWG through 2 AWG aluminum or copper-clad aluminum.
358
Note: Types NM cable identified by the markings NM-B meet this requirement.
Mike HolVs lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
ARTICLE
338
Service-Entrance Cable (Types SE and USE)
INTRODUCTION TO ARTICLE 338—SERVICE-ENTRANCE CABLE (TYPES SE AND USE) Sen/ice-entrance cable is a single conductor or muíticonductor assembiy with or without an overall moisture-resistant covering. This cable is used primarily for services not over GOOV, but can aiso be used for feeders and branch circuits when the limitations of this article are observed.
PART L GENERAL 338.1 Scope.
Type SE. SE and SER cables have a flame-retardant, moisture-resistant covering and are permitted only in aboveground installations.
Article 338 covers the use, instaliation, and con-
struction specifications of service-entrance cable, Types SE and USE.
338.2 Definitions.
These cables are permitted for branch circuits or feeders when installed in accordance with 338.10(8). Author's Comment: SER cable is SE cable with an insulated
Service-Entrance Cable. Service-entrance cable is a single or muíti-
neutral, resulting in three insulated conductors with an uninsu-
conductor assembiy, with or without an overall covering, used primar-
lated equipment grounding conductor. SER cable is round, while
ily for services not over eoov. Figure 338-1
2-wire SE cable is fíat. Type USE. USE cable is identified as a wiring method permitted for
Service-Entrance Cable 338.2 Definition A single or muíticonductor assembiy with o r without an overall covering used primarily for services not over 600V.
underground use; its covering is moisture resistant, but not fíame retardan!. Author's Comment: USE cable isn't permitted to be installed indoors [338.10(B)], except single-conductor USE dual rated as
Aboveground
SE cable is permitted only in a b o v e g r o u n d installations and is permitted for branch circuits or feeders w h e n installed according to 338.10ÍB).
RHH/RHW.
PART II. INSTALLATION 338.10 Uses Permitted.
Underground Only (A) Service-Entrance Conductors. Service-entrance cable used as service-entrance conductors must be installed in accordance with Article 230. USE cable is identified for underground use. Its covering is moisture resistant but not fíame retardant, and it isn't suitable for use within a premises. Figure 338-1
(B) Branch CircuJts or Feeders. (1) Insulated Conductor. Type SE service-entrance cable is permitted for branch circuits and feeders where the circuit conductors are insulated.
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Service-Entrance Cable (Types SE and USE)
338.12
(2) Uninsulated Conductor. SE cable is permitted for branch circuits
The máximum conductor temperature rating can be used [310.15(6)
and feeders if the insulated conductors are used for circuit wiring,
(2)] for ampacity adjustment and correction purposes, but when
and the uninsulated conductor is only used for equipment grounding
installed in thermai insulation the conductors must be sized in
purposes. Figure 338-2
accordance with Table 310.15(B)(16) 60°C rated conductor column. CAUTION:
g
S E Cable - Use of Ur^insulated Conductor
Underground
service-entrance
cable
(USE) is not permitted for interior wiring because it does not have a flame-retardant insulation. It would only be permitted in interior wiring when dual listed as wire type in accordance with Table 310.104, such as RHW. (b) Exterior Installations. The cable must be supported in accordance with 334.30 and where run underground the cable must comply with Part II of Article 340.
338.12 Uses Not Permitted. (A) Service-Entrance Cable. SE cable isn't permitted under the folSE and SER cable can be used for branch circuits and feeders, but the uninsulated conductor can only be used for equipment grounding.
lowing conditions or locations: (1) If subject to physical damage unless protected in accordance with
Copyngh'. 2011. «wwMiiieHod com
230.50(A). Figure 338-2 (2) Underground with or without a raceway. Ex: In existing Installations, uninsulated conductors may be used for the neutral conductor if the uninsulated neutral conductor of the cable originates in service equipment. (3) Temperature Limitations. SE cable must not be subjected to
(B) Underground Service-Entrance Cable. USE cable isn't permitted: (1) For interior wiring. (2) Above ground, except where protected against physical damage in accordance with 300.5(0).
conductor temperatures exceeding its insulation rating. (4) Instaliation Methods for Branch Circuits and Feeders. SE cable used for branch circuits or feeders must comply with (a) and (b).
338.24 Bends.
Bends in cable must be made so the protective
coverings of the cable aren't damaged, and the radius of the curve of the inner edge is at Ieast five times the diameter of the cable.
(a) Interior Installations. SE cable used for interior branch circuit or feeder wiring must be installed in accordance with the same requirements as Type NM Cable—Article 334, excludinq 334.80.
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Mike HoiVs Iilustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Underground Feeder and Branch-Circuit Cable (Type UF)
ARTICLE
340
INTRODUCTION TO ARTICLE 340--UNDERGR0UND FEEDER AND BRANCH-CIRCUIT CABLE (TYPE UF) UF cable is a moisture-, fungus-, and corrosion-resistant cable suitable for direct burial in the earth.
PART I. GENERAL
Author's Comments:
340.1 Scope.
• UF cable is a moisture-, fungus-, and corrosion-resistant
Article 340 covers the use, instaliation, and con-
struction specifications of underground feeder and branch-circuit
cable suitable for direct burial in the earth. It comes in sizes 1 4 AWG through 4 / 0 AWG [340.104]. The covering of muíti-
cable, Type UF
conductor Type UF cable is molded plástic that encases the insulated conductors.
340.2 Definition.
• Because the covering of Type UF cable encapsulates the insuUnderground Feeder and Branch-Circuit
Cable (Type UF). A factory
lated conductors, it's difficult to strip off the outer jacket to
assembiy of insulated conductors with an integral or an overall cov-
gain access to the conductors, but this covering provides
ering of nonmetallic material suitable for direct burial in the earth.
excellent corrosión protection. Be careful not to damage the
Notice that Type UF is not allowed as a service cable. Figure 340-1
conductor insulation or cut yourself when you remove the outer cover.
Underground Feeder a n d Branch-Circuit C a b l e Type U F Cable 340.2. Definition
340.6 Listing Requirements.
Type UF cable must be lísted.
PART II. INSTALLATION 340.10 Uses Permitted. (1) Underground, in accordance with 300.5. (2) As a single conductor in the same trench or raceway with circuit conductors. A factory assembiy of insulated conductors with an integral or a n overall covering of nonmetallic material suitable for direct burial in t h e earth. Copyright 2011.
(3) As interior or exterior wiring in wet, dry, or corrosive locations. (4) As Type NM cable, when installed in accordance with Article 334.
>«ww.Mik«Hon com
(5) For solar photovoltaic systems, in accordance with 690.31. Figure 340-1 (6) As single-conductor cables for nonheating leads for heating cables, as provided in 424.43. (7) Supported by cable trays.
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361
Underground Feeder and Branch-Circuít Cable (Type UF)
340.12
Uses Not Permitted.
Author's Comment: UF cable isn't permitted in ducts or cavity plenum spaces [300.22], or in patient care áreas [517.13].
(1) As services [230.43]. (2) In commercial garages [511.3].
Bends.
340i24
Bends in cables must be made so that the pro-
tective coverings of the cable aren't damaged, and the radius of the
(3) In theaters [520.5].
curve of the inner edge must not be less than five times the diame(4) In motion picture studios [530.11],
ter of the cable.
(5) In storage battery rooms [Article 480]. (6) In hoistways [Article 620]. (7) In hazardous locations, except as specifically permitted by other
340.80
Ampacity.
The ampacity of conductors contained in UF
cable is based on the 60°C insulation rating listed in Table 310.15(B) (16).
articles in the Code. 340.112
(8) Embedded in concrete.
insulation.
The conductors of UF cable must be one
of the moisture-resistant types listed in Table 310.104(A) suitable for
(9) Exposed to direct sunlight unless identified. (10) If subject to physical damage. Figure 340-2
branch-circuit wihng. If installed as a substitute wiring method for Type NM cable, the conductor insulation must be rated 90°C (194°F).
(11) As overhead messenger-supported wiring.
UF Cable - Physical Protection 340.12(10)
UF Cable can't be used w h e r e subject to physical d a m a g e .
Figure 3 4 0 - 2
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Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
ARTICLE
342
ntermediate Metal Conduit (Type IMC)
INTRODUCTION TO ARTICLE 342—INTERMEDIATE METAL CONDUIT (TYPE IMC) Intermedíate metal conduit (IMC) is a circular metal raceway with an outside diameter equal to that oí rigid metal conduit. The wall thickness of intermedíate metal conduit is less than that of rigid metal conduit (RMC), so it's a greater interior cross-sectional área for containing conductors. Intermedíate metal conduit is lighter and less expensive than rigid metal conduit, but it can be used in all of the same locations as rigid metal conduit. Intermedíate metal conduit aiso uses a different steel alloy that makes it stronger than rigid metal conduit, even though the walls are thinner. Intermedíate metal conduit is manufactured in both galvanized steel and aluminum; the steel type is much more common.
PART I. GENERAL 342.1 Scope,
Author's Comment: The type of steel from which intermedíate metal conduit is manufactured, the process by which it's made,
Article 342 covers the use, instaliation, and con-
struction specifications of intermedíate metal conduit and associated
and the corrosión protection applied are all equal, or superior, to that of rigid metal conduit.
fittings.
342.6 Listing Requirements.
342.2 Definition,
intermedíate metal conduit and
its associated fittings, such as elbows and couplings, must be listed. Intermedíate Metal Conduit (Type IMC). A listed steel raceway of circular cross section that can be threaded with integral or associated couplings. It's listed for the instaliation of electrical conductors, and is used with listed fittings to provide electrical continuity. Figure 342-1
PART II. INSTALLATION 342.10 Uses Permitted. (A) All Atmospheric Conditions and Occupancies. Intermedíate
Intermedíate Metal Conduit (Type IMC) 342.2 Definition
metal conduit ís permitted in all atmospheric
conditions and
occupancies. (B) Corrosión Environments. Intermedíate metal conduit, elbows, couplings, and fittings can be installed ín concrete, in direct contact with the earth, or ín áreas subject to severe corrosivo influences if A listed steel circular raceway that can be threaded with integral or associated couplings. Compression
Set S c r e w
provided with corrosión protection and judged suitable for the condition in accordance with 300.6. (C) Cinder Fill. IMC can be installed ín or under cinder fill subject to permanent moisture when protected on all sides by 2 ín. of non-
\ : \
_,.„^ti Threadless IMC Fittings
cínder concrete; where the conduit isn't less than 18 ín. under the fill; or where protected by corrosión protection judged suitable for the condition.
CopyngM 2011. www UikeHoll con)
Figure 342-1
mkB
Holt Enterprises, Inc. • www.MikeHolt.com • 888.NEC.C0DE (632.2633)
363
342.14
Intermedíate Metal Conduit (Type IMC)
(D) Wet Locations. Support fittings, such as screws, straps, and so
Author's Comment: See 300.17 for additional examples on
forth, installed in a wet location must be made of corrosion-resistant
how to size raceways when conductors aren't all the same size.
material, or be protected by corrosion-resistant coatings in accorCables can be installed in intermedíate metal conduit, as long as the
dance with 300.6.
number of cables doesn't exceed the allowable percentage fill speciCAUTION: Supplementary
coatings
for corrosión
fied I n T a b l e l , Chapter 9.
protection haven't been investigated by a product testing and listing agency and these coatings are
342.24 Bends.
Raceway bends must not be made in any manner
known to cause cáncer in laboratory animáis. There's a docu-
that would damage the raceway, or significantly change its internal
mented case where an electrician was taken to the hospital
diameter (no kinks). The radius of the curve of the inner edge of any
for lead poisoning añer using a supplemental coating product
field bend must not be less than shown in Table 2, Chapter 9.
(asphalted paint) in a poorly ventilated área As with all prodinstructions,
Author's Comment: This is usually not a probiem, because
inciuding material data safety sheets, particularly when petro-
benders are made to comply with this table. However, when
ucts, be sure to read and follow all product
leum-based chemicals (volatile organic compounds) may be
using a hickey hender (short-radius hender), be careful not to
in the material.
over-bend the raceway.
342.14 Dissimilar Metals.
If practical, contact with dissimi-
342.26 Number of Bends (360°).
To reduce the stress
lar metáis should be avoided to prevent the deterioration of the metal
and friction on conductor insulation, the máximum number of bends
because of galvanic action. Aluminum fittings and enclosures, how-
(inciuding offsets) between pulí points must not exceed 360°. Figure
ever, are permitted with steel intermedíate metal conduit.
342-2
342.20 Trade Size. IMC - N u m b e r of Bends 342.26
(A) Minimum. Intermedíate metal conduit smaller than trade size Vi must not be used. (B) Máximum. Intermedíate metal conduit larger than trade size 4
90°
must not be used.
To reduce the stress a n d friction on conductor insulation, the total amount of bends (inciuding offsets) between pulí points can't e x c e e d 3 6 0 ° .
342.22 Number of Conductors. The number of conductors in IMC isn't permitted to exceed the percentage fill specified in Table
There's n o m á x i m u m distance b e t w e e n pulí points.
1, Chapter 9. Raceways must be large enough to permit the instaliation and removal of conductors without damaging the conductor insulation. When all conductors in a raceway are the same size and
Pulí Points
insulation, the number of conductors permitted can be found in Annex Copyrtgnt 2011, www.l*lteHofl.com
Cfor the raceway type.
Figure 342-2 Question: How many 10 THHN conductors can be installed in trade size 11MC? (a) 12
(b) 14
(c) 16
18
Author's Comment There's no máximum distance between pulí boxes because this is a design issue, not a safety issue.
Answer: (d) 18 conductors [Annex C, Table C4]
342.28 Reaming.
When the raceway is cut in the field, reaming
is required to remove the burrs and rough edges.
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Mike HolVs lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Intermedíate Metal Conduit (Type IMC)
342.30
Auttior's Comment: It's a commonly accepted practice to ream small raceways with a screwdriver or the backside of pliers.
IMC - Secureiy Fastened to Structural Members 342.30(A)(2l
However, when the raceway is cut with a three-wheel pipe cutter, a reaming tool is required to remove the sharp edge of the indented raceway. When conduits are threaded in the field, the threads must be coated with an eiectrically conductive, cor-
Coupling is O k a y
Secured
rosion-resistant compound approved by the authority having jurisdiction, in accordance with 300.6(A).
342.30 Securing and Supporting.
Máximum 5ft
intermedíate metal
conduit must be installed as a complete system in accordance with 300.18 [300.10 and 300.12], and it must be secureiy fastened in
Máximum 5ft
W h e r e structural m e m b e r s don't permit fastening within 3 ft of termination, it must be secured within 5 ft.
place and supported in accordance with (A) and (B). Copyngnt 2011
(A) Secureiy Fastened. IMC must be secured in accordance with one Figure 342-4
ofthe following: (1J Fastened within 3 ft of each outlet box, junction box, device box, cabinet, conduit body, or other conduit termination. Figure 342-3
(B) Supports. (1) General. Intermedíate metal conduit must generally be supported at intervals not exceeding 10 ft. (2) Straight Horizontal Runs. Straight horizontal runs made with
IMC - Secureiy Fastened
threaded couplings can be supported ín accordance with the dis-
342.30(A)Ca 3ft Termination
3ft Termination
tances lísted in Table 344.30{B)(2). Figure 342-5
A I M C - Support of Straight R u n s 342.30{B){2) Trade Size 1 I M C Table 344.30(B)(2) 12 ft B e t w e e n Supports
Intermedíate metal conduit must be secureiy fastened within 3 ft of every box, cabinet, or termination fitting.
C o p y n ^ 301 \. Mnn>MikeHo«.com
Figure 342-3
Author's Comment: Fastening is required within 3 ft of termi-
3fl
12ft
12ft
Straight horizontal runs m a d e with threaded couplings can be supported in a c c o r d a n c e with the distances listed in Table 344.30(B)(2).
nations, not within 3 ft of each coupling. CotiyógM 2011, ww*.M*oHolt.co(n
¡2) When structural members don't permit the raceway to be secured
Figure 342-5
within 3 ft of a box or termination fitting, the raceway must be secured within 5 ft of the termination. Figure 342-4 ^
Conduits aren't required to be secureiy fastened within 3 ft of the service head for an above-the-roof termination of a mast.
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365
Intermedíate Metal Conduit (Type IMC)
342.42
Author's Comment: IMC must be provided with expansión fit-
Table 344.30(B)(2) Trade Size
tings if necessary to compénsate for thermai expansión and
Support Spacing lOft
1
contraction [300.7{B)]. The expansión characteristics for metal raceways are determined by multipiying the valúes from Table 352.44 by 0.20, and the expansión characteristics for aluminum
i 2 r
raceways is determined by multipiying the valúes from Table
14ft
352.44 by0.40 [300.7 Note].
VA~V/? 2 - 2V7
16ft
3 and larger
20 ft
(3) Vertical Rlsers. Exposed vertical risers for fixed equipment can be supported at intervals not exceeding 20 ft, if the conduit is made up with threaded couplings, firmiy supported, secureiy fastened at the top and bottom of the riser, and if no other means of support is available. Figure 342-6
342.42 Couplings and Connectors. (A) Instaliation. Threadless couplings and connectors must be made up tight to maintain an effective ground-fault current path to safely conduct fault current in accordance with 250.4(A)(5), 250.96(A), and 300.10. Author's Comment: Loóse locknuts have been found to bum clear before a fault was cleared because loóse termination fit-
IMC - Support of Vertical Risers 342.30{B)(3}
tings increase the impedance of the fault current path. If buried in masonry or concrete, threadless fittings must be the concrete-tight type. If installed in wet locations, fittings must be listed for use in wet locations in accordance with 314.15(A). Threadless couplings and connectors must not be used on threaded
H H
Exposed vertical risers c a n be supported at intervals not exceeding 20 ft if firmiy supported and secured at t h e top and bottom of the riser.
Upto 2 0 ft
conduit ends unless listed for the purpose. (B) Running Threads. Running threads aren't permitted for the connection of couplings, but they're permitted at other locations. Figure 342-7
IMC - Running Threads 342A2{B) C C f i y r ^ 2011.
Running Thread Figure 342-6 Okay Between Boxes or Enclosures
T h r e a d e d Coupling
r/
(4) Horizontal Runs. Conduits installed horizontally in bored or punched holes in wood or metal framing members, or notches in wooden members are considered supported, but the raceway must be secured within 3 ft of termination.
B iw
I VIOLATION
Copyright 2011. www.MlkeHon.com
Running threads aren't permitted for the connection of couplings, but they are permitted at other locations. Figure 342-7
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fñlke Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Intermedíate Metal Conduit (Type IMC)
342.46 Bushings.
342.46
IMC - Bushings 342.46 Note Fitting Termination
l o protect conductors from abrasión, a metal
or plástic bushing must be installed on conduit terminahon threads, regardiess of conductor size, unless the box, fitting, or enclosure is
Threaded Termination
Hub or Boss Termination
designed to provide this protection. Note: Conductors 4 AWG and larger that enter an enclosure must be protected from abrasión, during and after instaliation, by a fitting that provides a smooth, rounded, insulating surface, such as an insulating bushing, unless the design of the box, fitting, or enclosure provides equivalent protection, in accordance with 300.4{G). Figure 342-« A n y Size Conductor Bushing Required
4 AWG a n d Larger Bushing Required
6 AWG and Smaller Bushing Not Required
A n y Size Conductor Bushing Not Required
Conductors 4 A W G a n d larger must b e protected by a fitting that provides a s m o o t h , r o u n d e d , insulating surface, s u c h a s an insulating bushing [300.4(G)]. Figure 342-8
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367
ARTICLE
Rigid Metal Conduit (Type RMC)
344
INTRODUCTION TO ARTICLE 344—RIGID METAL CONDUIT (TYPE RMC) Rigid metal conduit, commonly called "rigid," has long been the standard raceway for providing protection from physical impact and from difficult environments. The outside diameter of rigid metal conduit is the same as intermedíate metal conduit. However, the wall thickness of rigid metal conduit is greater than intermedíate metal conduit; therefore it's a smaller interior cross-sectional área. Rigid metal conduit is heavier and more expensive than intermedíate metal conduit, and it can be used in any location. Rigid metal conduit is manufactured in both galvanized steel and aluminum; the steel type is much more common.
PART I. GENERAL 344.1 Scope.
Author's Comment: When the mechanical and physical characteristics of rigid metal conduit are desired and a corrosive
Article 344 covers the use, instaliation, and con-
struction specifications of rigid metal conduit and associated fittings.
environment is anticipated, a PVC-coated raceway system is commonly used. This type of raceway is frequently used in the petrochemical industry, The common trade ñame of this coated
344.2 Definition.
raceway is "Plasti-bond®," and it's commonly referred to as "Rob
Rigid Metal Conduit (Type HMC). A listed metal raceway of circular cross section with integral or associated couplings, listed for the instaliation of electrical conductors, and used with listed fittings to provide electrical continuity. Figure 344-1
Roy conduit." The benefits of the improved corrosión protection can be achieved only when the system is properiy installed. Joints must be sealed in accordance with the manufacturer's instructions, and the coating must not be damaged with tools such as benders, pliers, and pipe wrenches. Couplings are available with an extended skirt that can be properiy sealed after instaliation.
Rigid Metal Conduit (Type R M C ) 344.2 Definition
344.6 Listing Requirements.
Rlgld metal conduit, elbows,
couplings, and associated fittings must be listed.
A listed metal circular raceway that c a n be threaded with integral or associated couplings. Compression
Set Screw
PART II. INSTALLATION 344.10 Uses Permitted. (A) Atmospheric Conditions and Occupancies. (1) Galvanized Steel and Stainless Steel. Galvanized steel and
Threadless R M C Fittings Copynghl 2011,
Figure 344-1
«WH.lAkeHoH oom
stainless steel rigid metal conduit is permitted in all atmospheric conditions and occupancies. (2) Red Brass. Red brass rigid metal conduit is permitted for direct burial and swimming pool applications.
368
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Rigid Metal Conduit (Type RMC)
344.26
(3) Aluminum. Rigid aluminum conduit is permitted if judged suitable for the environment.
Question: How many 8 THHN conductors can be installed in trade size V/zRfi/IC?
(B) Corrosión Environments.
(a) 16
(1) Galvanized Steet and Stainless Steel. Rigid metal conduit fit-
(b)18
(c)20
(d)22
Answer: 22 conductors [Annex C, Table C8]
tings, elbows, and couplings can be installed in concrete, in direct contact with the earth, or in áreas subject to severe corrosive influences judged suitable for the condition.
Author's Comment: See 300.17 for additional examples on
(2) Aluminum. Rigid aluminum conduit must be provided with sup-
how to size raceways when conductors aren't all the same size.
plementary corrosión protection approved by the authority having jurisdiction if encased in concrete or in direct contact with the earth.
Cables can be installed in rigid metal conduit, as long as the number
(C) Cinder FUI. Galvanized steel, stainless steel, and red brass RMC
Table 1, Chapter 9.
of cables doesn't exceed the allowable percentage fill specified in is permitted in or under cinder fill subject to permanent moisture, when protected on all sides by a layer of noncinder concrete not less
344.24 Bends. Raceway
than 2 in. thick; where the conduit isn't less than 18 in. under the
that would damage the raceway, or significantly change its internal
bends must not be made in any manner
fill; or where protected by corrosión protection judged suitable for the
diameter (no kinks). The radius of the curve of the inner edge of any
condition.
field bend must not be less than shown in Table 2, Chapter 9.
• -1>-
(D) Wet Locations. Support fittings, such as screws, straps, and so forth, installed in a wet location must be made of corrosion-resistant material or protected by corrosion-resistant coatings in accordance with 300.6.
Author's Comment: This is usually not a probiem because benders are made to comply with this table, However, when using a hickey hender (short-radius hender), be careful not to over-bend the raceway.
/ \: Supplementary coatings (asphalted paint) for corrosión protection haven 't t}een investigated by
344.26 Number of Bends (360'').
a product testing and listing agency and these coat-
and friction on conductor insulation, the máximum number of bends
ings are known to cause cáncer in laboratory animáis.
To reduce the stress
(inciuding offsets) between pulí points must not exceed 360°. Figure 344-2
344.14 Dissimilar Metals.
If practical, contact with dissimi-
lar metáis should be avoided to prevent the deterioration of the metal R M C - N u m b e r of B e n d s 344.26
because of galvanic action. Aluminum fittings and enclosures are permitted, however, with rigid metal conduit.
344.20 Trade Size.
90° To reduce t h e stress and friction on conductor insulation, the total a m o u n t of bends (inciuding offsets) between pulí points can't e x c e e d 360o.
(A) Mínimum. Rigid metal conduit smaller than trade size ¥2 must not be used. (B) Máximum. Rigid metal conduit larger than trade size 6 must not
150
be used.
344.22 Number of Conductors.
90°
There's no m á x i m u m distance b e t w e e n pulí points. Raceways must be large
— P u l í
enough to permit the instaliation and removal of conductors without
Points
\r—-^^
15°
o o
damaging the conductors' insulation. When all conductors in a raceway are the same size and insulation, the number of conductors permitted can be found in Annex C for the raceway type.
Figure 344-2
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369
344.28
Rigid Metal Conduit (Type RMC)
Author's Comment: There's no máximum distance between
Author's Comment: Fastening is required within 3 ft of termi-
pulí boxes because this is a design issue, not a safety issue.
nations, not within 3 ft of each coupling.
344.28 Reaming.
• When structural members don't permit the raceway to be When the raceway is cut in the field, reaming
is required to remove the burrs and rough edges.
secured within 3 ft of a box or termination fitting, the raceway must be secured within 5 ft of the termination. Figure 344-4
Author's Comment: It's a commonly accepted practice to ream small raceways with a screwdriver or the backside of
• Conduits aren't required to be secureiy fastened within 3 ft of the service head for an above-the-roof termination of a mast.
pliers. However, when the raceway is cut with a three-wheel pipe cutter, a reaming tool is required to remove the sharp edge of the indented raceway. When conduit is threaded in the field, the threads must be coated with an eiectrically conductive, cor-
R M C - Secureiy Fastened to Structural M e m b e r s 344.30(A)
rosion-resistant compound approved by the authority having jurisdiction, in accordance with 300.6(A).
344.30 Securing and Supporting.
^
Rígid metal conduit
*
*
*
Coupling is O k a y
%
*
; Secured
must be installed as a complete system in accordance with 300.18 [300.10 and 300.12], and it must be secureiy fastened in place and Máximum 5ft
supported in accordance with (A) and (B).
Máximum 5ft
(A) Secureiy Fastened. RMC must be secured in accordance with one of the following: Figure 344-3 •
W h e r e structural m e m b e r s don't permit fastening within 3 ft of termination, it must be secured within 5 ft.
Fastened within 3 ft of each outlet box, junction box, device box, cabinet, conduit body, or other conduit termination.
Copyright 2011,
ww*.M*eHoir com
Figure 344-4 R M C - Secureiy Fastened 344.30(A) (B) Supports. 3ft Termination
3ft Termination
(1) General. Rigid metal conduit must be supported at intervals not exceeding l O f t . (2) Straight Horizontal Runs. Straight horizontal runs made with threaded couplings can be supported in accordance with the distances listed in Table 344.30(B)(2). Figure 344-5
Rigid metal conduit must be secureiy fastened within 3 ft of every box, cabinet, or termination fitting.
Table 344.30(B)(2) Trade Size
Support Spacing lOft
Copynghl 2011.
www MiUHoll com
12 ft* Figure 344-3
370
iy4-iK2
14ft
2-2^/2
16ft
3 and larger
20 ft
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Rigid Metal Conduit (Type RMC)
R M C - Support of Straight Runs 344.30(B)(2) Trade Size 1 R M C Table 344.30(B)(2) 12 ft Between Supports
344.42
Author's Comment: Rigid metal conduit must be provided with expansión fittings if necessary to compénsate for thermai expansión and contraction [300.7(B)]. The expansión characteristics for metal raceways are determined by multipiying the valúes from Table 3 5 2 . 4 4 by 0.20, and the expansión characteristics for aluminum raceways is determined by multipiying the valúes from Table 3 5 2 . 4 4 by 0 . 4 0 [300.7 Note].
344.42 Couplings and Connectors. Straight horizontal runs m a d e with threaded couplings can be supported in a c c o r d a n c e with the distances listed in Table 344.30(B)(2). C o p y l ^ 2011. vrww.MtaHcK.ixMn
i
Figure 344-5
(A) Instaliation. Threadless couplings and connectors must be made up tight to maintain an effective ground-fault current path to safely conduct fault current in accordance with 250.4(A)(5), 250.96{A), and 300.10. Author's Comment: Loóse locknuts have been found to burn clear before a fault was cleared because loóse connections
(3) Vertical Risers. Exposed vertical nsers for fixed equipment can be supported at intervals not exceeding 20 ft, if the conduit is made up with threaded couplings, firmiy supported, secureiy fastened at the top and bottom of the riser, and if no other means of support is available. Figure 344-6
increase the impedance of the fault current path.
If buried in masonry or concrete, threadless fittings must be the concrete-tight type. If installed in wet locations, fittings must be listed for use in wet locations, in accordance with 314.15(A). Threadless couplings and connectors must not be used on threaded conduit ends, unless listed for the purpose.
R M C - Support of Vertical Risers 344.30(B)(3)
(B) Running Threads. Running threads aren't permitted for the connection of couplings, but they're permitted at other locations. Figure 344-7
T h r e a d e d Coupling R M C - Running T h r e a d s 344.42(B)
Exposed vertical risers c a n be supported at intervals not exceeding 20 ft if firmiy supported and secured at the top and bottom of the riser.
Okay Between Boxes Or Enclosures
T h r e a d e d Coupling
Copyright 2011, wwwMkeHon.com
VIOLATION
Figure 344-6 Copyright 2011. www.MIkeHoncoir
Running threads aren't permitted for the connection of couplings. but they are permitted at other locations. (4) Horizontal Runs. Conduits installed horizontally in bored or punched holes in wood or metal framing members, or notches in
Figure 344-7
wooden members, are considered supported, but the raceway must be secured within 3 ft of termination.
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344.46
344.46 Bushings.
Rigid IVIetal Conduit (Type RMC)
R M C - Bushing Requirements 344.46 Note
To protect conductors from abrasión, a meta!
or plástic bushing must be installed on conduit threads at terminations, regardiess of conductor size, unless the box, fitting, or enclo-
Threaded Termination
, I
Fitting Termination
, Hub or Boss | Termination
sure is designed to provide this protection. Note: Conductors 4 AWG and larger that enter an enclosure must be protected from abrasión, dunng and after instaliation. by a fitting that provides a smooth, rounded, insulating surface, such as an insulating bushing, unless the design of the box, fitting, or enclosure provides equivalent protection, in accordance with 300.4{G). Figure 344-8
PART III. CONSTRUCTION SPECIFICATIONS 344.130 Standard Lengths.
The standard length of RMC is
10 ft inciuding an attached coupling, and each end must be threaded. Longer or shorter lengths with or without a coupling and threaded or unthreaded are permitted.
372
A n y Size Conductor Bushing Required
| 4 AWG | a n d Larger Bushing Required
6 AWG ¡ Any Size and Smaller ! Conductor Bushing Not Bushing Not Required Required
Copyoght 2011, www.M^.Mott com
Conductors 4 A W G and larger must be protected by a fitting that provides a s m o o t h , r o u n d e d , insulating surface, such a s an insulating bushing [300.4(G)]. Figure 344-8
Mike Hoit's iilustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
ARTICLE
Flexib (Type
348
INTRODUCTION TO ARTICLE 348~-FLEXIBLE METAL CONDUIT (TYPE FMC) Flexible metal conduit (FMC), commonly called "Greenfieid" or "flex," is a raceway of an interlocked metal strip of either steel or aluminum. It's primarily used for the final 6 ft or less of raceways between a more rigid raceway system and equipment that moves, shakes, or vibrates. Examples of such equipment include pump motors and industrial machinery.
PART I. GENERAL
348.20 Trade Size.
348.1 Scope.
(A) Minimum. Flexible metal conduit smaller than trade size ¥2
Article 348 covers the use, instaliation, and con-
struction specifications for flexible metal conduit and associated fit-
must not be used, except trade size V?. can be used for the following
tings.
applications: (1) For enclosing the leads of motors.
348.2 Definition.
(2) Not exceeding 6 ft in length: Figure 348-1 Flexible Metal Conduit (Type FMC). A raceway of circular cross section made of a helically wound, formed, interlocked metal strip.
348.6 Listing Requirements.
Flexible metal conduit and
F M C - Size 348.20(A)(2)
associated fittings must be listed.
PART II. INSTALLATION 348.10 Uses Permitted.
Flexible metal conduit is permitted
exposed or concealed.
348.12 Uses Not Permitted. (1) In wet locations. (2) In hoistways, other than as permitted in 620.21 (A)(1).
Trade size 3/8 can be used in lengths not exceeding 6 ft for utilization equipment or tap connections to luminaires. Capyrtgnt 2011. www MilieHoltcoiK
(3) In storage battery rooms. (4) In any hazardous location, except as permitted by 501.10(6).
Figure 348-1
(5) Exposed to material having a deteriorating effect on the installed conductors.
a. For utilization equipment,
(6) Underground or embedded in poured concrete.
b. As part of a listed assembiy, or
(7) If subject to physical damage.
c. For luminaire tap connections, in accordance with 410.117(C).
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373
348.22
Flexible Metal Conduit (Type FMC)
348.24 Bends.
(3) In manufactured wiring systems, 604.6(A).
Bends must be made so that the conduit won't
be damaged, and its interna! diameter won't be effectively reduced.
(4) In hoistways, 620.21 (A)(1).
The radius of the curve of the inner edge of any field bend must not (5) As part of a listed luminaire assembiy in accordance with 410.137(C).
be less than shown in Table 2, Chapter 9 using the column "Other Bends."
(B) Máximum. Flexible metal conduit larger than trade size 4 must not be used.
348.26 Number of Bends (360°).
To reduce the stress
and friction on conductor insulation, the máximum number of bends (inciuding offsets) between pulí points must not exceed 360°.
348.22 Number of Conductors. Trade Size Vz and Larger
Flexible metal conduit must be large
enough to permit the instaliation and removal of conductors without
Author's Comment: There's no máximum distance between pulí boxes because this is a design issue, not a safety issue.
damaging the conductors' insulation. When all conductors in a raceway are the same size and insulation, the number of conductors permitted can be found in Annex C for the raceway type.
348.28 Trimming.
The cut ends of flexible metal conduit must
be trimmed to remove the rough edges, but this isn't necessary if fittings are threaded into the convolutions.
Question: How many 6 THHN conductors can be installed in trade size 1 flexible metal conduit?
348.30 Securing and Supporting. (A) Secureiy Fastened. Flexible metal conduit must be secureiy fas-
(a)2
(b)4
(c)6
(d)8
Answer: (c) 6 conductors [Annex C, Table C3]
tened by a means approved by the authority having jurisdiction within 1 ft of termination, and it must be secured and supported at intervals not exceeding 4V2 ft. Figure 348-2
Author's Comment: See 300.17 for additional examples on F M C - Secureiy Fastened 348.30(A)
how to size raceways when conductors aren't all the same size. Trade Size Va. The number and size of conductors in trade size ¥& flexible metal conduit must comply with Table 348.22.
Question: How many 12 THHN conductors can be installed in trade size 3€ flexible metal conduit that uses outside fittings? (ají
(b)3
(05
(d)7
Answer: (b) 3 conductors [Table 348.22] F M C must be secureiy fastened within 1 ft ! of termination a n d secured and supported ! at intervals not exceeding 41a ft.
One insulated, covered, or bare equipment grounding conductor of the same size is permitted with the circuit conductors. See the "*" note at Figure 348-2
the bottom of Table 348.22. Cables can be installed in flexible metal conduit as long as the number of cables doesn't exceed the allowable percentage fill speci-
Ex 1: Flexible metal conduit isn't required to be secureiy fastened or
fied in Table 1, Chapter 9.
supported
where fished behween access
points through concealed
spaces and supporting is Impracticable.
374
Mike HoiVs liiustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Rexible Metal Conduit (Type FMC)
348.60
F M C - Unsecured in Accessible Ceilings 348.30(A) Ex 4
FMC - Unsecured Where Flexibility is Necessary 348.30(A)
Ex 2
™
Where flexibility is necessary, the m á x i m u m unsecured length from the last point the FMC is secureiy fastened must not e x c e e d : • 3 f t f o r 1/2 through VU F M C
Last Point of [—Cable Support
•4ftfor1V2 and 2 F M C
• 5 ft for 2V2 F M C and larger
, Lengths not exceeding 6 ft can be unsecured within an accessible ceiling for luminaire(s) or other equipment.
Máximum of 1 ft From Tennination [348.30(A)]
Figure 348-4
F M C - Horizontal Support 348.30(B) F M C run horizontally through framing m e m b e r s is considered supported if secured within 1 ft of termination.
Figure 348-3
Max. 4V2ft
Metal Studs
Between Framing Members
f/; 5 n for trade sizes V2 tfirougfi VA (2) 4 ft for trade sizes VÁ ttirougti 2
Securing Required Within 1 ft of Termination
(3) 5 ft for trade sizes 21/2 and iarger Ex 4: FMC to a luminaire or electrical equipment within an
Wood Studs
accessible
ceiling ís permitted to be unsupported for not more than 6 ñ from the iastpoint where the raceway is secureiy fastened. Figure 348-4
Figure 348-5
(B) Horizontal Runs. Flexible metal conduit installed horizontally in bored or punched holes in wood or metal framing members, or
348.60 Grounding and Bonding.
notches in wooden members, is considered supported, but the race-
to minimize the transmission of vibration from equipment or to pro-
way must be secured within 1 ft of terminations. Figure 348-5
vide flexibility for equipment that requires movement after instalia-
if flexibility is necessary
tion, an equipment grounding conductor of the wire type must be
348.42 Fittings. Angle connectors
must not be concealed.
installed with the circuit conductors in accordance with 250.118(5), based on the rating of the circuit overcurrent device in accordance with 250.122. Figure 348-6
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375
Flexible Metal Conduit (Type FMC)
348.60
F M C - Equipment Grounding Conductor Flexibility Required After Instaliation 348.60
Equipment G r o u n d i n g Conductor - F M C 348.60
Where flexibility is necessary to minimize the transmission of vibration or to provide flexibility of equipment that requires movement after instaliation, an EGC of the wire type is required.
W h e r e flexibility isn't necessary after instaliation, a n d vibration isn't a c o n c e r n . F M C can serve a s t h e E G C w h e n : a. T h e conduit terminates in listed fittings b. T h e circuit is protected by a 2 0 A or less device c. 6 ft* c o m b i n e d length or less S e e 250.118(5)
CopyiígW 2011. mm.UikeHo»
com
Figure 348-6
*The total c o m b i n e d circuit length of flex u s e d a s a n e q u i p m e n t grounding conductor. C«pyrtBW2011,www.M*«H(*eom
If flexibility isn't necessary after instaliation, and vibration isn't a concern, the meta! armor of flexible metal conduit can sen/e as an equipment grounding conductor if the circuit conductors contained in the raceway are protected by an overcurrent device rated 20A or less,
Figure 348-7
and the combined length of the flexible metal raceway in the same ground-fault return path doesn't exceed 6 ft [250.118(5)]. Figure 348-7 If an equipment bonding jumper is installed outside of a raceway, the length of the equipment bonding jumper must not exceed 6 ft, and it must be routed with the raceway or enclosure in accordance with 250.102(E)(2).
376
Mike HoiVs iilustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
ARTICLE
350
Liquidtight Flexible Meta Conduit (Type LFMC)
INTRODUCTION TO ARTICLE 350—LIQUIDTIGHT FLEXIBLE METAL CONDUIT (TYPE LFMC) Liquidtight flexible metal conduit (LFMC), with its associated connectors and fittings, is a flexible raceway commonly used for connections ta equipment that víbrate or are required to move occasionally. Liquidtight flexible metal conduit is commonly called "Sealtight®" or "liquidtight" Liquidtight flexible metal conduit is of similar construction to flexible metal conduit, but it aiso has an outer liquidtight thermoplastic covering. It has the same primary purpose as flexible metal conduit, but it aiso provides protection from moisture and some corrosive effects.
PART I. GENERAL 350.1 Scope.
Liquidtight Flexible Metal Conduit (Type LFMC) 350.2 Definition
Article 350 covers the use, instaliation, and con-
struction specifications of liquidtight flexible metal conduit and associated fittings. Listed f LFMC ^ Fittings
350.2 Definition. Liquidtight Flexible Metal Conduit (Type LFMC). A raceway of circular cross section, having an outer liquidtight, nonmetallic, sunlightresistant jacket over an inner flexible metal core, with associated connectors and fittings for the instaliation of electric conductors. Rgure 350-1
350.6 Listing Requirements. Liquidtight
A circular raceway having an outer liquidtight, nonmetallic, sunlight-resistant jacket over a n inner flexible metal core. Copyright 2011. www.P*keHo1Lcom
flexible metal con-
duit and its associated fittings must be listed.
PART II. INSTALLATION
Figure 350-1
350.12 Uses Not Permitted. (1) If subject to physical damage.
350.10 Uses Permitted. (2) If the combination of the ambient and conductor operating tem(A) Permitted Use. Listed liquidtight flexible metal conduit is permit-
peratures exceeds the rating of the raceway.
ted, either exposed or concealed, at any of the following locations: (1) If flexibility or protection from liquids, vapors, or solids is required. (2) In hazardous locations, as permitted in 501.10(B), 502.10(A)(2), 502.10(B)(2),or 503.10(A)(2). (3) For direct burial, if listed and marked for this purpose.
350.20 Trade Size. (A) Minimum. Liquidtight flexible metal conduit smaller than trade size Vi must not be used. Ex: Liquidtight flexible metal conduit can be smaller than trade size Y? if installed in accordance with 348.20(A).
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350.22
Liquidtight Flexible Metal Conduit (Type LFMC)
Author's Comment: According to 348.20(A), LFMC smaller
Author's Comment: See 300.17 for additional examples on
than trade size Yi is permitted for tfie following:
how to size raceways when conductors aren't all the same size.
(1) For enclosing the leads of motors. (2) Not exceeding 6 ftin length: a. For utilization equipment,
Cables can be installed in liquidtight flexible metal conduit as long as the number of cables doesn't exceed the allowable percentage fill specified in Table 1, Chapter 9.
b. As part of a listed assembiy, or c. For tap connections to luminaires as permitted by 410.117(0).
(B) Raceway Trade Size Vb. The number and size of conductors in a
(3) In manufactured wiring systems, 604.6(A).
trade size Vs liquidtight flexible metal conduit must comply with Table
(4) In hoistways, 620.21 (A)(1).
348.22.
(5) As part of a listed assembiy to connect wired luminaire sections, 410.137(0. Question: How many 12 THHN conductors can be installed in (B) Máximum. Liquidtight flexible metal conduit larger than trade size
trade size 3€ LFMC that uses outside fittings?
4 must not be used. (a)1
350.22 Number of Conductors.
ib) 3
(0 5
(d)7
Answer: (b) 3 conductors [Table 348.22]
(A) Raceway Trade Size Vz and Larger. Raceways must be large enough to permit the instaliation and removal of conductors without damaging the insulation. When all conductors in a raceway are the same size and insulation, the number of conductors permitted can be found in Annex C for the raceway type.
One insulated, covered, or bare equipment grounding conductor ofthe same size is permitted with the circuit conductors. See the "*" noteat the bottom of Table 348.22.
350.24 Bends. Question: How many 6 THHN conductors can be installed in trade size 1 LFMC? Figure 350-2
Bends must be made so that the conduit won't be
damaged and the internal diameter of the conduit won't be effectively reduced. The radius of the curve of the inner edge of any field bend must not be less than shown in Table 2, Chapter 9 using the column
(a) 3
(b)5
(c)7
(d)9
Answer: (c) 7 conductors [Annex C, Table C. 7]
"Other Bends."
350.26 Number of Bends (360"*).
To reduce the stress
and friction on conductor insulation, the máximum number of bends (inciuding offsets) between pulí points must not exceed 360°. Author's Comment: There's no máximum distance between pulí boxes because this is a design issue, not a safety issue.
350.30 Securing and Supporting.
Liquidtight flexible metal
conduit must be secureiy fastened in place and supported in accordance with (A) and (B). (A) Secureiy Fastened. Liquidtight flexible metal conduit must be secureiy fastened by a means approved by the authority having jurisdiction within 1 ft of termination, and must be secured and supported
1 LFMC [Table C.7].
at intervals not exceeding 41/2 ft. Figure 350-3
W h e n all conductors in a raceway are the s a m e size and insulation, the number of conductors permitted can be found in A n n e x C. Figure 350-2
378
Ex 1: Liquidtight flexible metal conduit isn't required to be secureiy fastened or supported where fished behfi/een access points through concealed spaces and supporting is impracticable.
Mike HoiVs liiustrated Guide to Understanding the 2011 National Electncal Code, Volume 1
Liquidtight Flexible Metal Conduit (Type LFMC)
350.60
L F M C - Secureiy F a s t e n e d 350.30(A)
Ex 4: Lengths not exceeding 6 ft from the last point where the raceway is secureiy fastened can be unsecured within an accessible
ceil-
ing for luminaire(s) or other equipment. (B) Horizontal Runs. Liquidtight flexible metal conduit installed hor1 ftof Termination
izontally in bored or punched holes in wood or metal framing members, or notches in wooden members, is considered supported, but
Máximum -of4V2 fl
the raceway must be secured within 1 ft of termination. DO
t
350.42 Fittings. Angle
LFMC must be secureiy fastened within 1 ft of termination and at intervals not exceeding 4V2 ft.
Figure 350-3
I
connectors must not be concealed.
350.60 Grounding and Bonding.
If flexibility ¡s necessary
to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after instaliation, an equipment grounding conductor of the wire type must be installed with the circuit conductors in accordance with 250.118(6), based on the rating of the circuit overcurrent device in accordance
Ex 2: If flexibility is necessary
after instaliation, unsecured
lengths
with 250.122. Figure 350-5
from the last point where the raceway is secureiy fastened must not exceed: Figure 350-4 (1) 3 ñ for trade sizes Vz through VA (2) 4 ft for trade sizes VÁ through 2
L F M C - Equipment G r o u n d i n g Conductor Flexibility Required After Instaliation 350.60 II
(3) 5 ft for trade sizes 2Á and larger
Where flexibility is necessary to minimize the transmission of vibration or to provide flexibility of equipment that requires movement after instaliation. an EGC of the wire type is required.
LFMC - Unsecured Where Flexibility is Necessary 350.30(A)Ex2 W h e r e flexibility is necessary, the m á x i m u m unsecured length from t h e last point the L F M C is secureiy fastened must not e x c e e d : • 3 f t f o r V2 through 11/4 L F M C •4ftfor1V2and2LFMC • 5 ft for 2V2 L F M C and larger
Copynghl 2011. www MiksHolt com
Figure 350-5 M á x i m u m of 1 ft From Tennination [350.30(A)] If flexibility isn't necessary after instaliation, and vibration isn't a V/a L F M C , M á x i m u m Unsecured Length is 3 ft
concern, the metal armor of flexible metal conduit can serve as an equipment grounding conductor if the circuit conductors contained in the raceway are protected by an overcurrent device rated 20A or less, and the combined length of the flexible metal raceway in the same
Copyngnt 2011. www.MUieHMt com
Figure 350-4
ground-fault return path doesn't exceed 6 ft [250.118(6)]. If an equipment bonding jumper is installed outside of a raceway, the length of the equipment bonding jumper must not exceed 6 ft, and it must be routed with the raceway or enclosure in accordance with 250.102(E)(2).
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\ ARTICLE
352
Rigid Polyvinyl Chioride Conduit (TYPE PVC)
INTRODUCTION TO ARTICLE 352—RIGIO POLYVINYL CHLORIDE CONDUIT (TYPE PVC) Rigid polyvinyl chioride conduit (PVC) is a rigid nonmetallic conduit that provides many of the advantages of rigid metal conduit, while allowing instaliation in áreas that are wet or corrosive. It's an inexpensive raceway, and easily installed. It's lightweight, easily cut, glued together, and relatively strong. However, conduits manufactured from polyvinyl chioride (PVC) are brittle when coId, and they sag when hot. This type of conduit is commonly used as an underground raceway because of its low cost, ease of instaliation, and resistance to corrosión and decay.
PART I. GENERAL
PART II. INSTALLATION
352.1 Scope.
352.10 Uses Permitted.
Article 352 covers the use, instaliation, and con-
struction specifications of PVC conduit and associated fittings. Note: In extreme coId, PVC conduit can become brittle, and is more susceptible to physical damage.
352.2 Definition. Rigió Polyvinyl Chioride Conduit (PVC). A rigid nonmetallic conduit of
(A) Concealed. PVC conduit can be concealed within walls, floors, or
circular cross section with integral or associated couplings, listed for
ceilings, directly buried or embedded in concrete in buildings of any
the instaliation of electrical conductors and cables. Figure 352-1
height. (B) Corrosive Influences. PVC conduit is permitted in áreas subject to severe corrosión for which the material is specifically approved by
Rigid Polyvinyl Chioride Conduit - Type P V C 352.2 Definition
the authority having jurisdiction. Author's Comment: If subject to exposure to chemical solvents, vapors, spiashing, or immersion, materiais or coatings must either be inherently resistant to chemicals based upon their listing, or be identified for the specific chemical reagent [300.6(0(2)].
Schedule 4 0 P V C with Integral Coupling Copyngni ^ 1 V www klkMott c o n
(D) Wet Locations. PVC conduit is permitted in wet locations such as dairies, laundries, canneries, car washes, and other áreas frequently P V C Fittings
washed or in outdoor locations. Support fittings such as straps, screws, and bolts must be made of corrosion-resistant materiais, or
A rigid nonmetallic conduit with a circular cross section with integral or associated couplings. Figure 352-1
must be protected with a corrosion-resistant coating, in accordance with 300.6(A). (E) Dry and Damp Locations. PVC conduit is permitted in dry and damp locations, except where limited in 352.12.
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Rjgjd Polyvinyl Chioride Conduit (TYPE PVC)
Exposed. Schedule 40 PVC conduit is permitted for exposed locawhere not subject to physical damage. Figure 352-2
352.12
(G) Underground. PVC conduit installed underground must comply with the burial requirements of 300.5. (H) Support of Conduit Bodies. PVC conduit is permitted to support nonmetallic conduit bodies that aren't larger than the largest trade
P V C in Exposed Locations 352.10(F)
size of an entering raceway. These conduit bodies can't support luminaires or other equipment, and aren't permitted to contain devices, other than spiicing devices permitted by 110.14(B) and 314.16(C)(2). (I) Insulation Temperature Limitations. Conductors rated at a tem-
Schedule 4 0 P V C conduit is permitted w h e r e not subject physical d a m a g e .
perature higher than the listed temperature rating of PVC conduit must not be operated at a temperature above the raceway's listed temperature rating. Figure 3 5 2 - 4
P V C - Insulation Temperature Limitations
352.im
Copyngri12011 HWW.MikaHMlcorn
Figure 352-2 PVC
SCH40
Max 900C Wire
Sunlight Resistant
Ií PVC conduit is exposed to physical damage, the raceway must be identified for the application. Conductors rated at a temperature higher than the listed temperature rating of P V C conduit must not be operated at a temperature above the raceway's listed temperature rating.
Note: PVC Schedule 80 conduit is identified for use in áreas subject to physical damage. Figure 352-3
Copyngtil 3011, www M^eHoH com
P V C in Exposed Locations 352.10(F) Note
Figure 3 5 2 - 4
352.12 Uses Not Permitted. (A) Hazardous Locations. PVC conduit isn't permitted to be used in hazardous
locations except as permitted by 501.10(A)(1)(a) Ex,
503.10(A), 504.20, 514.8 Ex 2, and 515.8. (2) In Class I, División 2 locations, except as permitted in 501.10(B) (7). Schedule 8 0 P V C is identified for use in áreas subject to physical d a m a g e .
Figure 352-3
(B) Support of Luminaires. PVC conduit must not be used for the support of luminaires or other equipment not described in 352.1 OtH). Author's Comment: PVC conduit is permitted to support conduit bodies in accordance with 314.23(E) Ex.
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Rígíd Polyvinyl Chioride Conduit (TYPE PVC)
352.20
(0) Physical Damage. Schedule 40 PVC conduit must not be installed
Cables can be installed in PVC conduit, as long as the number of
if subject to physical damage, unless identified for the application.
cables doesn't exceed the allowable percentage fill specified in Table 1, Chapter 9.
Author's Comment: PVC Schedule 80 conduit is identified for use in áreas subject to physical damage [352.10(F) Note].
352.24 Bends.
Raceway bends must not be made in any manner
that would damage the raceway, or significantly change its intemal (D) Ambient Temperature. PVC conduit must not be installed if the ambient temperature exceeds 50°C (122°F).
diameter (no kinks). The radius of the curve of the inner edge of any field bend must not be less than shown in Table 2, Chapter 9.
352.20 Trade Size.
Author's Comment: Be sure to use equipment designed for
(A) Minimum. PVC conduit smaller than trade size
must not be
heating the nonmetallic raceway so it's pliable for bending (for example, a "hot box"). Don't use open-flame torches.
used. (B) Máximum. PVC conduit larger than trade size 6 must not be used.
352.22 Number of Conductors.
Raceways must be large
enough to permit the instaliation and removal of conductors without damaging the conductors' insulation, and the number of conduc-
352.26 Number of Bends (360°).
To reduce the stress
and friction on conductor insulation, the máximum number of bends (inciuding offsets) between pulí points must not exceed 360°. Figure 352-5
tors must not exceed that permitted by the percentage fill specified in Table 1, Chapter 9.
P V C - N u m b e r of B e n d s 352.26
When all conductors in a raceway are the same size and insulation, the number of conductors permitted can be found in Annex C for the raceway type.
90°
Question: How many 4/0 THHN conductors can be installed in trade size 2 Sctiedule 40 PVC? (a)2(b)4
(c)6
15°
90°
To reduce t h e stress a n d friction o n conductor insulation, the total a m o u n t of bends (inciuding offsets) between pulí points can't exceed 3 6 0 ° . .^go 15°
((98
Answer: (b) 4 conductors [Annex C, Table CIO] Copyiighl 2011. ww*.MIkcHoll com
Author's Comment: Schedule 80 PVC conduit has the same outside diameter as Schedule 40 PVC conduit, but the wall thickness of Schedule 80 PVC conduit is greater, which results
T h e r e ' s n o m á x i m u m distance b e t w e e n pulí points. Figure 352-5
in a reduced interior área for conductor fill.
352.28 Trimming. Question: How many 4/0 THHN conductors can be installed in
The cut ends of PVC conduit must be trimmed
(inside and out) to remove the burrs and rough edges.
trade size 2 Schedule 80 PVC conduit?
Author's comment: Trimming PVC conduit is very easy; most
(a)3
of the burrs will rub off with fingers, and a knife will smooth the
(b)5
(c)7
(d)9
rough edges. Answer: (a) 3 conductors [Annex C, Table C9]
352.30 Securing and Supporting. Author's Comment: See 300.17 for additional examples on
PVC conduit must be
secureiy fastened and supported in accordance with (A) and (B).
how to size raceways when conductors aren't all the same size.
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352.44
Rigid Polyvinyl Cliloride Conduit (TYPE PVC)
|A) Secured. PVC conduit must be secured within 3 ft of every box, cabinet, or termination fitting, such as a conduit body. Figure 352-6
Straight Run B e t w e e n Two Secureiy M o u n t e d Elbows
P V C - Expansión Fitting 352.44
Expansión Fitting P V C - Securing a n d Supporting 352.30
Expansión fitting(s) must be provided w h e r e t h e c h a n g e in length of a straight run between secureiy m o u n t e d Items is determined to be 1/4 in. or greater. Figure 352-7
Author's Comment: Table 352.44 in the NEC was created based on the following formula: Figure 352-8 Figure 352-6
Expansion/Contraction Inches = Raceway Length/100 x [(Temp Change/100) x 4.00]
(B) Supports. PVC conduit must be supported at intervals not exceeding the valúes in Table 352.30, and the raceway must be fastened in a manner that permits movement from thermai expansión or contraction. See Figure 352-6.
P V C - E x p a n s i ó n Fittings Table 352.44
I
Table 352.30 Trade Size
Support Spacing
^2-1
3ft
VA-2
5ft
Temperature Expansion/Contraction B a s e d o n 100°F C h a n g e
6fí 3^-5
7ft
6
8ft
PVC conduit installed horizontally in bored or punched holes in wood or metal framing members, or notches in wooden members, is considered supported, but the raceway must be secured within 3 ft of
10 2 0 3 0 4 0 5 0 NUMBER OF FEET
60
70
80
copy.^h,2oii
9 0 100 ^ m , . ^ i c ^
E x p n - C o n t In. = (Length/100) x (Temp C h a n g e / 1 0 0 x 4.0)
tennination. Figure 352-8
352.44 Expansión Fittings.
If PVC conduit is installed in a
straight run between secureiy mounted items, such as boxes, cabinets, elbows, or other conduit terminations, expansión fittings must be provided to compénsate for thermai expansión and contraction of tíie raceway in accordance with Table 352.44, if the length change is determined to be VA in. or greater. Figure 352-7
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352.46
Rigid Polyvinyl Chioride Conduit (TYPE PVC)
Example: How much will a 25 fí run of PVC conduit contract
352.48 Joints. Joints, such as couplings and connectors, must
when it's located in an ambient temperature change of25°F?
be made in a manner approved by the authority having jurisdiction.
(a)1 in.
(b)2in.
(c) 3 in
(d) 4 in.
Author's Comment: Follow the manufacturer's instructions for the raceway, fittings, and glue. Some glue requires the raceway
Answer: (a) 1 in. Expansion/Contraction Inches = Raceway Length/100 x ((Temp °F Change/100) x 4.00)
surface to be cleaned with a solvent before the application of the glue. After appiying glue to both surfaces, a quarter turn of the fitting is required.
Expansion/Contraction Inches = (25/100) x ((25/100) x 4.00) Expansion/Contraction Inches = 0.25 in.
352.60 Equipment Grounding Conductor, if equipment grounding is required, a sepárate equipment grounding conductor of
352.46 Bushings. Where a conduit enters a box, fitting, or other enclosure, the wire must be protected from abrasión.
the wire type must be installed within the conduit [300.2(B)]. Figure 352-10
Note: Conductors 4 AWG and larger that enter an enclosure must be protected from abrasión, during and after instaliation, by a fitting that provides a smooth, rounded insulating surface, such as an insulating bushing, unless the design of the box, fitting, or enclosure provides equivalent protection, in accordance with 300.4(G). Figure 352-9
P V C Grounding Equipment Grounding Conductors 352.60
W h e r e a n equipment grounding conductor is required, a sepárate equipment grounding conductor of the wire type must be installed within the conduit.
P V C - Bushings 352.46 and Note
Figure 352-10
Conductors 4 A W G and larger require a fitting that provides a smooth, rounded, insulating surface to protect the wire during and after instaliation. See 300.4(G).
Ex 2:An equipment grounding conductor isn't required in PVC conduit if the neutral conductor is used to ground sen/ice equipment, as permitted in 250.142(A) [250.24(C)]. Figure 352-11
Figure 352-9
Author's Comment: When PVC conduit is stubbed into an open-bottom switchboard, the raceway, inciuding the end fitting (bell-end), must not rise more than 3 in. above the bottom of the switchboard enclosure [300.16{B) and 408.5).
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Rigid Polyvinyl Chioride Conduit (TYPE PVC)
352.60
P V C - Grounding 352.60 Ex 2
An equipment grounding conductor isn't required in PVC if the service neutral conductor is connected to tfie service equipment via the main bonding jumper. Rgure 352-11
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• "
ARTICLE
35tJ
Liquidtight Flexible Nonmetallic Conduit (Type LFNC)
INTRODUCTION TO ARTICLE 356—LIQUIDTIGHT FLEXIBLE NONMETALLIC CONDUIT (TYPE LFNC) Liquidtight flexible nonmetallic conduit (LFNC) is a listed raceway of circular cross section having an outer liquidtight, nonmetallic, sunlightresistant jacket over an inner flexible core with associated couplings, connectors, and fittings.
PART I. GENERAL 356.1 Scope.
(1) Type LFNC-A (orange color). A smooth seamiess inner core and cover having reinforcement layers between the core and cover.
Article 356 covers the use, instaliation, and con-
struction specifications of liquidtight flexible nonmetallic conduit and
(2) Type LFNC-B (gray color). A smooth inner surface with integral
associated fittings.
reinforcement within the conduit wall. (3) Type LFNC-C (black color). A corrugated internal and extemal
356.2 Definition.
surface without integral reinforcement.
Liquidtight Flexible Nonmetallic Conduit (Type LFNC). A listed raceway of circular cross section, having an outer liquidtight, nonmetal-
356.6 Listing Requirement.
lic, sunlight-resistant jacket over a flexible inner core, with associated
conduit, and its associated fittings, must be listed.
Liquidtight flexible nonmetallic
couplings, connectors, and fittings, listed for the instaliation of electrical conductors. Figure 356-1
PART II. INSTALLATION Liquidtight Flexible Nonmetallic Conduit (Type L F N C ) 356.2 Definition
356.10 Uses Permitted.
usted liquidtight flexible nonmetal-
lic conduit is permitted, either exposed or concealed, at any of the following locations: (1) If flexibility is required. (2) If protection from liquids, vapors, or solids is required. (3) Outdoors, if listed and marked for this purpose. (4) Directly buried in the earth, if listed and marked for this purpose.
A circular raceway having a n outer liquidtight, sunlight-resistant jacket over a flexible inner core.
(5) LFNC-B {gray color) is permitted in lengths over 6 ft if secured according to 356.30. (6) LFNC-B (black color) as a listed manufactured prewired assembiy. (7) Encasement in concrete if listed for direct burial.
Figure 356-1
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Liquidtight Flexible Nonmetallic Conduit (Type LFNC)
356.12 Uses Not Permitted.
356.30
Question: How many 8 THHN conductors can be installed in
1) If subject to physicai damage.
trade size ^
LFNC-B?
í2i If the combination of ambient and conductor temperature will pro-
Answer: Six conductors [Annex C, Table C5]
duce an operating temperature above the rating of the raceway. (31 Longer than 6 ft, except if approved by the authority having jurisdiction as essential for a required degree of flexibility.
Author's Comment: See 300.17 for additional examples on how to size raceways when conductors aren't all the same size.
(4} If the operating voltage of the contained conductors exceeds 600 Cables can be installed in liquidtight flexible nonmetallic conduit, as
volts, nominal.
long as the number of cables doesn't exceed the allowable percent(5} In any hazardous
location, except as permitted by 501.10(B),
age fill specified in Table 1, Chapter 9.
502.10(A) and (B),and 504.20.
356.24 Bends.
356.20 Trade Size.
Raceway bends must not be made in any manner
that would damage the raceway or significantly change its internal
(A) Minimum. Liquidtight flexible nonmetallic conduit smaller than
diameter (no kinks). The radius of the curve of the inner edge of any
trade size Vi isn't permitted, except as permitted in the following:
field bend musí not be less than shown in Table 2, Chapter 9 using the column "Other Bends."
ili Enclosing the leads of motors, 430.245(B). (2) For tap connections
to lighting
fixtures
as permitted by
410.117(0).
356.26 Number of Bends (360'').
To reduce the stress
and friction on conductor insulation, the máximum number of bends
(B) Máximum. Liquidtight flexible nonmetallic conduit larger than trade size 4 isn't permitted.
(inciuding offsets) between pulí points must not exceed 360°. Author's Comment: There's no máximum distance between
356.22 Number of Conductors.
pulí boxes because this is a design issue, not a safety issue. Raceways must be large
enough to permit the instaliation and removal of conductors without damaging the insulation. When all conductors in a raceway are the
356.30 Securing and Supporting,
same size and insulation, the number of conductors permitted can be
must be secureiy fastened and supported in accordance with one of
found in Annex C for the raceway type. Figure 356-2
the following: Figure 356-3
LFNC-B (gray color)
L F N C - Secureiy F a s t e n e d 356.3Q{A)
L F N C - N u m b e r of C o n d u c t o r s 356.22
1 ftof Termination Máximum of3ft • A m á x i m u m of six 8 T H H N conductors can b e installed in Va LFNC-B [Table C.5]. When all conductors in a raceway are the s a m e size and insulation, the n u m b e r of conductors permitted can be f o u n d in A n n e x C. Figure 356-2
L F N C m u s t be secureiy fastened within 1 ft of termination a n d at intervals not exceeding 3 f t .
Figure 356-3
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356.42
Liquidtight Flexible Nonmetallic Conduit (Type LFNC)
(1) The conduit must be secureiy fastened at intervals not exceeding 3 ft, and within 1 ft of termination when installed longer than 6 ft. (2) Securing or supporting isn't required if it's fished, installed in lengths not exceeding 3 ft at termináis if flexibility is required, or
356.60 Equipment Grounding Conductor,
if equipment
grounding is required, a sepárate equipment grounding conductor of the wire type must be installed within the conduit [300.2(B)]. Figure 356-^
installed in lengths not exceeding 6 ft for tap conductors to luminaires, as permitted in 410.117(0). (3) Horizontal runs of liquidtight flexible nonmetallic conduit installed
L F N C - Equipment Grounding Conductor W h e r e Flexibility is Required
horizontally in bored or punched holes in wood or metal framing members, or notches in wooden members, are considered supported, but the raceway must be secured within 1 ft of termination. (4) Securing or supporting of LFNC-B (gray color) isn't required if installed in lengths not exceeding 6 ft from the last point where the raceway is secureiy fastened for connections within an accessible ceiling to luminaire(s) or other equipment.
356.42 Fittings.
Oniy fittings listed for use with liquidtight flexi-
ble nonmetallic conduit can be used [300.15]. Angle connector fittings must not be used in concealed raceway installations. Straight liquidtight flexible nonmetallic conduit fittings are permitted for direct burial
Figure 356-4
or encasement in concrete. Author's Comment: Conductors 4 AWG and larger that enter an enclosure must be protected from abrasión, during and after instaliation, by a fitting that provides a smooth, rounded, insulating surface, such as an insulating bushing, unless the design
If an equipment bonding jumper is installed outside of a raceway, the length of the equipment bonding jumper must not exceed 6 ft, and it must be routed with the raceway or enclosure in accordance with 250.102(E)(2).
of the box, fitting, or enclosure provides equivalent protection, in accordance with 300.4(G).
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ARTICLE
35
Electrical Metallic Tubing (Type EMT)
INTRODUCTION TO ARTICLE 358—ELECTRICAL METALUC TUBING CTYPE EMT) Electrical metallic tubing (EMT) is a lightweight raceway that's relatively easy to bend, cut, and ream. Because it isn't threaded, all connectors and couplings are of the threadless type and provide quick, easy, and inexpensive instaliation when compared to other metallic conduit systems, which makes it very popular. Electrical metallic tubing is manufactured in both galvanized steel and aluminum; the steel type is the most common type used.
PART I. GENERAL
PART II. INSTALLATION
358.1 Scope.
358.10 Uses Permitted.
Article 358 covers the use, instaliation, and con-
struction specifications of electrical metallic tubing.
(A) Exposed and Concealed. Electrical metallic tubing is permitted exposed or concealed.
358.2 Definition. Eléctrica! Metallic Tubing (Type EMT), A metallic tubing of circular cross section used for the instaliation and physical protection of electrical conductors when joined together with fittings. Figure 358-1
(B) Corrosión Protection. Electrical metallic tubing, elbows, couplings, and fittings can be installed in concrete, in direct contact with the earth, or in áreas subject to severe corrosive influences if protected by corrosión protection and approved as suitable for the condition. Figure 358-2
Electrical Metallic Tubing (Type E M T ) 358.2 Definition EMT - Uses Permitted Installed in Concrete or Earth 358.10(B)
I A metallic circular tubing used for the instaliation and physical protection of electrical conductors.
Compression
I
...
i
' i
Galvanized EMT installed in concrete on grade or above generally doesn't require supplemental corrosión protection.
Set Screw
Galvanized EMT in a below grade slab, in H, soil, or emerging from concrete to soil may require supplemental corrosión protection. ;/
Threadless E M T Fittings Figure 358-1 Figure 358-2
358.6 Listing Requirement.
Eiectricai metallic tubing,
elbows, and associated fittings must be listed.
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Electrical Metallic Tubing (Type EMT)
358.12
/ \: Supplementary
coatings
E M T - Uses N o t Permitted
for corrosión
protection (aspfialted paint) haven't been
358.12(5)
investi-
gated by a product testing and listing agency and these coatings are known to cause cáncer in laboratory animáis.
VIOLATION E M T isn't permitted ; to support luminaires or other equipment.
(C) Wet Locations. Support fittings, sucfi as screws, straps, and so on, installed in a wet location must be made of corrosion-resistant material, or a corrosion-resistant coating must protect them in accordance with 300.6. Author's Comment: Fittings used in wet locations must be listed for the application (wet location) [314.15]. For more information, visit http://wwAw.etpfittings.com/.
358.12 Uses Not Permitted.
CopyngM 2011.
www MiKeHoil com
iiiit/iÉr^ÉiittfttiiiMi Figure 358-3
EMT
must not be used under the
following conditions:
358.22 Number of Conductors. (1) Where, during instaliation or afterward, it will be subject to severe physical damage.
Raceways must be large
enough to permit the instaliation and removal of conductors without damaging the conductor insulation. When all conductors in a raceway
(2) If protected from corrosión solely by enamel. (3) In cinder concrete or cinder fill where subject to permanent mois-
are the same size and insulation, the number of conductors permitted can be found in Annex 0 for the raceway type.
ture, unless encased in not less than 2 in. of concrete. (4) In any hazardous
location, except as permitted by 502.10,
Question: How many 12 THHN conductors can be installed in ^ trade size 1 FMT? Figure 358-4
503.10, and 504.20. (5) For the support of luminaires or other equipment (like boxes), except conduit bodies no larger than the largest trade size of the
(a) 26
(b)28
(0 30 (d)32
Answer: (a) 26 conductors [Annex C, Table C. 1]
tubing that can be supported by the raceway. Figure 358-3 (6) If practical, contact with dissimilar metáis must be avoided to prevent the deterioration of the metal because of galvanic action.
Author's Comment: See 300.17 for additional examples on how to size raceways when conductors aren't all the same size.
Ex: Aluminum fittings are permitted on steel electrical metallic tubing, and steel fittings are permitted on aluminum EMT.
Cables can be installed in electrical metallic tubing, as long as the number of cables doesn't exceed the allowable percentage fill speci-
358.20 Tíade Size.
fied in Table 1, Chapter 9.
(A) Minimum. Electrical metallic tubing smaller than trade size ^2
358.24 Bends.
isn't permitted. (B) Máximum. Electrical metallic tubing larger than trade size 4 isn't permitted.
Raceway bends must not be made in any manner
that would damage the raceway, or significantly change its internal diameter (no kinks). The radius of the curve of the inner edge of any field bend must not be less than shown in Chapter 9, Table 2 for oneshot and full shoe benders. Author's Comment: This typically isn't a probiem, because most benders are made to comply with this table.
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Electrical Metallic Tubing (Type EMT)
358.30
E M T - N u m b e r of Conductors 358.22
358.28 Reaming and Threading, (A) Reaming. Reaming to remove the burrs and rough edges is required when the raceway is cut. Author's Comment: It's considered an accepted practice to ream small raceways with a screwdriver or the backside of pliers. (B) Threading. Electrical metallic tubing must not be threaded.
A m á x i m u m of twenty six 12 T H H N conductors can be installed in 1 E M T [Table C.1]. When all conductors in a raceway are the s a m e size and insulation, the n u m b e r of conductors permitted can be found in A n n e x C. Rgure 3 5 8 ^
358.30 Securing and Supporting.
Eiectricai metaiiic tubing
must be installed as a complete system in accordance with 300.18 [300.10 and 300.12], and it must be secureiy fastened in place and supported in accordance with (A) and (B). (A) Secureiy Fastened. Electrical metallic tubing must generally be secureiy fastened within 3 ft of every box, cabinet, or termination fit-
358.26 Number of Bends (360°).
To reduce the stress
ting, and at intervals not exceeding 10 ft. Figure 358-6
and friction on conductor insulation, tfie máximum number of bends (induding offsets) between pulí points can't exceed 360°. Figure 358-5
E M T - Secureiy Fastened 358.30(A} E M T - Number o f Bends 358.26
3ft Termination
10 ft M á x i m u m B e t w e e n Supports
3ft Termination ^
r 90°
15°
g To reduce the stress and friction o n conductor insulation, the total a m o u n t of bends (inciuding offsets) between pulí points can't exceed 3 6 0 ° .
3ft
6ft
4ft
3ft—
16ft E M T must be secureiy f a s t e n e d within 3 ft of termination fittings a n d at intervals not e x c e e d i n g 10 ft.
15°
C o p y r l ; ^ 2011. M M MiMHol com
• O Copyngtn 2011.
www
Figure 358-6
There's no m á x i m u m distance between pulí points. Figure 358-5
Author's Comment: Fastening is required within 3 ft of termination, not within 3 ft of a coupling.
Author's Comment: There's no máximum distance between
Ex 1: When structural
members
pulí boxes because this is a design issue, not a safety issue.
secured within Sñofa
box or termination fitting, an unbroken race-
way can be secured within Sftofa
don't permit
the raceway to be
box or termination fitting. Figure
358-7
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391
358.42
Electrical l\/letallic Tubing (Type EMT)
E M T - Secureiy Fastened to Structural M e m b e r s 358.30(A) Ex 1
Author's Comment: Conductors 4 AWG and larger that enter an enclosure must be protected from abrasión, during and after
VIOLATION E M T must be unbroken between termination in this c a s e . *
^
>
»
instaliation, by a fitting that provides a smooth, rounded, insulating surface, such as an insulating bushing, unless the design of the box, fitting, or enclosure provides equivalent protection, in *
* -
*
"
— - ^ - " - ^
'^^^
•
^
* *
*
*
I
accordance with 300.4{G}. Figure 358-8
r-^
E M T - Bushings 300.4(G)
n
Máximum Máximum 5ft 5ft Where structural m e m b e r s don't pennlt fastening within 3 ft of the termination, E M T must be secured within 5 ft.
Fitting Termination
Copynghl 2011. « w » M*«Holl.com
Figure 35&-7
(B) Horizontal Runs. Electrical metallic tubing installed horizontally in bored or punched holes in wood or metal framing members, or
í
6 AWG a n d Smaller Bushing Not Required
4 AWG a n d Larger Bushing Required
notches in wooden members, is considered supported, but the raceway must be secured within 3 ft of termination. CopyriOM 2011. «ww.hMieHoli.com
358.42 Couplings and Connectors.
couplings and connec-
Figure 358-8
tors must be made up tight to maintain an effective ground-fault current path to safely conduct fault current in accordance with 250.4(A) (5), 250.96(A), and 300.10. If buried in masonry or concrete, threadless electrical metallic tubing fittings must be of the concrete-tight type. If installed in wet locations, fittings must be listed for use in wet locations in accordance with 314.15(A).
392
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
ARTICLE
362
Electrical Nonmetallic Tubing (Type ENT)
INTRODUCTION TO ARTICLE 362—ELECTRICAL NONMETALLIC TUBING (TYPE ENT) Electrical nonmetallic tubing (ENT) is a pliable, corrugated, circular raceway made of polyvinyl chioride. In some parts of the country, the field ñame for electrical nonmetallic tubing is "Smurf Pipe" or "Smurf Tube," because it was only available in blue when it originally came out at the time the children's cartoon characters "The Smurfs" were most popular. Today, the raceway is available in a rainbow of colors such as white, yellow, red, green, and orange, and is soid in both fixed lengths and on reels.
PART I. GENERAL
PART II. INSTALLATION
362.1 Scope.
362.10 Uses Permitted.
Article 362 covers the use, instaliation, and con-
struction specifications of electrical nonmetallic tubing and associated fittings.
Definition of First Floor. The first floor of a building is the floor with 50 percent or more of the exterior wall surface área level with or above finished grade. If one additional level not designed for human
362.2 Definition.
habitation and used only for vehicle parking, storage, or similar use
Electrical Nonmetallic Tubing (Type ENT). A pliable corrugated race-
is at ground level, then the first of the three permissible floors can be
way of circular cross section, with integral or associated couplings,
the next higher floor
connectors, and fittings listed for the instaliation of electrical conductors. Figure 362-1
(1) In buildings not exceeding three floors. Figure 362-2
Electrical nonmetallic tubing can be bent by hand with a reasonable forcé, but without other assistance.
E N T - Building Not Over 3 Floors 362.10(1)
Electrical Nonmetallic Tubing (Type E N T ) 362.2 Definition Listed E N T Fittings
j ^
In a building not over 3 floors, E N T c a n be run e x p o s e d , concealed, or above a s u s p e n d e d ceiling.
A pliable corrugated circular raceway with integral or associated couplings, connectors, and fittings listed for the instaliation of electrical conductors. Copynghl 2011, www.MitieHollcoin
Figure 362-1
CopyrigM 2011. w«w,M
Figure 362-2
mke Holt Enterprises, Inc. • www.MikeHolt.com • 888.NEC.C0DE (632.2633)
362.10
Electrical Nonmetallic Tubing (Type ENT)
E N T - Fire Sprinkied Building 362.10(2) Ex
a. Exposed, where not prohibited by 362.12. b. Concealed within walls, floors, and ceilings. (2) In buildings exceeding three floors, electrical nonmetallic tubing can be installed concealed in walls, floors, or ceilings that provide a thermai barrier having a 15-minute finish rating, as identified in listings of fire-rated assemblies. Figure 362-3
sprinkier System (all floors) uilding Over 3 Floors 362.10(2)
In buildings over 3 floors, E N T must be concealed behind floors, walls, or ceilings that have a 15-minute fínish rating. i
W h e n a ftre sprinkier s y s t e m is installed on all floors, E N T can be installed e x p o s e d or , c o n c e a l e d regardiess of the finish rating.
n
Figure 362-4
P^^^i IJLJiLi.__:
E N T - S u s p e n d e d Ceiling - Over 3 Floors 362.10(5)
Copynghl 2011, n w * MrtieMott.com
Figure 362-3
Ex to (2): If a fire sprinlder system is installed on all floors, in accordance with NFPA 13, Standard
for the Instaliation
of
Sprinkier
Systems, electrical nonmetallic tubing is permitted exposed or concealed in buildings ofany height. Figure 362-4
E N T is pemnitted above a s u s p e n d e d ceiling ^ 1 (not used for environmental air) if the suspended L ¿ i ™ l ceiling provides a 15-minute finish rating.
(3) Electrical nonmetallic tubing is permitted in severe corrosive and chemical locations, when identified for this use. (4) Electrical nonmetallic tubing is permitted in dry and damp concealed locations, if not prohibited by 362.12. (5) Electrical nonmetallic tubing is permitted above a suspended ceiling, if the suspended ceiling provides a thermai barrier having
Figure 362-5
a 15-minute finish rating, as identified in listings of fire-rated assemblies. Figure 362-5
(6) Electrical nonmetallic tubing can be encased or embedded in a
Ex: If a fire sprinkier system is installed on all floors, in accordance with NFPA 13, Standard for the Instaliation of Sprinkier Systems,
elec-
trical nonmetallic tubing is permitted above a suspended ceiling that doesn't have a 15-minute finish rated thermai barrier material. Figure
concrete slab provided fittings identified for the purpose are used. Author's Comment: Electrical nonmetallic tubing isn't permitted in the earth [362.12(5)].
362-6
Mike HoWs lllustrated Guide to Understanding the 2011 National Electncal Code, Volume 1
Electrical E
Nonmetallic Tubing (Type ENT)
362.12
ENT - Fire Sprinkied Buildings O v e r 3 Floors A b o v e S u s p e n d e d Ceiling 362.10(5) Ex
E N T - Operating Temperature 362.10(9)
Conductors or cables rated above the E N T temperature rating must not opérate a b o v e the raceway's listed temperature rating.
Suspended ' i Ceiling . i ^ V " »
Sprinkier S y s t e m (all floors)
Copynghl ?0t 1, www MMHolt com
Figure 3 6 2 - 7
W h e n a fire sprinkier system is installed o n all floors, E N T c a n b e installed a b o v e a s u s p e n d e d ceiling regardiess of the finish rating.
(6) Exposed in buildings over three floors, except as permitted by 362.10(2) and (5) Ex. (7) In assembiy occupancies or theaters, except as permitted by
Figure 362-6
518.4 and 520.5. (8) Exposed to the direct rays of the sun for an extended period,
(7) Electrical nonmetallic tubing is permitted in wet locations indoors,
unless listed as sunlight resistant.
or in a concrete slab on or below grade, with fittings listed for the Author's Comment: Exposing electrical nonmetallic tubing to
purpose.
the direct rays of the sun for an extended time may result in the (8) Listed prewired electrical nonmetallic tubing with conductors is permitted in trade sizes V2, % and 1.
product becoming brittle, unless it's listed to resist the effects of ultraviolet (UV) radiation. Figure 3 6 2 - 8
(9) Conductors rated at a temperature higher than the listed temperature rating of ENT must not be operated at a temperature above E N T - E x p o s e d t o Direct S u n 362.12(8)
the raceways listed temperature rating. Figure 362-7
362.12 Uses Not Permitted. (1) In any hazardous
location, except as permitted by 504.20 and
505.15(A)(1). (2) For the support of luminaires or equipment. See 314.2. (3) If the ambient temperature exceeds 50°C (122°F). (4) For direct earth burial. Author's Comment:
Electrical nonmetallic tubing can be
encased in concrete [362.10(6)]. (5) As a wiring method for systems over 600V. Figure 362-8
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395
362.20
Electrical Nonmetallic Tubing (Type ENT)
Author's Comment: There's no máximum distance between
(9) If subject to physical damage.
pulí boxes because this is a design issue, not a safety issue. Author's Comment: Electrical nonmetallic tubing is prohibited in ducts, cavity plenum spaces [300.22{C)], and patient care área circuits in health care facilities [517.13(A)].
362.28 Trimming.
The cut ends of electrical nonmetallic tubing
must be trimmed (inside and out) to remove the burrs and rough edges.
,. • .
362.20 Trade Sizes. Trimming electrical nonmetallic tubing is very easy; most of the burrs (A) Minimum. Electrical nonmetallic tubing smaller than trade size Vi
rub off with fingers, and a knife can be used to smooth the rough
isn't permitted.
edges.
(B) Máximum. Eléctrica! nonmetallic tubing larger than trade size 2 isn't permitted.
362.30 Securing and Supporting.
Eiectricai nonmetallic
tubing must be installed as a complete system in accordance with
362.22 Number of Conductors.
Raceways must be large
300.18 [300.10 and 300.12], and it must be secureiy fastened in
enough to permit the instaliation and removal of conductors with-
place and supported in accordance with (A) and (B).
out damaging the conductors' insulation, and the number of conduc-
(A) Secureiy Fastened. Electrical nonmetallic tubing must be secured
tors must not exceed that permitted by the percentage fill specified in
within 3 ft of every box, cabinet, or termination fitting, such as a con-
Table 1, Chapter 9.
duit body, and at intervals not exceeding 3 ft. Figure 362-9
When all conductors in a raceway are the same size and insulation, the number of conductors permitted can be found in Annex C for the
ENT - Secured and Supported
raceway type.
362.30(A) Question: How many 12 THHN conductors can be installed in trade size Á ENT? (a) 5
(b)7
(09
(d)11
Answer: (b) 7 conductors [Annex C, Table C2]
Author's Comment: See 300.17 for additional examples on how to size raceways when conductors aren't all the same size. Cables can be installed in electrical nonmetallic tubing, as long as the cables don't exceed the allowable percentage fill specified in Table 1,
ENT installed horizontally through framing members is considered secured and supported.
Chapter 9. Figure 362-9
362.24 Bends.
Raceway bends must not be made in any manner
that would damage the raceway, or significantly change its internal diameter (no kinks). The radius of the curve to the centerline of any
Ex 2: Lengths not exceeding 6 ñ from the last point if the raceway is
field bend must not be less than shown in Chapter 9, Table 2, using
secureiy fastened within an accessible
the column "Other Bends."
equipment
382.26 Number of Bends (360°).
To reduce the stress
and friction on conductor insulation, the máximum number of bends
ceiling to luminaire(s) or other
Ex 3: If fished between access points through concealed spaces anú supporting is impractical.
(inciuding offsets) between pulí points can't exceed 360°.
Mike HoiVs Iliustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Electrical Nonmetallic Tubing (Type ENT)
362.60
(B) Horizontal Runs. Electrical nonmetallic tubing installed horizon-
ENT - Equipment Grounding
tally in bored or punched holes in wood or metal framing members, or notches in wooden members, is considered supported, but the raceway must be secured within 3 ft of terminations.
362.46 Bushings.
Conductors 4 AWG and larger that enter an
enclosure from a fitting must be protected from abrasión, during and after instaliation, by a fitting that provides a smooth, rounded, insulating surface, such as an insulating bushing, unless the design of the box, fitting, or enclosure provides equivalent protection, in accordance www.Mik8Holt,com
with300.4{G).
362.48 Joints.
Joints, such as couplings and connectors, must
W h e r e e q u i p m e n t g r o u n d i n g is required, a sepárate e q u i p m e n t grounding conductor of t h e wire type must be installed in t h e raceway.
be made in a manner approved by the authority having jurisdiction. Figure 3 6 2 - 1 0 Author's Comment: Follow the manufacturer's instructions for the raceway, fittings, and glue, According to product listings, PVC conduit fittings are permitted with electrical nonmetallic tubing. / \: Glue used with electrical nonmetallic tubing must be listed for ENT. Glue for PVC conduit must not be used with electrical nonmetallic tubing because it damages the plástic from which ENTis manufactured.
362.60 Equipment Grounding Conductor,
if equipment
grounding is required, a sepárate equipment grounding conductor of the wire type must be installed within the raceway. Figure 3 6 2 - 1 0
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397
ARTICLE
376
Metal Wireways
INTRODUCTION TO ARTICLE 376—METAL WIREWAYS Metal wireways are commonly used wtiere access to the conductors within the raceway is required to make terminations, spiices, or taps to several devices at a single location. High cost precludes their use for other than short distances, except in some commercial or industrial occupancies where the wiring is frequently revised. Author's Comment: Both metal wireways and nonmetallic wireways are often called "troughs" or "gutters" in the field.
PART 1. GENERAL
PART II. INSTALLATION
376.1 Scope.
376.10 Uses Permitted.
Article 376 covers the use, instaliation, and con-
struction specifications of metal wireways and associated fittings.
376.2 Definition.
(1) Exposed. (2) In any hazardous locations, as permitted by other articles in the
Metal Wireway. A sheet metal trough with hinged or removable covers for housing and protecting electric conductors and cable, and in which conductors are placed after the wireway has been installed.
Cade. (3) Wet locations where listed for the purpose. (4) Unbroken through walls, partitions, and floors.
Figure 376-1 Author's Comment: See 501.10{B), 502.10(B), and 504.20 for metal wireways used in hazardous locations. Metal W i r e w a y 376.2 Definition
376.12 Uses Not Permitted. (1) Where subject to severe physical damage. (2) Where subject to corrosive environments.
376.21 Conductors—IVIaximum Size.
i h e máximum size
conductor permitted in a wireway must not be larger than that for which the wireway is designed.
A sheet metal trough with hinged or removable covers for housing and protecting electnc wires and cable, and in which conductors are placed after the wireway has been installed.
Figure 376-1
376.22 Number of Conductors and Ampacity. The number of conductors and their ampacity must comply with 376.22{A) and (B). (A) Number of Conductors. The máximum number of conductors permitted in a wireway is limited to 20 percent of the cross-sectional área ot the wireway. Figure 376-2
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Metal Wireways
376.56
Wireway - Number of Conductors
Signaling and motor control conductors between a motor and its starter used only for starting duty aren't considered current carrying
The máximum number of conductors permitted in a wireway is limited to 20 percent of the cross-sectional área of the wireway.
for conductor ampacity adjustment.
376.23 Wireway Sizing. (A) Sizing for Conductor Bending Radius. If conductors are bent
^.1
í,'—J
L^t
Site
within a metal wireway, the wireway must be sized to meet the bend-
.
B 9 p v
CBp|«igMM11
ing radius requirements contained in Table 312.6(A), based on one wire per terminal. Figure 376-4
W i r e w a y Sizing Conductor Bending Radius 376.23(A)
Rgure 376-2
Author's Comment: Spiices and taps must not fill more than 75 percent of the wiring space at any cross section [376.56]. (B) Conductor Ampacity Adjustment Factors. When more than 30 current-carrying conductors are installed in any cross-sectional área ofthe wireway, the conductor ampacity, as listed in Table 310.15(B) (16), must be adjusted in accordance with Table 310.15(B)(3)(a). Figure 376-3
W h e r e conductors are bent, the wireway must be sized t o meet the bending radius of Table 312.6{A), based o n o n e wire per terminal. Copynght20t1. wwwPiU
Figure 376-4 Wireway - Conductor A m p a c i t y 376.22(B) When more than 3 0 current-carrying conductors are installed in any cross-sectional área, conductor ampacity from Table 310.15(B){16) must be adjusted in accordance with 310.15(B)(3)(a).
376.30 Supports. Wireways
must be supported in accordance
with (A) and (B). (A) Horizontal Support. If installed honzontally, metal wireways must be supported at each end and at intervals not exceeding 5 ft. (B) Vertical Support. If installed vertically, metal wireways must be
SS* lof»
Man So(6
1
2
Mw leit
3
Uw> idt
Mw 5*8
HH. 6oíS
4
5
6
• É l
one joint between supports.
376.56 Spiices, Taps, and Power Distribution Biocics.
r ii
ímmmámm Figure 376-3
secureiy supported at intervals not exceeding 15 ft, with no more than
(A) Spiices and Taps. Spiices and taps in metal wireways must be accessible, and they must not fill the wireway to more than 75 percent of its cross-sectional área. Figure 376-5 Author's Comment: The máximum number of conductors permitted in a metal wireway is limited to 20 percent of its cross-sectional área at any point [376.22(A)].
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399
376.56
Metal Wireways
Spiices and taps must be accessible a n d not fill more than 7 5 % of the cross-sectional área of the wireway.
Power distribution biocks must not have uninsulated e x p o s e d live parts in the metal w i r e w a y after instaliation w h e t h e r or not the w i r e w a y cover is installed. Figure 376-6
Figure 376-5
(B) Power Distribution Biocks. (1) Instaliation. Power distribution biocks installed in wireways must be listed. (2) Size of Enclosure. In addition to the wiring space requirements [376.56(A)], the power distribution block must be installed in a metal wireway not smaller than specified in the instaliation instructions of the power distribution block. (3) Wire-Bending Space. Wire-bending space at the termináis of power distribution biocks must comply with 312.6(B). (4) Live Parts. Power distribution biocks must not have uninsulated exposed live parts in the metal wireway after instaliation, whether or not the wireway cover is installed. Figure 376-6
400
Mike HolVs lllustrated Guide to Understanding the 2011 National Eleotrical Code, Volume 1
ARTICLE
380
Multioutlet Assemblies
INTRODUCTION TO ARTICLE 380—MULTIOUTLET ASSEMBLIES A multioutlet assembiy is a surface, flush, or freestanding raceway designed to hold conductors and receptacles, and is assembled in the field or at the factory [Article 100]. It's not limited to systems commonly referred to by the trade ñames "Plugtrak®" or "Plugmoid®."
PARI L GENERAL
PART IL INSTALLATION
380.1 Scope.
380.10 Uses Permitted.
Article 380 covers the use, instaliation, and con-
struction specifications of multioutlet assemblies. Author's Comment: A multioutlet assembiy is a surface, flush
Multioutlet assemblies are only per-
mitted in dry locations.
380.12 Uses Not Permitted.
or freestanding raceway designed to hold conductors and receptacles assembled in the field or at the factory [Article 100]. Figure 380-1
(1) Concealed. (2) If subject to severe physical damage. (3) If the voltage is 300V or more between conductors, unless the metal has a thickness not less than 0.04 in.
Multioutlet A s s e m b i y Article 100 Defir)ition
(4) If subject to corrosive vapors. (5) In hoistways.
Freestanding Power Pole
(6) In any hazardous location, except as permitted by 501.10(B).
380.76 Througli Partitions.
Metal multioutlet assemblies can
pass through a dry partition provided no receptacle is concealed in the wall, and the cover of the exposed portion of the system can be removed.
A surface, flush, or freestanding raceway designed to hold conductors a n d receptacles assembled in t h e field or at the factory. Figure 380-1
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401
ARTICLE
Surface Metal Raceways INTRODUCTION TO ARTICLE 386—SURFACE METAL RACEWAYS A surface metal raceway is a common method of adding a raceway when exposed traditional raceway systems aren't acceptable, and concealing the raceway isn't economically feasible. It comes in several colors, and is now available with colored or real wood inserts designed to make it look like molding rather than a raceway. Surface metal raceway is commonly known as "Wiremoid®" in the field.
PART I. GENERAL 386.1 Scope.
Author's Comment: Surface metal raceways are available in different shapes and sizes and can be mounted on walls, ceil-
This article covers the use, instaliation, and con-
ings, or floors. Some surface metal raceways have two or more
struction specifications of surface metal raceways and associated fit-
sepárate compartments, which permit the separation of power
tings.
and lighting conductors from low-voltage or limited-energy conductors or cables (control, signal, and Communications cables
386.2 Definition.
and conductors) [386.70].
Surface Metal Raceway. A metallic raceway intended to be mounted to the surface, with associated accessories, in which conductors are
386.6 Listing Requirements.
placed after the raceway has been installed as a complete system
associated fittings must be listed.
Surface metal raceways and
[300.18(A)]. Figure 380-1 Author's Comment: Enclosures for switches, receptacles, luminaires, and other devices are identified by the markings on Surface Metal R a c e w a y s 386.2 Definition
their packaging, which identify the type of surface metal raceway that can be used with the enclosure.
PART II. INSTALLATION 386.10 Uses Permitted. (1) In dry locations. Figure 386-2 (2) In Class I, División 2 locations, as permitted in 501.10{B)(3). A raceway intended l o be m o u n t e d to the surface, in which conductors are placed after the raceway has been installed as a complete s y s t e m . Copyright 2011. www UkeHott.ccxn
(3) Under raised floors, as permitted in 645.5(E)(2). (4) Run through walls and floors, if access to the conductors is maintained on both sides of the wall, partition, or floor.
Figure 386-1
402
Mike HolVs lllustrated Guide to Understanding the 2011 National Electrk)al Code, Volume 1
Surface Metal Raceways
386.60
Surface Metal Raceway - Dry Locations 386.10(1)
The ampacity adjustment factors of 310.15(B)(3)(a) don't apply to conductors installed in surface metal raceways if all of the following conditions are met: Figure 386-3
Suspended Ceiling Surface R a c e w a y - Conductor Fill 386.22
Surface metal raceways are permitted to be installed ín dry locations.
T h e ampacity adjustment factors o f 310.15{B){3)(a) don't apply w h e r e all o f t h e following conditions are met: (1) T h e cross-sectional área exceeds 4 sq in., (2) T h e n u m b e r of current-carrying conductors doesn't exceed 30, a n d (3) T h e conductor fill doesn't exceed 2 0 % of the cross-sectional área of the raceway.
CopyiWH 2011. MM>.Wk9Holl com
Figure 386-2
Copyright 2011, www.WKeHcXi.i^
386.12 Uses Not Permitted.
Figure 386-3
(1) If subject to severe physical damage, unless othenwise approved by the authority having jurisdiction.
( 1 ) The cross-sectional área of the raceway exceeds 4 sq in.
(2) If the voltage is 300V or more behween conductors, unless the metal has a thickness not less than 0.04 in. (3} If subject to corrosive vapors.
and (3) The sum of the cross-sectional áreas of all contained conductors doesn't exceed 20 percent of the interior cross-sectional área of
(4) In hoistways. (5) If concealed, except as permitted in 386.10.
386.21 Size of Conductors.
(2) The number of current-carrying conductors doesn't exceed 30,
The máximum size conductor
permitted in a surface metal wireway must not be larger than that for which the wireway is designed. Author's Comment: Because partial packages are often purchased, you may not always receive this information.
the raceway.
386.30 Securing and Supporting.
Surface metal raceways
must be secured and supported at intervals in accordance with the manufacturer's instaliation instructions.
386.56 Spiices and Taps.
Spiices and taps must be acces-
sible, and must not fill the raceway to more than 75 percent of its cross-sectional área.
386.22 Number of Conductors. The number of conduc-
386.60 Equipment Grounding Conductor.
tors or cables installed in a surface metal raceway must not be more
raceway fittings must be mechanically and eiectrically joined together
than the number for which the raceway is designed. Cables can be
in a manner that doesn't subject the conductors to abrasión. Surface
installed in surface metal raceways as long as the number of cables
metal raceways that allow a transition to another wiring method, such
Surface metal
doesn't exceed the allowable percentage fill specified in Table 1,
as knockouts for connecting raceways, must have a means for the
Chapter 9.
termination of an equipment grounding conductor. A surface metal raceway is considered suitable as an equipment grounding conductor, in accordance with 250.118(14).
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386.70
Surface Metal Raceways
386,70 Sepárate Compartments.
If surface metal race-
ways have sepárate compartments within a single raceway, power and lighting conductors can occupy one compartment, and the other compartment may contain control, signaling, or Communications wiring. Stamping, imprinting, or color coding of the interior finish must identify the sepárate compartments, and the same relativo position of compartments must be maintained throughout the premises.
Author's Comments: • Separation from power conductors is required by the NEC ior the following low-voltage and limited-energy systems: -
CATV,820.44{F)(1)
-
Communications, 800.133(A)(1)
-
Control and Signaling, 725.136(6)
-
Fire Alarms, 760.136(B)
-
Intrinsically Safe Systems, 504.30(A)(2)
-
Instrumentation Tray Cable, 727.5
-
Radio and Televisión, 810.18(0)
-
Sound Systems, 640.9(C)
• Nonconductive optical fiber cables can occupy the same cable tray or raceway as conductors for electric light, power, Class 1, or nonpower-limited fire alarm circuits [770.133(A)].
404
Mike Holt's lllustrated Guide to Understanding the 2011 National Eléctrica! Code, Volume 1
ARTICLE
392
Cable Trays
INTRODUCTION TO ARTICLE 392—CABLE TRAYS A cable tray system is a unit or an assembiy of units or sections with associated fittings that forms a structural system used to secureiy fasten or support cables and raceways. Cable tray systems include ladder, ventilated trough, ventilated channel, solid bottom, and other similar structures. Cable trays are manufactured in many forms, from a simple hanger or wire mesh to a substantial, rigid, steel support system. Cable trays are designed and manufactured to support specific wiring methods, as identified in 392.10(A).
PART L GENERAL
PART IL INSTALLATION
392.1 Scope.
392.10 Uses Permitted.
Article 392 covers cable tray systems, inciuding
Cable trays can be used as a sup-
ladder, ventilated trough, ventilated channel, solid bottom, and other
port system for sen/ice, feeder, or branch-circuit conductors, as well
similar structures.
as Communications circuits, control circuits, and signaling circuits. Figure 392-2
392.2 Definition. Cable Tray System. A unit or assembiy of units or sections with associated fittings forming a rigid structural system used to secureiy fasten or support cables, raceways, and boxes. Figure 392-1
I I
I i
Cable Tray S y s t e m 392.2 Definition
Cable trays can b e u s e d a s a support s y s t e m for: • Service Conductors • Feeders • Branch Circuits Copynghl 2011,
A unit or assembiy of units or sections with associated fittings forming a rigid structural system used to secureiy fasten or support cables, raceways, and boxes. Figure 392-1
wwivM*eHoll com
Figure 392-2
Author's Comment: Cable trays used to support serviceentrance
Author's Comment: Cable tray isn't a type of raceway. It's a
• C o m m u n i c a t i o n s Circuits • Control Circuits • Signaling Circuits
conductors
must
contain
only
service-entrance
conductors unless a solid fixed barrier sepárales the serviceentrance conductors from other conductors [230.44].
support system for cables and raceways.
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405
392.12
Cable Trays
Author's Comments:
Author's Comment: Control, signal, and Communications
• Cable tray installations aren't limited to industrial establishments.
cables must be separated from the power conductors by a bar-
i
rier or maintain a 2 in. separation.
I
• Coaxial Cables, 820.133{A){1)(b) Ex 1
I
tors and jacketed cables must be identified as being sunlight
• Class 2 and 3 Cables, 725.136(6) and 725.136(1)
I
resistant. The manufacturer must identify cable trays and
• Communications Cables, 800.133(A)(2) Ex 1
I
associated fittings for their intended use.
• Fire Alarm Cables, 760.136(0)
I
• Optical Fiber Cables, 770,133(8)
I
• If exposed to the direct rays of the sun, insulated conduc-
(A) Wiring Methods. Any wiring methods listed in Table 392.10(A)
• Intrinsically Safe Systems Cables, 504.30(A)(2) Ex 1
I
can be installed in a cable tray.
• Radio and Televisión Cables, 810.18(B) Ex 1
I
Table 392.10(A) Wiring Methods Wiring Method
(B) In Industrial Establishments.
Article/Section
(1) Where conditions of maintenance and supervisión ensure that ' only qualified persons service the installed cable tray system,
Armored Cable
320
CATV cables
820
CATV raceways
820
Class 2 & 3 cables
725
Communications cables
800
(c) Equipment grounding conductors must be 4 AWG and larger
Communications raceways
800
(C) Hazardous Locations. Cable trays in hazardous locations must
Electrical metallic tubing
358
contain only the cable types and raceways permitted by the M e for
Electrical nonmetallic tubing
362
the application
Fire alarm cables
760
Flexible metal conduit
348
Instrumentation tray cable
727
Intermedíate metal conduit
342
(D) Nonmetallic Cable Trays. In addition to the uses permitted else-
Liquidtight flexible metal conduit
350
where in Article 392, nonmetallic cable trays can be installed in corro-
Liquidtight flexible nonmetallic conduit
356
Metal-ciad cable
330
392.12 Uses Not Permitted.
Nonmetallic-Sheathed cable
334
mitted in hoistways, or where subject to severe physical damage,
Nonpower-limited fire alarm cable
760
Optical fiber cables and raceways
770
392.18 Cable Tray installations
Polyvinyl chioride PVC conduit
352
(A) Complete System. Cable trays must be installed as a complete
Power and control tray cable
336
system, except mechanically discontinuóos segments between cable
Power-limited fire alarm cable
760
tray runs, or between cable tray runs and equipment are permitted,
single conductor cables can be installed in accordance with the
725.154(C) and Power-limited tray cable
725.179(E) and 725,71 (F)
following; (a) 1/0 AWG and larger listed and marked for use in cable trays.
Author's Comment: For permitted cable types, see 501.10, 502.10.503.10, 504,20, and 505.15.
sive áreas, and in áreas requiring voltage isolation.
Cable tray systems aren't per-
The system must provide for the support of the cables and raceways in accordance with their corresponding articles. A bonding jumper, sized in accordance with 250.102 and installed in
Rigid metal conduit
344
accordance with 250.96, must bond the sections of cable tray, orthe
Service-entrance cable
338
cable tray and the raceway or equipment
Signaling raceway
725
(B) Completed Before Instaliation. Each run of cable tray must be
Underground feeder and branch-circuit cable
340
completed before the instaliation of cables or conductors.
406
Mike Holfs lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
392.56
Cable Trays
Through Partitions and Walls. Cable trays can extend through
Boxes and conduit bodies attached to the bottom or side of a cable
lons and walls, or vertically through platforms and floors if the
tray system must be fastened and supported in accordance with
llation is made in accordance with the firestopping requirements
314.23.
].21. (E) Exposed and Accessible. Cable trays must be exposed and accessible, except as permitted by 392.10(H). (F) Adequate Access. Sufficient space must be provided and maintaiíied about cable trays to permit adequate access for installing and
392.20 Cable and Conductor Instaliation (C) Connected in Parallel. To prevent unbalanced current in the parallel conductors due to inductive reactance, all circuit conductors of a parallel set [310.10(H)] must be bundied together and secured to prevent excessive movement due to fault current magnetic torces.
íPaintaining the cables. (G) Raceways, Cables, and Boxes Supported from Cable Trays. h industrial facilities where conditions of maintenance and supervi-
(D) Single Conductors. Single conductors of a circuit not connected in parallel must be installed in a single layer, unless the conductors are bound together.
sión ensure only qualified persons will service the instaliation, and if the cable tray system is designed and installed to support the load,
392.22 Number of Conductors or Cables.
cable tray systems can support raceways, cables, boxes, and conduit (A) Number of Muíticonductor Cables ín Cable Trays. The number
3. Figure 392-3
of muíticonductor cables, rated 2,000 volts or less, permitted in a single cable tray must not exceed the requirements of this secCable Tray - Support Raceways a n d B o x e s 392.18(G)
t
Cable Tray
I
Raceways, cables, boxes, and conduit bodies can be supported to a cable tray w h e r e only qualified persons will service t h e instaliation.
tion. The conductor sizes herein apply to both aluminum and copper conductors. (1) Any Mixture of Cables. If ladder or ventilated trough cable trays contain muíticonductor power or lighting cables, the máximum number of cables must conform to the following: (a) If all of the cables are 4/0 AWG and larger, the sum of the diameters of all cables must not exceed the cable tray width, and the cables must be installed in a single layer.
392.30 Securing and Supporting. (A) Fastened Secureiy. Cables installed vertically must be secureiy Copyright 2011, www.MkeHott-CCHn
Figure 392-3
fastened to transverso members of the cable tray. (B) Support. Supports for cable trays must be provided to prevent stress on cables where they enter raceways or other enclosures from cable tray systems. Cable trays must be supported in accordance with
For raceways terminating at the tray, a listed cable tray clamp or adapter must be used to secureiy fasten the raceway to the cable
the manufacturer's instaliation instructions.
tray system. The raceway must be supported in accordance with the
392.46 Bushed Raceway.
appropriate raceway article.
or conductors exit a bushed raceway used for the support or protec-
A box isn't required where cables
tion of the conductors. Raceways or cables running parallel to the cable tray system can be attached to the bottom or side of a cable tray system. The raceway or
392.56 Cable Spiices.
cable must be fastened and supported in accordance with the appro-
the spiice is accessible and insulated by a method approved by the
priate raceway or cable's Code article.
authority having jurisdiction. Spiices can project above the side ralis
Spiices are permiüed in a cable tray if
of the cable tray if not subject to physical damage. Figure 392-4
Mike Holt Enterprises, Inc. • www.MikeHoltcom • 888.NEC.C0DE (632.2633)
Cable Trays
392.60
s p i i c e s in Cable Tray 392.56
Metal cable trays containing Communications, data, and signaling conductors and cables must be eiectrically continuous through listed connections or the use of a bonding jumper not smaller than 10 AWG.
Cable Tray
Figure 392-6
Equipment Grounding Conductor Metallic Cable Trays 392.60m Spiices are permitted in a cable tray if the spiice is accessible and insulated by a method a p p r o v e d by the A H J . Spiices can project above the side ralis of the cable tray w h e r e not subject to physical d a m a g e . Copyngnt 2011. * w * MifcoHon.com
Figure 392-4
392,60 Equipment Grounding Conductor. (A) Metallic Cable Trays. Metallic cable trays can be used as equip-
Metal cable trays containing onlv non-power conductors must be eiectrically continuous. through approved connections or the use of a bonding jumper not smaller than 1 0 A W G .
ment grounding conductors where continuous maintenance and supervisión ensure that qualified persons service the installed cable
Figure 392-6
tray system. Figure 392-5 Author's Comment: Nonconductive coatings such as paint, Equipment Grounding Conductor Metallic Cable Trays 392.60(A)
lacquer, and enamel on equipment must be removed to ensure an effective ground-fault current path, or the termination fittings must be designed so as to make such removal unnecessary [250.12].
I
Bonding ; Conductor
Metal cable tray can be used as an equipment grounding conductor where continuous maintenance and supervisión ensure that only qualified persons service the cable tray.
(B) Serve as Equipment Grounding Conductor. Metal cable trays can serve as equipment grounding conductors where the following requirements have been met [392.10(0)]: (1) Cable tray sections and fittings are identified for grounding. Figure 392-7 Author's Comment: Identification will be marked on each cable tray section.
Copyngril 2011. www.MrkeHan.com
(4) Cable tray sections, fittíngs, and connected raceways are effec-
Figure 392-5
tively bonded to each other to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed
The metallic cable trays that support conductors must be bonded
on them [250.96(A)]. This is accomplished by using bolted
together to ensure that they have the capacity to conduct safely any
mechanical connectors or bonding jumpers sized in accordance
fault current likely to be imposed in accordance with 250.96(A).
with 250.102.
408
Mike HoiVs iiiustrated Guide to Understanding tiie 2011 Nationai Eiectricai Code, Voiume 1
392.80
Cable Trays
Metallic Cable Trays - Serve a s Equipment Grounding Conductor 392.60(B}(1)
392.80 Ampacity of Conductors. (A) Ampacity in Cable Trays. (1) The allowable
Bonding Conductor
Steel or a l u m i n u m cable tray systems can serve as a n E G C w h e n cable tray sections and fittings are identified for grounding and are bonded t o each other.
ampacity
of muíticonductor
cables
installed
according to the requirements of 392.22(A) must be as given in Table 310.15(B)(16) and Table 310.15(B)(18). (a) The conductor ampacity adjustment factors of 310.15(B){3)(a) apply to a given cable if it contains more than three current-carrying conductors. The conductor adjustment factors only apply to the number of current-carrying conductors in the cable and not to the number of conductors in the cable tray.
Copynghl 20Í1. www.HikeHon.coni
Figure 392-7
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409
CHAPTER
3
Practice Questions
These questions are based on tiie 2011 National Electrical Code. Please use ttie 2011 NEC Code bool< to answer tlie following questions.
4.
Where cables and nonmetallic raceways are installed parallel to framing members, the nearest outside surface of the cable or raceway shall be
the nearest edge of the framing
member where nails or screws are likely to penétrate. (a) not less than iy4 in. from
CHAPTER 3. WIRING METHODS AND MATERIALS
(b) immediately adjacent to (c) not less than 1/16 in. from (d) 90°away from
Article 300. Wiring Methods 1.
Conductors shall be installed within a raceway, cable, or enclo-
5.
When installed under metal-corrugated sheet roof decking, the rules for spacing from roof decking apply equally to rigid metal
sure.
conduit and intermedíate metal conduit. (a) True (a) True
(b) False
(b) False 2.
Where cables or nonmetallic raceways are installed through bored holes in joists, rafters, or wood members, holes shall be bored so that the edge of the hole is
6.
What is the minimum cover requirement for direct burial Type UF cable installed outdoors that supplies a 120V, 30A circuit?
the nearest edge of
the wood member.
(a) 6 in.
(a) not less than VA in. from
(b) 1 2 i n .
(b) immediately adjacent to
(c) 18 in.
(c) not less than 1/16 in. from
(d) 24 in.
(d) 90° away from 7. 3.
What is the minimum cover requirement for Type UF cable
Where Type NM cables pass through cut or drilled slots or
suppiying power to a 120V, 15A GFCI-protected circuit outdoors
holes in metal members, the cable shall be protected by
under a driveway oí a one-family dweiling?
which are installed in the opening prior to the instaliation of the
(a) 6 in.
cable and which secureiy cover all metal edges.
(b) 1 2 i n .
(a) listed bushings
(c) 16 in.
(b) listed grommets
(d) 24 in.
(c) plates (d) a or b 8.
The interior of underground raceways shall be considered a location. (a) wet (b) dry (c) damp (d) corrosive
410
Mike HolVs lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Article 300
Practice Questions
Direct-buried service conductors that are not encased in
14.
Where nonmetallic wiring methods are subject to exposure to
concrete and that are buried 18 in. or more below/ grade shall
chemical solvents or vapors, they shall be inherently resistant
have their locahon identified by a warning ribbon placed in the
to chemicals based upon their being
trench at Ieast
above the underground instaliation.
.
(a) listed for the chemical
(a) 6 in.
(b) identified for the chemical
(b) 10in.
(c) a and b
(c) 12in.
(d) a or b
(d}18in. 15. 10.
Conduits or raceways through which moisture may contact live parts shall be
Where portions of a cable raceway or sieeve are subjected to different temperatures and condensation is known to be a
at either or both ends.
probiem, the
shall be filled with an approved material
(a) sealed
to prevent the circulation of warm air to a colder section of the
(b) plugged
raceway or sieeve.
(c) bushed
(a) raceway
(d) a or b
(b) sieeve (c) a or b
11.
Each direct-buried single conductor cable must be located
(d) none of these
in the trench to the other single conductor cables in the same parallel set of conductors, inciuding equipment grounding 16.
conductors.
Where raceways are installed in wet locations above grade, the interior of these raceways shall be considered a
(a) perpendicular
loca-
tion.
(b) bundied together (c) in cióse proximity
(a) wet
(d) spaced apart
(b) dry (c) damp
12.
(d) corrosive
Raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware shall be of materiais suitable for
17.
.
Where independent support wires of a ceiling assembiy are used to support raceways, cable assemblies, or boxes above a
(a) corrosive locations
ceiling, they shall be secured at
(b) wet locations
(a) one
(c) the environment in which they are to be installed
(b) both
(d) none of these
(c) a or b
ends.
(d) none of these 13.
Ferrous metal raceways, boxes, fittings, supports, and support hardware can be installed in concrete or In direct contact with the earth or other áreas subject to severe corrosive influences, where
approved for the conditions.
18.
Ceiling-support wires used for the support of electrical raceways and cables within nonfire-rated assemblies shall be distinguishable from the suspended-ceiling framing support
(a) the soil is
wires.
(b) made of material
(a) True
(c) the qualified installer is
(b) False
(d) none of these
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411
Article 310
19.
Practice Questions
Metal or nonmetallic raceways, cable armors, and cable sheaths
20.
25.
between cabinets, boxes, fittings or other
Electrical installations in hollow spaces, vertical shafts, and ventilation or air-handling ducts shall be made so that the
enclosures or outlets.
possible spread of fire or products of combustión is not
(a) can be attached with electrical tape
(a) substantially increased
(b) are allowed gaps for expansión
(b) allowed
(c) shall be continuous
(c) inherent
(d) none of these
(d) possible
In multiwire branch circuits, the continuity of the
26.
.
Equipment and devices shall only be permitted within ducts or plenum chambers specifically fabricated to transport environ-
conductor shall not be dependent upon the device connections.
mental air if necessary for their direct action upon, or sensing
(a) ungrounded
of, the
(b) grounded
.
(c) grounding electrode
(a) contained air
(d) a a n d b
(b) air quality (c) air temperature (d) none of these
21.
A box or conduit body shall not be required where cables enter or exit from conduit or tubing that is used to provide cable support or protection against physical damage.
27.
shall be permitted to support the wiring methods and equipment permitted to be used in other spaces used for envi-
(a) True
ronmental air (plenum).
(b) False
(a) Metal cable tray system (b) Nonmetallic wireways 22.
A bushing shall be permitted in lieu of a box or terminal where
(c) PVC conduit
the conductors emerge from a raceway and enter or terminate
(d) Surface nonmetallic raceways
at equipment such as open switchboards, unenclosed control equipment, or similar equipment.
Article 310. Conductors for General Wiring
(a) True (b) False
1.
In general, the minimum size conductor permitted for use in parallel installations is
23.
AWG.
Prewired raceway assemblies shall be used only where specifi(a) 10
cally permitted in the A/fCfor the applicable wiring method.
(b) 4
24.
(a) True
(c) 1
(b) False
(d) 1/0
A vertical run of 4/0 AWG copper shall be supported at intervals not exceeding
.
2.
Where conductors in parallel are run in sepárate raceways, the raceways shall have the same electrical characteristics.
(a) 4 0 f t
(a) True
(b) 80 ft (c) IOOft
(b) False
(d) 120ft
412
Mike Hoit's iilustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Article 314
Practice Questions
3.
There are four principal determinants of conductor operating temperature, one of which is
8.
generated internally in the
THWN insulated conductors are rated
.
(a) 75°C
conductor as the result ot load current flow, inciuding funda-
(b) for wet locations
mental and harmonio currents.
(c) a and b
(a) friction
(d) not enough information
(b) magnetism (c) heat 9.
(d) none of these
The minimum size conductor permitted for branch circuits under 600V is
AWG.
(a) 14 4.
Each current-carrying conductor of a paralleled set of conduc-
(b) 12
tors shall be counted as a current-carrying conductor for the
(c) 10
purpose of appiying the adjustment factors of 310.15(B)(3)(a).
(d) 8
(a) True (b) False
5.
When bare conductors are installed with insulated conductors, their ampacities shall be limited to
.
Article 312. Cabinets, Cutout Boxes, and IVIeter Socicet Enclosures 1.
Where raceways or cables enter above the level of uninsulated
(a) 60°C
live parts of cabinets, cutout boxes, and meter socket enclo-
(b) 7 5 X
sures in a wet location, a(n)
(c) 90°C
shall be used.
(a) fitting listed for wet locations
(d) the lowest temperature rating for any of the insulated
(b) explosionproof seal
conductors
(c) fitting listed for damp locations (d) insulated fitting
6.
On a three-phase, 4-wire, wye circuit, where the major portion of the load consists of nonlinear loads, the neutral conductor
2.
Each cable entering a cutout box
.
shall be counted when appiying 310.15(B)(3)(a) adjustment (a) shall be secured to the cutout box
factors.
(b) can be sieeved through a chase (a) True
(c) shall have a máximum of two cables per connector
(b) False
7.
(d) all of these
When determining the number of current-carrying conductors, a grounding or bonding conductor shall not be counted when appiying the provisions of 310.15(B)(3)ta) (a) True
.
Article 314. Outlet, Device, Pulí and Junction Boxes; Conduit Bodies; Fittíngs; and Handhole Enclosures 1.
According to the NEC, the volume of a 3 x 2 x 2 in. device box is
(b) False (a) 8 cu in. (b) 10 cu in. (c) 12 cu in. (d) 14 cu in.
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413
Article 314
2.
Practice Questions
When couníing the number of conductors in a box, a conductor
7.
running through the box with an unbrol^en loop or coil not less
.
(a) cover
than twice the minimum length required for free conductors shall be counted as
In completed installations, each outlet box shall have a
(b) faceplate
conductor(s).
(c) canopy
(a) one
(d) any of these
(b) two (c) three 8.
(d) four
Listed outlet boxes to support ceiling-suspended fans ttiat weigh more than
Ib shall have the máximum allowable
weight marked on the box. 3.
For the purposes of determining box fill, each device or utiliza-
(a) 35 Ib
tion equipment in the box which is wider than a single device box counts as two conductors for each
(b) 50 Ib
required for the
(c) 60 Ib
mounting.
(d) 70 Ib
(a) inch (b) kilometer 9.
(c) gang (d) box
Power distribution biocks shall be permitted in pulí and junction boxes over 100 cubic inches when they comply with the provi-
""^
sions of 314.28(E). (a) True 4.
Conduit bodies that are durably and legibly marked by the
(b) False
manufacturer with their volume can contain spiices, taps, or devices. 10.
(a) True
shall be installed so that the wiring contained can be rendered accessible without removing any part of the building
(b) False
or, in underground circuits, without excavating sidewaiks, paving, or earth. 5.
Noncombustible surfaces that are broken or incompleto around
(a) Boxes
boxes employing a flush-type cover or faceplate shall be
(b) Conduit bodies
repaired so there will be no gaps or open spaces larger than
(c) Handhole enclosures
at the edge of the box.
(d) all of these
{a)1/16in. (b) 1/8 in. (c)
1/4
in.
(d)
1/2
in.
11.
Conductors, spiices or terminations in a handhole enclosure shall be listed as
.
(a) suitable for wet locations (b) suitable for damp locations 6.
A wood brace used for supporting a box for structural mounting shall have a cross-section not less than nominal
.
(c) suitable for direct burial in the earth (d) none of these
(a) 1 in. X 2 in. (b) 2 i n . x 2 i n . (c) 2 i n . x 3 i n . (d) 2 in. X 4 in.
414
Mike HolVs lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Practice Questions
Article 330
icie 320. Armored Cable (Type AC) Type
Article 330. IVIetal-Clad Cable (Type MC)
cable is a fabricated assembiy of insulated
1.
conductors in a flexible interlocked metallic armor.
Type
is a factory assembiy of insulated circuit conduc-
tors within an armor of interlocking metal tape, or a smooth or corrugated metallic sheath.
(a) AC (b) MC
(a) AC
(c) NM
(b) MC
(d) b and c
(c) NM (d) b and c
Armored cable shall not be installed
. 2.
(a) in damp or wet locations
Smooth-Sheath Type MC cable with an external diameter not greater than
(b) where subject to physical damage
in. shall have a bending radius not more than
times the cable external diameter.
(c) where exposed to corrosive conditions (d) all of these
(a) five tb)10 (c) 12
3.
When Type AC cable is run across the top of a floor joist in an
(cl)13
attic without permanent ladders or stairs, substantial guard strips within
of the scuttie hole, or attic entrance, shall
protect the cable.
3.
Type MC cable shall be secured at intervals not exceeding
(a) 3ft (b) 4ft
(a) 3ft
{c)5ft
(b) 4ft
(d)6tt
(c) 6ft (d) 8ft
4.
Type AC cable can be supported and secured by
. 4.
(a) Staples (b) cable ties
Fittings used for connecting Type MC cable to boxes, cabinets, or other equipment shall
.
(c) straps
(a) be nonmetallic only
(d) all of these
(b) be listed and identified for such use (c) be listed and identified as weatherproof (d) include anti-shorting bushings
5.
Armored cable used to connect recessed luminaires or equipment within an accessible ceiling can be unsecured for lengths up to
.
(a) 2 f t (b) 3ft (c) 4V2ft (d) 6ft
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415
Article 334
Practice Questions
Article 334. Nonmetallic-Slieathed Cable (Types NM and NMC)
6.
For Type NM and NMC cable, the conductor ampacity used for ambient temperature correction [310.15(BK2){a}], conductor bundiing adjustment [310.15(B)(3)(a)], or both, is based on
1.
Type
the 90^0 conductor insulation rating [310.15(B)(2)], provided
cable is a wiring method that endoses two or
the adjusted or corrected ampacity doesn't exceed that for a
more insulated conductors within a nonmetallic jacket.
rated conductor.
(a) AC (b) MC
(a) 60°C
(c) NM
(b) 75°C
(d) b and c
(c) 9 0 X (d) 120°C
2.
Type NM and Type NMC cables shall be permitted in
.
(a) in one- and two-family dweilings and their attached/
Article 338. Service-Entrance Cable (Types SE and USE)
detached garages or storage buildings (b) multifamily dweilings permitted to be of Types III, IV, and V
1.
Type SE cable shall be permitted to be used as
in wiring
systems where all of the circuit conductors of the cable are of
construction
the thermoset or thermoplastic type.
(c) other structures permitted to be of Types III, IV, and V construction, except as prohibited in 334.12.
(a) branch circuits
(d) any of these
(b) feeders (c) a or b
3.
(d) neither a or b
Type NM cable shall closely follow the surface ot the building finish or running boards when run exposed. 2.
(a) True
Type USE cable is not permitted for
(b) False
wiring.
(a) underground (b) interior
4.
(c) a or b
Where Type NM cable is run at angles with joists in unfinished
(d) a and b
basements and crawl spaces, it is permissible to secure cables not smaller than
conductors directly to the lower edges
of the joist.
Article 340. Underground Feeder and Branch-Circuit Cable (Type UF)
(a) two, 6 AWG (b) three, 8 AWG (c) three, 10 AWG
1.
Type
(d) a or b
an overall covering of nonmetallic material suitable for direct -
5.
burial in the earth.
Type NM cable protected from physical damage by a raceway
(a) NM
shall not be required to be
(b) UF
(a) covered (b) insulated
cable is a factory assembiy of conductors with
within the raceway
(c) SE (d) TC
(c) secured (d) unspiiced
416
Mike HoiVs Iliustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Practice Questions
2.
Article 344
Type UF cable can be used in commercial garages.
4.
Threadless couplings approved for use with IMC in wet locations shall be
(a) True (b) False
.
(a) rainproof (b) listed for wet locations (c) moistureproof
3.
Type UF cable shall not be used where subject to physical
(d) concrete-tight
damage. (a) True
Article 344. Rigid Metal Conduit (Type RMC)
(b) False
1. 4.
The overall covering of Type UF cable is
.
Galvanized steel, stainless steel and red brass RMC can be installed in concrete, in direct contact with the earth, or in áreas subject to severe corrosive influences when protected by
(a) fíame retardant
and judged suitable for the condition.
(b) moisture, fungus, and corrosión resistant (c) suitable for direct burial in the earth
(a) ceramic
(d) all of these
(b) corrosión protection (c) backfill (d) a natural barrier
Article 342. Intermediate IVIetal Conduit (Type IMC) 1.
IMC can be installed in or under cinder fill subject to permanent moisture
2.
Aluminum fittings and enclosures can be used with conduit where not subject to severe corrosive influences.
.
(a) where the conduit is not less than 18 in. under the fill
(a) steel rigid metal
(b) when protected on all sides by 2 in. of noncinder concrete
(b) aluminum rigid metal
(c) where protected by corrosión protection judged suitable for
(c) PVC-coated rigid conduit only (d) a and b
the condition (d) any of these 3. 2.
Cut ends of RMC shall be
or otherwise finished to
remove rough edges.
A run of IMC shall not contain more than the equivalent of quarter bends between pulí points such as conduit
(a) threaded
bodies and boxes.
(b) reamad
(a) one
(c) painted
(b) two
(d) galvanized
(c) three (d) four 4.
Threadless couplings and connectors used with RMC buried in masonry or concrete shall be the
3.
Trade size 1 IMC shall be supported at intervals not exceeding
type.
(a) raintight (b) wet and damp location
(a) 8 f t
(c) nonabsorbent
(b) 10ft
(d) concrete-tight
(c) 12 ft (d) 14ft
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417
Article 348
5.
Practice Questions
Each length of RMC shall be clearly and durably identified in every
.
(a) 3 f t
Article 350. Liquidtight Flexible Metal Conduit (Type LFMC) 1.
(b) 5 f t
Liquidtight flexible metal conduit must be secureiy fastened by a means approved by the authority having jurisdiction within
(c) 10 ft
of termination.
(d) 20 ft
(a) 6 in. (b) 1 0 i n .
Article 348. Flexible Metal Conduit (Type FMC)
(c) 1 ft (d) 1 0 f t
1.
FMC can be installed exposed or concealed where not subject to physical damage. 2.
For liquidtight flexible metal conduit, if flexibility is necessary
(a) True
after instaliation, unsecured lengths from the last point the
(b) False
raceway is secureiy fastened must not exceed
.
(a) 3 ft for trade sizes Vi through 1 2.
Cut ends of FMC shall be trimmed or otherwise finished to
(b) 4 ft for trade sizes 1 Vz through 2
remove rough edges, except where fittings
(c) 5 ft for trade sizes 2 Vi and larger
.
(d) allof these
(a) are the crimp-on type (b) thread into the convolutions (c) contain insulated throats
3.
(d) are listed for grounding
Where flexibility
, liquidtight flexible metal conduit shall
be permitted to be used as an equipment grounding conductor when installed in accordance with 250.118(6).
3.
Flexible metal conduit shall not be required to be
(a) is required after instaliation
where
fished between access points through concealed spaces in
(b) is not required after instaliation
finished buildings or structures and supporting is impracti-
(c) either a or d
cable.
(d) is optional
(a) secured (b) supported
Article 352. Rigid Polyvinyl Chioride Conduit (Type PVC)
(c) complete (d) (a) and (b)
1.
PVC conduit shall be permitted for exposed work where subject to physical damage if identified for such use.
4.
In an FMC instaliation, concealed.
connectors shall not be
(a) True (b) False
(a) straight (b) angle (c) grounding-type (d) none of these
418
mke Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Questions
Article 362
PVC conduit shall not be used
, unless specifically
2.
permitted.
Bends in LFNC shall
between pulí points.
(a) not be made
(a) in hazardous (classified) locations
(b) not be limited in degrees
(b) for the support of luminaires or other equipment
(c) be limited to 360 degrees
(c) where subject to physical damage unless identified for such
(d) be limited to 180 degrees
use (d) allof these
Article 358. Electrical Metallic Tubing (Type EMT) Bends in PVC conduit shall
between pulí points.
1.
is a listed thin-wail, metallic tubing of circular cross
(a) not be made
section used for the instaliation and physical protection of elec-
(b) not be limited in degrees
trical conductors when joined together with listed fittings.
(c) be limited to 360 degrees
(a) LFNC
(d) be limited to 180 degrees
(b) EMT (c) NUCC
4,
(d) RTRC
Where PVC conduit enters a box, fitting, or other enclosure, a bushing or adapter shall be provided to protect the conductor from abrasión unless the design of the box, fitting, or enclosure
2.
affords equivalent protection.
When EMT is installed in wet locations, all supports, bolts, straps, and screws shall be
(a) True
.
(a) of corrosion-resistant materiais
(b) False
(b) protected against corrosión (c) a or b
5.
(d) of nonmetallic materiais only
PVC conduit and fittings for use above ground shall have the following characteristics
. 3.
(a) fíame retardant (b) resistance to low temperatures and sunlight
EMT shall not be threaded. (a) True
(c) resistance to distortion from heat
(b) False
(d) allof these
Article 362. Electrical Nonmetallic Tubing (Type ENT)
Article 356. Liquidtight Flexible Nonmetallic Conduit (Type LFNC)
1.
ENT is composed of a material resistant to moisture and chemical atmospheres, and is
1.
LFNC shall be permitted for
.
. (a) flexible
(a) direct burial where listed and marked for the purpose
(b) fíame retardant
(b) exposed work
(c) fireprooí
(c) outdoors where listed and marked for this purpose
(d) flammable
(d) all of these
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419
Article 376
Practice Questions .iS-MfíU-í. • •
2.
When a building is supplied with a fire sprinkier system, ENT
Article 376. I\1etal Wireways
can be installed above any suspended ceiling. 1.
(a) True
Metal wireways are sheet metal troughs with
for
housing and protecting electric conductors and cable.
(b) False
(a) removable covers (b) hinged covers 3.
ENT is not permitted in hazardous (classihed) locations, unless
(c) a or b
permitted in other articles of the Code.
(d) none of these
(a) True (b) False
2.
Wireways can pass transversely through a wall
.
(a) if the length passing through the wall is unbroken 4.
ENT shall not be used where exposed to the direct rays of the
(b) if the wall is of fire-rated construction
sun, unless identified as
(c) in hazardous {classified) locations
.
(d) if the wall is not of fire-rated construction
(a) high-temperature rated (b) sunlight resistant (c) Schedule 80
3.
(d) never can be
5.
The sum of the cross-sectional áreas of all contained conductors at any cross-section of a metal wireway shall not exceed
Cut ends of ENT shall be trimmed inside and
to remove
(a) 50 percent
rough edges.
(b) 20 percent
(a) outside
(c) 25 percent
(b) tapered
(d) 80 percent
(c) filed (d) beveled
4.
Where insulated conductors are deflected within a metal wireway, the wireway shall be sized to meet the bending
6.
Bushings or adapters shall be provided at ENT terminations to
requirements corresponding to
protect the conductors from abrasión, unless the box, fitting, or
Table 312.6(A).
enclosure design provides equivalent protection.
(a) one
(a) True
(b) hwo
(b) False
(c) three
wire per terminal in
(d) four 7.
The
of conductors used in prewired ENT manufactured
assemblies shall be identified by means of a printed tag or
5.
Power distribution biocks installed in metal wireways shall
label attached to each end of the manufactured assembiy.
420
(a) type
(a) allow for sufficient wire-bending space at termináis
(b) size
(b) not have uninsulated exposed live parts
(c) quantity
(c) a or b
(d) all of these
(d) a and b
Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
Practice Questions
Article 392
Article 380. IVIultioutlet Assembiy
5.
Surface metal raceway enclosures providing a transition from other wiring methods shall have a means for connecting a(n)
1.
A multioutlet assembiy shall not be installed. (a) in hoistways
(a) grounded conductor
(b) where subject to severe physical damage
(b) ungrounded conductor
(c) where subject to corrosive vapors
(c) equipment grounding conductor
(d) all of these
(d) allof these
Article 386. Surface Metal Raceways
Article 392. Cable Trays
1.
1.
Unbroken lengths of surface metal raceways can be run through dry
.
A cable tray is a unit or assembiy of units or sections and associated fittings forming a
system used to secureiy fasten
or support cables and raceways.
(a) walls (b) partitions
(a) structural
(c) floors
(b) flexible
(d) all of these
(c) movable (d) secure
2.
The voltage between conductors in a surface metal raceway shall not exceed
unless the metal has a thickness of not
2.
less than 0.040 in. nominal.
Where exposed to the direct rays of the sun, insulated conductors and jacketed cables installed in cable trays shall be as being sunlight resistant.
(a) 150V (b) 300V
(a) listed
(c) 600V
(b) approved
(d) 1,000V
(c) identified (d) none of these
3.
The máximum number of conductors permitted in any surface raceway shall be
.
3.
Any of the following wiring methods can be installed in a cable tray:
(a) no more than 30 percent of the inside diameter (b) no greater than the number for which it was designed
(a) metal raceways
(c) no more than 75 percent of the cross-sectional área
(b) nonmetallic raceways
(d) that which is permitted in Table 312.6(A)
(c) cables (d) allof these
4.
Surface metal raceways shall be secured and supported at intervals
.
(a) in accordance with the manufacturer's instaliation instructions
4.
Each run of cable tray shall be
before the instaliation of
cables. (a) tested for 25 ohms resistance
(b) appropriate for the building design
(b) insulated
(c) not exceeding 4 ft
(c) completed
(d) not exceeding 8 ft
(d) all of these
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421
Article 392
5.
Practice Questions
In industrial facilities where conditions of maintenance and
8.
Metal cable trays containing only non-power conductors such
supervisión ensure that only qualified persons will service the
as communication, data, signal, conductors and cables must be
instaliation, cable tray systems can be used to support
eiectrically continuous, through listed connections or the use of
.
an insulated stranded bonding jumper not smaller than
(a) raceways (b) cables
(a) 12 AWG
{c} boxes and conduit bodies
(b) 10 AWG
(d) allof these
(c) 6AWG
.
(d) 4AWG 6.
Where single conductor cables comprising each phase, neutral, or grounded conductor of a circuit are connected in parallel in a cable tray, the conductors shall be installed
9.
, to prevent
Steel or aluminum cable tray systems shall be permitted to be used as an equipment grounding conductor, provided the cable
current unbalance in the paralleled conductors due to inductive
tray sections and fittings are identified as
reactance.
requirements.
(a) in groups consisting of not more than three conductors per
(a) an equipment grounding conductor
phase or neutral
, among other
(b) special
(b) in groups consishng of not more than one conductor per
(c) industrial
phase or neutral
(d) all of these
(c) as individual conductors secureiy bound to the cable tray (d) in sepárate groups 10.
Cable trays shall
.
(a) include fittings or other suitable means for changes in direc7.
A box shall not be required where cables or conductors from cable trays are installed in bushed conduit and tubing used as support or for protection against (a) abuse
.
tion and elevation (b) have side ralis or equivalent structural members (c) be made of corrosion-resistant material or protected from corrosión as required by 300.6
(b) unauthorized access
(d) allof these
(c) physical damage (d) tampering
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Mike Holt's lllustrated Guide to Understanding the 2011 National Electrical Code, Volume 1
