MOTOR CIRCUITS, AND CONTROLLERS based on Phil. Electrical Code part 1 with reference to product standards
Prepared by : Gem Tan Fuji-Haya Audit Inspection & Maintenance Corp.
\u2022Why need Philippine Electrical Code ( PEC )? \u2022What is the purpose of PEC?
\u2022 The purpose of PEC is the practical safeguarding of persons and property from hazards arising from the use of electricity.
\u2022 The code contains provisions that are considered the minimum requirements necessary for safety. Compliance therewith and proper maintenance will result in an installation that is essentially free from hazard but not necessary efficient, convenient, or adequate for good service or future expansion of electrical use.
Approach to Electrical Safety Installation Code (PEC) Provide the best technical information, ensuring the practical safeguarding of persons & property from the hazards.
Product Standards & Certification Design & test requirement assure that it can be relied on the function safely.
Safe Products & Safe Installation
Inspection & Enforcement Understand the relationship between the product standards and installation codes.
Motor Protection
Any device using electrical energy could malfunction du an electrical problem:
- overvoltage, undervoltage, phase imbalance or single-phasi ( phase loss ),
- short-circuits which can surpass the breaking capacity of t contactor. a mechanical problem:
- stalled rotor, momentary or prolonged overload.
Basic Protection Schemes Range 1.05 - 1.20 In Circuit breaker contactor
Characteristic of thermal relay
t
Cable thermal-withstan limit 1 to 10 s
Limit of thermalrelay constraint
Thermal relay
motor
20 to 30 ms In
Is
I”
short-ckt current breaking capacity
What Current To Use ? Sec. 4.30.1.6
For general motor applications (excluding applications of torque motors and sealed hermetic-type refrigeration motor-compresso current rating shall be based on the following:
(1) Table Values. The values given in Table 4.30.14.1 to 4.30.14.4, including notes, shall be used to determine the ampacity of conductors or ampere ratings of switches, branc circuit short circuit & ground-fault protection, instead of actua current rating marked on the motor nameplate. (2) Nameplate Values. Separate motor overload protection shall be based on the motor nameplate current rating.
What Current To Use ? Sec. 4.30.1.6(b) Torque Motors. For torque motors, the rated current shall be locked-rotor current, & this nameplate current shall be used to determine the ampacity of the branch-circuit conductors covered in Sec. 4.30.2.2 (Single Motor) & 4.30.2.4 (Several Motors or a Motor & other Load. The ampere rating of motor overload protection, & the ampere rating of motor branch-circuit short-circuit & ground-fault protection in accordance with Sec. 4.30.4.2(b).
What Current To Use ? Sec. 4.40.1.6(a) Hermetic Refrigerant Motor-Compressor. The rated-load current marked on the nameplate of the equipment in which the motor-compressor is employed shall be used in determining the rating or ampacity of the disconnecting means, the branch-circuit conductors, the controller, the branch circuit short circuit & ground fault protection & the separate motor overload protection. Where no rated-load current shown on the equipment nameplate, the rated-load current shown on the compressor nameplate shall be used.
Motor Circuit Conductors Sec. 4.30.2.2(a) Branch Circuit Short Circuit & Ground Fault Protection Motor Controller Overload Protection Motor p582
Single Motor. - General Branch-circuit conductors that supply a single motor used in a continuous duty Branch Circuit application shall have an Conductors ampacity of not less than 125% of the motor’s full-load current rating .
Ampacity Table
FPN: Tables 3.10.1.16 through 3.10.1.19 are application tables for use in determining conductor sizes on loads calculated in accordance with Article 2.20. Allowable ampacities result from consideration of one or more of the following: 1. Temperature compatibility with connected equipment, especially at the connection points.
2. Coo rdinat ion with circuit and system overcurrent protection 3. Compliance with the requirements of product listings or certifications. 4. Preservation of the safety benefits of established industry practices and standardized procedures.
Temperature Limitations Sec. 1.10.1.14 (c) The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for termination’s shall be permitted to be used for ampacity adjustment, correction, or both.
Temperature Limitations Sec. 1.10.1.14 (c) (1) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 2.0 mm2 (1.6 mm dia.) through mm2 conductors, shall be used only for one of the following. a. Conductors rated 60oC, or b. Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60 ampacity of the conductor size used, or
c. Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors, or
d. For motors marked with design letters B, C, D, or E, conductors having an insulation rating of 75oC or higher sha permitted to be used provided the ampacity of such conduct
NEMA Motor Design-Letters Classification NEMA Classes A NEMA Classes B NEMA Classes C NEMA Classes D NEMA Classes F
Temperature Limitations Sec. 1.10.1.14 (c)
(2) Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 38 mm2, shall be used only for a. Conductors rated 75oC, or
b. Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75oC ampa of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conduct
Minimum Branch Circuit Conductor Size Sec. 2.10.2.1(a)
The minimum branch circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity equal to or greater than the noncontinuous load plus 125% of the continuous load.
Exception: Where the assembly, including the overcurrent devices protecting the branch circuit, is listed for operation at 100% of its rating, the ampacity of the branch circuit conductors shall be permitted to be not less than the sum of t continuous load plus the noncontinuous load.
MCCB Temperature Test (Non 100% Rated) The temperature rise on a wiring terminal at point to which the insulation of a wire is brought up as in actual o service shall not exceed 50 C. The temperature rise on a circuit breaker, or an extension member, where a bus bar is to be connected shall not o exceed 50 C.
MCCB Temperature Test (Non 100% Rated)
If the temperature rise at the points where the connection are made exceed 50oC but not more than 65oC with the circuit breaker carrying 100% of rated current, the temperature test may be repeated using an untested circuit breaker installed in enclosure that is representative of the smallest enclosure with which the circuit breaker is likely to used. Under these conditions, with the circuit breaker carrying 80% of its maximum rated current, the temperature rise at the points where the connection to the external wires or bus bars are made sha not exceed 50oC.
MCCB Temperature Test (100% Rated)
The temperature rises (1) where connections are made to exte bus bars, when bus bar are used; or (2) on a wiring terminal a point to which the insulation of a wire is brought up as in actu o service when tested with insulated wire shall not exceed 60 C
Exception: The marking required need not be provided if the temperature rise measured on the insulated cable does not exc o 50 C.
Marking A circuit breaker that is intended to be operated continuously at 100% of its rating and that has a temperature rise on a wiring terminal exceeding o 50 C, shall be marked, A. For use with 90 C wire and the wire size. The o wire size shall be based on the ampacity of 75 C rated conductor. o
Over-current Protection For Conductors Circuit Breaker should be tested and wired in accordance with Table given in the Circuit Breaker Standard.
Caution:- The use of conductors smaller than those shown in Nema AB1 or ANSI/UL 489 Molded Case Circuit Breakers standard Table can result in unsafe conditions such as overheating and change in tripping characteristics; consult t manufacturer.
Temperature-rise Limits for Terminals Terminal material
Temp.-rise limits1) (K)
Bare copper
60
Bare brass
65
Tin plated copper or brass
65
Silver plated or nickel plated copper or brass
70
Other metals
2)
1)
The use in service of connected conductors significantly smaller than those listed in Table 9 & 10 could result in higher terminals & internal parts temperature & such conductors should not be used w/o the manufactur consent since higher temp. could lead to equipment failure. 2)
Temp-rise limits to be based on service experience or life tests but not to exceed 65K.
Motor Circuit Conductors Sec. 4.30.2.2(b)
Other than Continuous Duty. Conductors for a motor used in a short-time, intermittent, periodic, or varying duty application shall have an ampacity of not less than the percentage of the motor nameplate current shown in Table 4.30.2.2(b), unless the authority having jurisdiction grants special permission for the conductors of lower ampacity.
Sec 4.30.2.2(b) p583
Duty-Cycle Service Table 4.30.2.2(b) Classification of Service
Nameplate Current Rating Percentag 5-min. 15-min. 30&60 min. Cont.rate
Short time duty operating 110 valves, raising or lowering rolls, etc.
120
150
Intermittent duty freight & 85 passenger elevators, pumps, etc.
85
90
140
95
140
150
200
Periodic duty rolls, ore & coal85 90 handling machines, etc. Varying duty
110
120
-
Note:Any motor application shall be considered as continuous dut unless the nature of the apparatus it drives is such that the motor operate continuously with load under any condition of use.
Wound-Rotor Secondary Sec 4.30.2.3
Secondary conductor rated no Primary conductors rated less than 125% of full load Motor not less than 125% of secondary current or Table motor primary current 4.30.2.2(b)other than Cont. Du
Line
The ampacity of the conductors betwee controller and resistor shall not be less than that shown in Table 4.30.2.3(c).
Wound-Rotor Secondary Conductor Table 4.30.2.3(c) Resistor Duty Classification
Amp. of Conductor in % of Full lo Secondary Current
Light starting duty
35
Heavy starting duty
45
Extra heavy starting duty
55
Light intermittent duty
65
Medium intermittent duty
75
Heavy intermittent duty
85
Continuous duty
110
Thermal Devices Circuit breaker Motor Controller Overload Protection
motor
Thermal relays and other devices not designed to open short circuits or ground faults shall not be used for the protection of conductors against overcurrent due to short circuits or ground faults, but the use of such shall be permitted to protect motor branch circuit conductors from overload if protected in accordance with Sec.4.30.3.10
Overload Relays Sec.4.30.3.10 Overload relays and other devices for motor overload protection that are not capable of opening short circuits shall be protected by fuses or circuit breakers with rating or settings in accordance with Section 4.30.4.2.
Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 PEC 1 Table FLA
Motor Nameplate FLA GT Motor Ser.No. 123 Frame OPEN PF 75% EFF. 70% S.F. 1.15 PHASE 1 VOLTS 115/230 FLA 18.5/9.27 o C RISE 40 CYCLE 60 RPM 1725 DUTY CONT HP 1.5 CODE LETTER F
Table is used to size: •conductors & disconnects •short circuit & ground fault protective devices
Motor nameplate FLA is used to size overload protection
Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 Continuous-Duty Motors.
Each continuous duty motor shall be protected against overlo by a separate overload device that is responsive to motor curr This device shall be selected to trip or shall be rated at no mo than the following percent of the motor nameplate full-load current rating: Motors with a marked service factor not less than 1.15 125% o Motors with a marked temperature rise not over 40125% C All other motors 115%
Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 Continuous-Duty Motors.
Where a separate motor overload device is connected so that does not carry the total current designed on the motor namep such as for wye-delta starting, the proper percentage of the nameplate current applying the selection or setting of the overload device shall be clearly designated on the equipment, manufacturer’s selection table shall take this into account.
FPN: Where power factor correction capacitors are installed o the load side of the motor overload device, see Sec 4.60.1.9
Branch Circuit Overload Protection Sec. 4.30.3.2(a)1
Overload Relay?
Case 1
Case 2
Rating or Setting of Motor Overload Device Sec. 4.60.1.9 Capacitors with Motors. Rating or Setting of Motor Overload Device. Where a motor installation includes a capacitor connected on the lode side of the motor overload device, the rating or setting of the motor overload device shall be based on the improved power factor of the motor circuit. The effect of the capacitor shall be disregarded in determining the motor circuit conductor rating in accordance with Sec. 4.30.2.2.
Sec 4.60.1.9 p665
Rating or Setting of Motor Overload Device. Sec. 4.60.1.9 Capacitors with Motors. Ex.: A motor with 70% pf has a full load current rating of 143 A. Normally, the OL relay would be set for say, 125% of 143 or 179 A. But , because a PF capacitor is installed at the motor, the OL relay no longer will have 143 A flowing through it at full load. If the capacitor corrects to 100% PF, the effect will be as follows:
p3.27
Rating or Setting of Motor Overload Device. Sec. 4.60.1.9 Capacitors with Motors. Total *A Motor Current
B Working current from supply Controller
Motor
C Reactive or magnetizing Overload units should be set for current from PF 125% of current produce by Capacitor capacitor improved power factor instead of motor full-load current.
p3.27
*A (total motor current) = Vector sum of B and C
Rating or Setting of Motor Overload Device. Sec. 4.60.1.9 Capacitors with Motors.
Cos θ = 0.70 Ix = Magnetizing current
Ixc
L
Ixc = Capacitor current
θ
Iw
Iw = Working current
E Working current = Total motor current x
= 143 x 0.70 = 100 Amps Ix
L
p3.27
That is the current that will be flowing through the OL relay at full-load. Theref I = 143 A The OL relay must be set at
Motor Capacitor Circuit Conductors Sec. 4.60.1.8(a) Capacitors with Motors. The ampacity of the capacitor circuit conductors shall not be less than 135% of the rated current of the capacitor. The ampacity of conductors that connect a capacitor to the terminals of a motor or to motor circuit conductors shall not be less than onethird the ampacity of the motor circuit conductors & in no case less than 135% of the rated current of the capacitor.
Sec 4.60.1.8(a) p664
Branch Circuit Overload Protection Sec. 4.30.3.3 Intermittent and Similar Duty.
A motor used for a condition of service that is inherently shor time, intermittent, periodic, or varying duty, as illustrated by Table 4.30.2.2(b), shall be permitted to be protected against overload by the branch circuit short circuit & ground fault protective device, provided the protective device rating or setting does not exceed that specified in Table 4.30.14.6.
Any motor application shall be considered to be for continuou duty unless the nature of the apparatus it drive is such that th motor cannot operate continuously with load under any condi of use.
Branch Circuit Overload Protection Sec. 4.30.3.4 Selection of Overload Relay.
Where the overload relay selected in accordance with Sec. 4.30.3.2(a)(1) and ( c )(1) is not sufficient to start the motor or carry the load, the next higher size overload relay shall be permitted to be used, provided the trip current of the overload relay does not exceed the following percentage of motor name full load current rating: Motors with a marked service factor not less than 1.15 140% o Motors with a marked temperature rise not over 40140% C All other motors 130%
Special Feature of Overload Relay Selection of Overload Relay.
An special feature of overload relay can ease the relay current setting which can be varied to match the requirements of the load. The changeover is effected by simply turning a dial to the new value required. The range of adjustment is approximately 100% - 125% - 150%.
Branch Circuit Overload Protection Sec. 4.30.3.4 Selection of Overload Relay.
If not shunted during the starting period of the motor as provided in Section 4.30.3.5, the overload device shall have sufficient time delay to permit the motor to start & accelerate its load.
FPN: A Class 20 or 30 overload relay will provide a longer mot acceleration time than a Class 10 or 20, respectively. Use of a higher class overload relay may preclude the need for selectio a higher trip current.
Thermal Overload Relays Long time operating type
- In the case of loads having large inertia moments such as blowers, winders or centrifuges the starting time will be extended. Quick operating type
- The windings of submersible pump and compressor motors normally have a smaller overload capacity than those of standard motors, since they are generally cooled by water an other medium being pump. Therefore, it will be needing faste response time from protective relays.
Basic Protection Schemes Motor Damage characteristic
Circuit breaker contactor
Range 1.05 - 1.20 In Characteristic of thermal relay (140% In)
t
Cable thermal-withstan limit Class 30
30 s 20 s 1 to 10 s
Class 20 Class 10
Thermal relay
motor
20 to 30 ms In
6In
I”
short-ckt current breaking capacity
Trip Class of Thermal, Time-delay Magnetic or Solid State Overload Relays Table I
Tripping time Tp in seconds under the conditions Trip class
specified in Table II, Column D
10 A
2
<
Tp
≤
10
10
4
<
Tp
≤
10
20
6
<
Tp
≤
20
30
9
<
Tp
≤
30
Overload Relay Performance Test current as % Maximum Trip Times of Overload Relay Rating Class 10 Class 15 Class 20
Class 30
100 %
----------- Ultimately* -------------------
200 %
----------- 8 Minutes -------------------
600 %
10 seconds 15 seconds 20 seconds 30 secon
* Experience indicates that 2 to 4 hrs. is generally sufficient to verify this value. Systems which have large masses may requir additional time.
Limits of Operation of Time-delay Overload Relays When Energized on All Poles Table II Type of overload relay
Multiple of current setting A
B
Thermal type not compensated for ambient air temp.
1.0 1.2
Thermal type compensated for ambient air temp.
1.051.2
C
D
1.5 7.2 variations and magnetic type
1.5 7.2 variations
Ref. ambient air temperature
+40oC
+20oC
Limits of Operation of Time-delay Overload Relays When Energized on All Poles The relays shall comply with the requirements of Table II when tested as follows:
a) with the overload relay or starter in its enclosure, if normally fitted, & at A times the current setting from the cold state, at value of reference ambient air temperature stated in Table II. However, when the overload relay terminals have reached the equilibrium at the test current in less than 2 hr., the test dura can be the time needed to reach such thermal equilibrium;
b) when the current is subsequently raised to B times the curre setting, tripping shall occur in less than 2 Hr;
Limits of Operation of Time-delay Overload Relays When Energized on All Poles The relays shall comply with the requirements of Table II when tested as follows:
c) for class 10A overload relays energized at C times the curren setting, tripping shall occur in less than 2 min. starting from thermal equilibrium at the current setting; d) for class 10, 20, & 30 overload relays energized at C times the current setting, tripping shall occur in less than 4, 8, or 12 min. respectively, starting from thermal equilibrium at the current setting;
e) at D times the current setting, tripping shall occur within the limits given in Table I for the appropriate trip class starting fr the cold state.
Motor-Compressor & Branch Circuit Overload Protection Sec. 4.40.6.2 Air-Conditioning/Refrigerating Equipment
(a) (1) Each motor-compressor shall be protected against overlo & failure to start by a separate overload relay that is responsive to motor compressor current. This device shal selected to trip at not more than 140% of the motorcompressor rated-load current.
(3) A fuse or inverse time circuit breaker responsive to motor current, which shall also be permitted to serve as the branchcircuit short circuit & ground fault protective device. This device shall be rated at not more than 125% of motor compressor rated load current.
Motor Controllers Sec. 4.30.7.2 Circuit breaker Motor Controller Overload Protection
Motor
Controller Design. (a) Starting and Stopping. Each controller shall be capable of starting and stopping the motor it controls and shall be capable of interrupting the locked-rotor current of the motor.
Motor Controllers Sec. 4.30.7.3 Ratings The controller shall have a rating as specified in (a) of this section, unless otherwise permitted in (b) or (c), or as specified in (d) of this section, under the conditions specified.
Motor Controllers Sec. 4.30.7.3 Ratings (a) General.
(1) Controllers, other than inverse time circuit breakers and molded case switches, shall have horsepower ratings at the application voltage not lower than the horsepower rating of th motor. A controller for use with a Design E motor rated more t 2 hp shall (1) be marked as rated for use with a Design E moto or (2) have a horsepower rating not less than 1.4 times the rat of a motor rated 3 through 100 hp, or not less than 1.3 times t rating of a motor rated over 100 hp.
Motor Controllers Sec. 4.30.7.3 Ratings
(b) Small Motors. Device as specified in Section 4.30.7.1(b) & (c) shall be permitted as controller. (c) Stationary Motors of 2 Horsepower or Less. For stationary motors rated at 2 hp or less & 300 volts or less, the controller be permitted to be either of the following:
(1) A general-use switch having an ampere rating not less than twice the full-load current rating of the motor
(2) On ac circuits, a general-use snap switch suitable only for u on ac (not general-use ac-dc snap switches) where the motor f load current rating is not more than 80% of the ampere rating switch.
Motor Controllers Sec. 4.30.7.3 Ratings (d) Torque Motors. For torque motors, the controller shall have a continuous-duty, full-load current rating not less than the nameplate current rating of the motor. For a motor controller rated in horsepower but not marked with the foregoing current rating, the equivalent current rating shall be determined from the horsepower rating by using Tables 4.30.14.1, 4.30.14.2, 4.30.14.3, or 4.30.14.4.
Magnetic Starter Specification Rating
N5
N6
N7
N8
200-240V
22
30
37
45
3-Phase 380-440V
45
55
75
90
AC-4
18.5
22
30
37
45
55
75
AC- 3 kW
3-Phase A
200-240V
380-440V 37
AC- 3
200-240V
93
125
152
180
3-Phase
380-440V
90
110
150
180
AC-4
200-240V
80
93
125
150
380-440V 80
90
110
150
150
200
260
3-Phase AC-1
200-440V
150
Utilization Categories of A.C. Motor Starters Utilization cat.
Typical application
AC-1
Non-inductive or slightly inductive loads, resistive furnaces.
AC-2
Slip-ring motors: starting, switching off
AC-3
Squirrel-cage motors: starting, switching off motor during running1)
AC-4 Squirrel-cage motors: Starting, plugging, inching 1) AC-3 category may be used for occasional inching (jogging) or plugging for limited time periods such as machine set-up; durin limited periods the number of such operations should not excee per min. or more than ten in a 10-min. period
Making & Breaking Capacities According to Utilization Category Utilization Make & break test conditions category Ic/Ie Ur/Ue Cos θ On-time(s) Off-time No. of oper. cycle AC-1 AC-2 AC-39) AC-49)
1.5 4.0 8.0 10.0
AC-39) AC-49)
10 12
1.05 1.05 1.05 1.05
0.80 0.65 1) 1) Making 1.05 1) 1.05 1)
0.05 6) 0.05 6) 0.05 6) 0.05 6) conditions 9) 0.05 10 0.05 10
50 50 50 50 50 50
1) Cos θ = 0.45 for Ie ≤ 100 A, 0.35 for Ie > 100 A. 6) These off-times shall be not greater than the values specified in TableVIIa.
Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 Branch Circuit Short Circuit & Ground Fault Protection
Motor Controller Overload Protection
Motor
Rating or Setting for Individual Motor Circuit. (a) General.The motor branch circuit short circuit & ground fault protective device shall comply with (b) and either (c) or (d), as applicable. (b) All Motors. The motor branch circuit short circuit & ground fault protective device shall be capable of carrying the starting current of the motor.
4.30.3.3
4.30.4.2
4.30.4.2
4.30.3.10
4.30.4.3
4.30.5.3
Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 Rating or Setting for Individual Motor Circuit. (c)(1) Rating or Setting. A protective device that has a rating or setting not exceeding the value calculated according to the value given in Table 4.30.14.6 shall be used. Type of Motor
% of Full-Load Current Nontime Dual Element Instantaneous Inverse Tim Delay Fuse Time Delay Fuse Trip Breaker Breaker
single phase motor AC polyphase motor other than wound rotor Squirrel cage other than design E Design E Synchronous Wound rotor
300
175
800
250
300 300 300 150
175 175 175 150
800 1100 800 800
250 250 250 150
Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c) Rating or Setting.
(1) A protective device that has a rating or setting not exceeding the value calculated to the values given in Table 4.30.14.6 shall be used.
Exception No. 1: Where the values for branch circuit short circuit & ground fault protective devices determined by Tabl 4.30.14.6 do not correspond to the standard sizes or rating o fuses, nonadjustable circuit breakers, thermal protective devices, or possible settings of adjustable circuit breakers, th next higher standard size, rating, or possible setting shall be permitted.
Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c)(1) Rating or Setting.
Exception No. 2: Where the rating specified in Table 4.30.14.6 modified by Exception No. 1, is not sufficient for the starting current of the motor:
(a) The rating of a nontime-delay fuse not exceeding 600 amperes or a time-delay Class CC fuse shall be permitted to b increased but shall in no case exceed 400% of the full-load current. (b) The rating of a time-delay (dual-element) fuse shall be permitted to be increased but shall in no case exceed 225% of th full-load current.
Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c)(1) Rating or Setting.
Exception No. 2: Where the rating specified in Table 4.30.14.6 modified by Exception No. 1, is not sufficient for the starting current of the motor: (c) The rating of an inverse time circuit breaker shall be permitted to be increased but shall in no case exceed 400% for full-load currents of 100 amperes or less or 300% for full-load currents greater than 100 amperes.
(d) The rating of a fuse of 601-6000 ampere classification shall be permitted to be increased but shall in no case exceed 300% o the full-load current.
Nonreversing Combination Magnetic Starters NEMA size Volt Max. Hp Cont. Amp. Motor FL Amp. CB Rating 0
3
18
9.6
20
208
1
7½
27
22.0
50
227
2
15
45
42.0
100
238
90
80.0
125
156
50
135
130
200
154
5
100
270
248
400
161
6
200
540
480
800
167
3
230-
4
240
30
Nonreversing Combination Mag-Break Magnetic Starters NEMA size Volt Max. Hp Cont. Amp. Motor FL Amp. CB Rating 0
3
18
9.6
15
156
1
7½
27
22.0
30
136
2
15
45
42.0
50
119
90
80.0
100
125
50
135
130
150
115
100
270
248
400
161
3
230-
4
240
5
30
Protection for Motor Branch Circuits, NEMA AB1 The circuit breaker which is selected shall have a rated continuous current of at least 115% of the full load current of the motor and shall have a calibration setting sufficiently high to permit the motor or motors to start under normal operating conditions.
Wye-Delta Motors
Advantage is that no resistors or transformers are present to produce heat. Disadvantage is that starting torque is low and there are no torque/voltage adjustments. FULL
600
600
FULL
500
500
400
400 300
300
200
200
100
100 TIME
TIME
Close Transition
Setting of Instantaneous Element When motor data are not available, it is usually assumed that the locked-rotor current is equal to six times the motor full-load current, and that the motor acceleration time is 10 seconds. Normally, it is recommended that the setting of the motor feeder instantaneous element be at least twice the lockedrotor current.
Example, if locked-rotor current is 450 A, the instantaneous elements of the 125 A MCCB should be set at 900 A, approximately 7.2 times the CB rating.
Assumed Max. Short Circuit Current Rating of Unmarked Components Component
Short circuit current, kA
Circuit breaker (including GFCI type)
5
Motor controller, rated in horsepower(kW) a. 0 - 50
(0 - 37.3)
5
b. 51 - 200
(38 - 149)
10
c. 201 - 400
(150 - 298)
18
d. 401 - 600
(299 - 447)
30
e. 601 - 900
(448 - 671)
42
f. 901 - 1500
(672 - 1193)
85
Coordination with Short-Circuit Protective Devices Table XI Value of the prospective test current according to the Ie Rated operational current Ie (AC-3) (A)
Prospective current “ r “ (kA)
0 < Ie
≤
16
1
16 < Ie
≤
63
3
63 < Ie
≤
125
5
125 < Ie
≤
315
10
315 < Ie
≤
630
18
630 < Ie
≤
1000
30
1000 < Ie
≤
1600
42
Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c) Rating or Setting.
(2) Where maximum branch-circuit short-circuit and ground-fault protective device ratings are shown in the manufacturer’s overload relay table for use with a motor controller or are otherwise marked on the equipment, they shall not be exceeded even if higher values are allowed as shown above.
Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c) Rating or Setting.
(3) An instantaneous trip circuit breaker shall be used only if adjustable and if part of a listed combination motor controller having coordinated motor overload and short-circuit and ground-fault protection in each conductor, and the setting is adjusted to no more than the value specified in Table 4.30.14.6
Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c)(3) Rating or Setting.
Exception No. 1: Where the setting specified in Table 4.30.14. not sufficient for the starting current of the motor, the setting o an instantaneous trip circuit breaker shall be permitted to be increased but shall in no case exceed 1300 % of the motor ful load current for other than Design E motors or Design B ener efficient motors and no more than 1700 % of full load motor current for Design E motors or Design B energy Efficient mot Trip settings above 800 % for other than Design E motors or Design B energy efficient motors shall be permitted where th need has been demonstrated by engineering evaluation. In su cases, it shall not be necessary to first apply an instantaneous trip circuit breaker at 800 % or 1100 %.
Example for Motor Branch Circuit Short Circuit & Ground Fault Protection
A 30 hp, 230-V, 3 phase squirrel-cage motor is marked with the code letter M, indicating that the motor has a locked-rotor curr of 10 to 11.19 kVA/hp. A full-voltage controller is also provided, with running overload protection in the controller to protect the motor within its heating-damage curve on overload. Select a cir breaker which will provide short-circuit protection & will qualify as the motor-circuit disconnect means. 1. The motor has a full-load current of 80 A.
2. A CB suitable for use as the disconnect must have a current rating of at least 115% of 80 A.
Example for Motor Branch Circuit Short Circuit & Ground Fault Protection
3. Based on Table, it permits the use of an inverse-time CB rate not more than 250% of the motor full-load current. 2.5 x 80 A 200 A, a 225 AF with 200 AT setting could be selected.
4. The starting current of the motor will be [(30 hp x 11.19 kVA/hp) / (230 V x 1.732)]= 843 A.
5. The instantaneous characteristic of a 200 AT inverse-time CB will be about 200 A x 10 = 2000 A. Such a CB will provide protection for ground and short circuit without interfering wi the motor running overload protection.
Branch-Circuit Short-circuit & Ground Fault Protection Sec. 4.40.3.2 Air-Conditioning/Refrigerating Equipment (a) Rating or Setting for Individual Motor-Compressor.
A protective device having a rating or setting not exceeding 175% of the motor-compressor rated load current or branch circuit selection current, whichever is greater, shall be perm provided that, where the protection specified is not sufficient starting current of the motor, the rating or setting shall be permitted to be increased, but shall not exceed 225% of the m rated load current of branch circuit selection current, whiche is greater.
Air Condition & Refrigeration Equipment Short Circuit & Ground Fault Protection 60 Hz Comp 24.0 FLA
1
PH
197 Min.V
88.0 LRA 1
40
Max. Fuse Size
30
Min Circuit Ampacity
230
Volts
40A Fuse
PH
Air Condition & Refrigeration Equipment Short Circuit & Ground Fault Protection What size of conductor and protection is required for 24 A motor compressor connected to 240 V circuit? Step 1. Branch Circuit Conductor 24 x 1.25 = 30 A, rated 30A at 75 C Step 2. Branch Circuit Protection o
24 x 1.75 = 42 A, what is the rating of protective devic
Next size down = 40 A since Sec. 4.40.3.2(a) does not indicate that the next higher standard rating may be used.
If the 40A protection device isn’t capable of carrying the starting current, then the protection device can be sized up to 225% of th equipment load current rating. 24 x 2.25 = 54 A.
Example Calculation for Sealed Hermetic Motor Compressor
Size the protective devices & cable for the circuit components of a sealed hermetic motor compressor with a nameplate current rati of 10 A.
1. The full-load current used for all calculation for a sealed her motor compressor is the current marked on the unit’s namep
2. For continuous operation, the branch circuit conductors mu at least equal to 125% of 10 A or 13 A.
3. Conductors for branch circuit must, therefore, be not smalle 2mm2 (Type TW or THW).
Example Calculation for Sealed Hermetic Motor Compressor
4. Running overload protection from overload relays in the sta must have a rating or setting not over 140% of full-load (nameplate) current rating. This calls for an overload relay s trip at 1.4 x 10 A, or 14 A.
5. The max. fuse rating for short circuit protection for a herme motor compressor is 175% of the motor nameplate full-load current rating, which is 1.75 x 10 A or 17.5 A. That would in the used of 20 A fuses.
Where Sec.4.40.3.2(a) does not indicate that the next higher standard sizes or ratings fuse may be used, but it does permit up to 225% of the motor current where needed for starting of the motor.
Disconnecting Means Section 4.30.10.2 (b)
Disconnecting means w/in sight from motor & driven machinery
Basic Rule Disconnect means
(a)
Controller
Individual disconnecting means shall be located in sight from each controller location.
This additional switch is not needed if disconnect ahead of starter is lock-open type. Disconnect means
Motor
Driven Machinery
Disconnecting Means Section 4.30.10.3 Disconnecting Means Branch Circuit Short Circuit & Ground Fault Protection
Motor Controller Overload Protection Motor
Operation.
The disconnecting means shall open all ungrounded supply conductors & shall be designed so that no pole can be operated independently. The disconnecting means shall be permitted in the same enclosure with the controller.
Disconnecting Means Section 4.30.10.10 Ampere Rating & Interrupting Capacity.
(a) General. The disconnecting means for motor circuits rated 600 volts, nominal, or less, shall have an ampere rating of a least 115% of the full-load current rating of the motor. (b) Torque Motors. Disconnecting means for torque motor shall have an ampere rating of at least 115% of the motor nameplate current.
(c) For Combination Loads. Where two or more motors are used together or where one or more motors are used in combination with other loads, such as resistance heaters, & where the combined load may be simultaneous on a single disconnecting means, the ampere & horsepower ratings of combined load shall be determined as follows:
Disconnecting Means Section 4.30.10.10 (c) For Combination Loads.
(1) The rating of the disconnecting means shall be determined f the sum of all currents, including resistance loads, at the full load condition & also at the locked-rotor condition.
The full load current equivalent to the hp rating of each moto shall be selected from Tables 4.30.14.1, 4.30.14.2, 4.30.14.3, 4.30.14.4.
The locked-rotor current equivalent to the hp rating of each motor shall be selected from Table 4.30.14.5(a) or 4.30.14.5( The locked-rotor currents shall be added to the rating in amperes of other loads to obtain an equivalent locked-rotor current for the combined loads.
Disconnecting Means Section 4.30.10.10 (c) For Combination Loads.
(2) The ampere rating of the disconnecting means shall not be less than 115 % of the sum of all currents at the full load condition determined in accordance with Sec. 4.30.10.10(c)(1).
Exception: A listed nonfused motor circuit switch having a horsepower rating equal to or greater than the equivalent horsepower of the combined loads, determined in accordanc with Sec.4.30.10.10(c)(1), shall be permitted to have an amp rating less than 115% of the sum of all currents at the full lo condition.
Table 4.30.14.5(b) Conversion Table of Polyphase Design BCD & E Max. Locked-Rotor Currents for Sel. of Disconnecting Means & Controller as Det. fr. Hp Rated Hp
Max. Motor Locked-Rotor Current in Amp. 3-Phase, Design B,C,D & 115 Volts B,C,D
208 Volts
230 Volts
E
B,C,D
E
B,C,D
E
460 Volts B,C,D
E
1/2
40
40
22.1
22.1
20
20
10
10
3/4
50
50
27.6
27.6
25
25
12.5
12.5
1
60
60
33
33
30
30
15
15
1-1/2
80
80
44
44
40
40
20
20
2
100
100
55
55
50
50
25
25
3
--
--
71
81
64
73
32
36.5
5
--
--
102
135
92
122
46
61
7-1/2
--
--
140
202
127
183
63.5
91.5
Example of Disconnect for Combination Load
Assume a load consists of one 5hp, one 3hp, and two 1/2hp motors, plus a 10 kw heater, all rated 240 V, 3 phase, 60 hz. All motors are design B motors. Determine the size of disconnect. Sol’n.: Calculation of equivalent Full Load Current Rating Motor & other load Table Current (A)
5 hp
4.30.14.4
15.2
3 hp
4.30.14.4
9.6
1/2 hp
4.30.14.4
2.2
1/2 hp
4.30.14.4
2.2
10 kw
(10 x 1000)/(240 x 1.732)
24.1
Example of Disconnect for Combination Load Calculation of equivalent Locked Rotor Current Rating:
Motor & other load
Table
Current (A)
5 hp
4.30.14.5(b)
92
3 hp
4.30.14.5(b)
64
1/2 hp
4.30.14.5(b)
20
1/2 hp
4.30.14.5(b)
20
10 kw
(10 x 1000)/(240 x 1.732) Total
24.1 220.1
Example of Disconnect for Combination Load Minimum ampere rating of Disconnect = 1.15 x 53.3 = 61.3 A
Using Table 4.30.14.5(b) to obtain equivalent hp = 15 hp ( locke rotor current 232 A which is more than 220.1 A, but Table 4.30. FLA = 42A is less than 53.3A.)
General purpose switch satisfies the minimum hp requirement b fail to satisfy the minimum current requirement of 61.3 A (53.3 Therefor, the next larger size disconnect switch must be used which is 20hp. 54 A (over 53.3 A), locked rotor 290 A
Based on Sec.4.30.10.10(c)(2) Exception: A listed non-fused motor circuit switch having a horsepower rating equal to or greater than the equivalent horsepower of the combined loads, determined in accordance with Section 4.30.10.10(C)(1), shall be permitted to have an ampere rating less than 115% of the sum of all currents at the f load condition.
Load Break Switch Disconnector Specification Thermal current Ith Rated operational current Ie 400 V AC
100 A
125A
160A
A/B
A/B
A/B
AC 21A / AC 21B
100 / 100 125 / 125 160 / 160
AC 22A / AC 22B
100 / 100 125 / 125 160 / 160
AC 23A / AC 23B
63 / 63
63 / 63
160 / 160
WITHSTAND (AC 23A) Mechanical (No. of operation) 20000
20000
10000
Electrical (No. of operation) 1500 / 300 1000 / 200 1000 / 200
Utilization Categories Nature of Utilization categories current Category A Category B AC-20A* Alternating Current
Typical applications
AC-20B*
-Connecting & disconnecting under no-load conditions
AC-21B
-Switching of resistive loads including moderate overloads
AC-22A
AC-22B
-Switching of mixed resistive & inductive loads, including moderate overloads
AC-23A
AC-23B
-Switching of motor loads or other highly inductive loads
AC-21A
Utilization Category The designation of utilization categories is completed by suffix or B according to whether the intended applications require frequent or infrequent operations. Utilization categories with suffix B are appropriate for devices which, due to design or application, are only intended for infrequent operation. This could apply, for example, to disconnectors normally only operated to provide isolation for maintenance work or switching devices where fuse-link blade forms the moving contact.
Verification of rated making & breaking capacities
Conditions for making & breaking corresponding to various utilization categor Utilization Rated oprn’l category
current
Making
Breaking
Number of
I/Ie U/Ue cos θ Ic/Ie Uf/Ue cos θ oprt’g cycle
AC-20A/B All Values AC-21A/B All Values
1.5
1.05
0.95
1.5
1.05
0.95
5
AC-22A/B All Values
3
1.05
0.65
3
1.05
0.65
5
1.05
0.45
8
1.05
0.45
5
1.05
0.35
8
1.05
0.35
3
AC-23A/B 0< Ie ≤100 A 100 A < Ie
10 10
Feeder Tap Conductors Sec. 4.30.2.8 Feeder Short Circuit & Ground Fault Protection
Branch Circuit Short Circuit & Ground Fault Protection
Motor Controller
Feeder tap Feeder Conductor conductors shall have an ampacity not less Feeder Tap than that required by Conductor Part 4.30.2, shall terminate in a branch circuit and, in addition, shall meet Branch one of the following Circuit requirements: Conductors
Feeder Tap Conductors Sec. 4.30.2.8 (1) Be enclosed by either an enclosed controller or by a raceway, be not more than 3000 mm in length, and, for field installation, be protected by an overcurrent device on line side of the tap conductor, the rating or setting of which shall not exceed 1000% of tap conductor capacity (2) Have an ampacity of at least one-third that of the feeder conductors, be suitably protected from physical damage or enclosed in a raceway, and be not more than 7600 mm in length (3) Have the same ampacity as the feeders conductors
Motor Circuit Conductors Sec. 4.30.2.4 Feeder Short Circuit & Ground Fault Protection Branch Circuit short Circuit & Ground Fault Protection Motor Controller
Motor
Feeder Conductor
Feeder Tap Conductor
Branch Circuit Conductors
Several Motors or a Motor(s) & Other Load(s)
Conductors supplying several motors, or a motor and other load, shall have an ampacity at least equal to the sum of the full-load current rating of all the motors, plus 25% of the highest rated motor in the group, plus the ampere rating of other loads .
Motor Feeder Short-Circuit & GroundFault Protection, Sec. 4.30.5.2 Rating or Setting - Motor Load.
(a) Specific Load. A feeder supplying a specific fixed motor load(s) & consisting of conductor sizes based on Sec. 4.30.2.4 shall be provided with protective device having a rating or setting not gr than the largest rating or setting of the branch-circuit short-circuit ground-fault protective device for any motor supplied by the fee [based on the maximum permitted value for the specific type of protective device shown in Table 4.30.14.6, or Sec. 4.40.3.2(a) f hermitic refrigerant motor-compressors], plus the sum of the ot motors of the group.
Example of Feeder Protection Feeder Short Circuit & Ground Fault Protection Branch Circuit short Circuit & Ground Fault Protection Motor Controller
Motor
Feeder Conductor Feeder Tap Conductor
What is the size of feeder protection (inverse time o CB with 75 C terminals) & conductor are required for the following two motors?
Motor 1 - 20hp, 460V, 27A Branch Circuit Conductors
Motor 2 - 10hp, 460V, 14A
Example of Feeder Protection Step 1. Feeder Conductor Size ( 27A x 1.25 ) + 14 A = 48 A Use 8 mm2 rated 50A at 75 C Step 2. Branch Circuit protective device o
20hp Motor = 27A x 2.5 = 68A, use next size up = 70A 10hp Motor = 14A x 2.5 = 35A Step 3. Size of Feeder Protection 70A + 14A = 84A
Next size down = 80A, The next size up protection rule for branch circuit Exception 1 does not apply to feeder protection device
Motor Feeder Short-Circuit & GroundFault Protection, Sec. 4.30.5.2 Rating or Setting - Motor Load. (b)Other Installations. Where feeder conductors have an ampacity greater than required by Section 4.30.2.4, the rating or setting of the feeder overcurrent protective device shall be permitted to be based on the ampacity of the feeder conductors.
Ex. On Motor Feeder Short-Circuit & Ground-Fault Protection Time delay fuse
Time delay fuse
Time delay fuse
Nontime delay fuse
5 Hp
10 Hp
25 Hp
25 Hp
18 A
32 A
78 A
78 A
3 phase, 200 V, 60 Hz., squirrel cage induction motors
Ex. On Motor Feeder Short-Circuit & Ground-Fault Protection
1) The feeder conductors must have a carrying capacity that i computed as follows: (1.25 x 78) +78 + 32 +18 = 225.5 A , used 125 mm2 THW 2) Branch circuit protection
2-1) Nontime delay fuse= 300% x 78 = 234 A, used 250 A fuse
2-2) Time delay fuse = 175% x 78 = 136.5 A , used 150 A fuse 2-3) Time delay fuse = 175% x 32 = 56 A, used 60 A fuse 2-4) Time delay fuse = 175% x 18 = 31.5 A, used 35 A fuse
Ex. On Motor Feeder Short-Circuit & Ground-Fault Protection 3) Feeder Protection
The maximum rating or setting for the overcurrent device protection must not be greater than the largest rating or setti branch circuit protective device plus the sum of the full-load currents of the other motors. 250 + 78 + 32 + 18 = 378 A
Used 350 A Fuse or Circuit Breaker
Motor Control Centers Section 4.30.8.3 Overcurrent Protection. Motor control centers shall be provided with overcurrent protection in accordance with Article 2.40 based on the rating of the common power bus. This protection shall be provided by (1) an overcurrent protective device located ahead of the motor control center or (2) a main overcurrent protective device located within the motor control center. p608
Series Ratings Sec.2.40.7.7
Series Ratings. Where a circuit breaker is used on a circuit having an available fault current higher than its marked interrupting rating by being connected on the load side of an acceptable overcurrent protective device having higher rating the following shall apply. (b) Motor Contribution. Series ratings shall not be used where:
(1) Motors are connected on the load side of higher rated overcurrent device and on the line side of the lower rated overcurrent device, and (2)The sum of the motor full load currents exceeds 1% of the interrupting rating of the lower rated circuit breaker.
Series Ratings Sec.2.40.7.7 Series combination: 22 kA interrupting rating
10kA
Fault
M
Motor Contribution
Thank You Very Much for Listening
