Shop Practice with Electrical Code: Electrical System Design (Residential) Jayson Bryan E. Mutuc, REE, RME BSEE-PUP MSEE, Major in Power Systems -MIT (candidate)
TOPICS • Service Entrance • Electric Meter • Plans and Specification • Design Analysis • Branch Circuit Load Calculation • Feeder and Service Load Calculation
SERVICE ENTRANCE •
• • •
It is described as the supply conductors which extends from the street main duct or transformer to the service or switchboard of the building supply. Most buildings service entrance are connected to the secondary line low voltage below 600 V. It can be 2, 3 or 4 wires including grounded neutral wire. Size of wires varies depending on demand load
SERVICE ENTRANCE
ELECTRIC METER • It is a device that measures the amount of electrical energy supplied to or produced by a residence, business or machine. • It is usually measured in kilowatt hours
1.3.2.1 Plan Requirements (p.28) (a) (b) (c) (d)
Location and Site Plan Legend or Symbol General Notes and/or Specification Electrical Layout (a) Plan for Power (b) Plan for Lighting and Receptacle Outlets (e) Schedule of Loads (f) Design Analysis (g) One Line Diagram (1) Lighting and Receptacle Outlet Load (2) Motor Loads (3) Feeders (4) Load Center (h) Title Block
Plans and Specification (c) General Notes and/or Specification. General Notes and Specifications, written on the plans or submitted on separate standard size sheets shall show: (1) Nature of Electrical Service, including number of phases, number of wires, voltage and frequency; (2) Type of Wiring; a. Service entrance b. Feeders, sub-feeder and branch circuit for lighting and/or power load (4) System or method of grounding
General Notes 1.
All electrical works indicated herein shall be done in accordance with the latest edition of Philippine Electrical Code Part 1, the requirements of the local building official and the electric utility serving the area. 2. The electrical supply/service voltage is 230V, single phase, two wires, grounded, 60 Hz. 3. Contractor shall verify and orient the actual locations of concrete terminal. 4. All installation shall be concealed from view, wiring shall be incased in PVC pipe or flexible conduit except power service which shall be in RSC. 5. The minimum size of wire shall be 2-3.5mm2 and 15mmø conduit. 6. All materials shall be new and approved type. Appropriate for both location and intended use. 7. Electrical installation shall be under a direct supervision of duly licensed electrical engineer or registered master electrician. 8. No revision in the design shall be done without the prior knowledge and approval of the designer and the owner. 9. Ground resistance shall not exceed 25 ohms. 10. Mounting heights for switches and convenience outlet shall be in 1.37m and 0.30m respectively, unless otherwise indicated in architectural plans.
Plans and Specification Legend - Electrical Symbols Schedule of Loads - tabulated information of electrical loads, size of wire and conduit per circuit up to service. Lighting System Layout - shows the lighting fixture and switches location and its wiring system. Power Layout - shows the location of convenience outlets, special outlets (acu, range, water pump, water heater, etc.), panel board, meter, service head, and their wiring system
Design Analysis Design Analysis shall be included on the drawings or shall be submitted on separate sheets of standard size, and shall show: (1) Branch Circuit, sub-feeders, feeders, busways, and service entrance (2) Types ratings, and trip settings of overload protective device (3) Calculation of short circuit current for determining the interrupting capacity of overcurrent protection device for residential, commercial, and industrial establishment (4) Calculation of voltage drops
Branch Circuit Load Calculation • Lighting Branch Circuit • Small Appliance Branch Circuit • Laundry Branch Circuit • Individual Branch Circuit (ACU, WH, WP, etc)
Article 2.10 (p.66) – Branch Circuits 2.10.1.3 Rating. Branch Circuits recognized by this article shall be rated in accordance with the maximum permitted ampere rating or setting of the overcurrent device.
Sizing of Conductors and Protective Devices 2.10.2. Branch Circuit Ratings (p.76) 2.10.2.1 (a)(1) Conductors – Minimum Ampacity and Size. General. Branch Circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and non continuous loads, the minimum branch circuit conductor size, before the application of any adjustment or correction factors, shall have an ampacity not less than the non continuous load plus 125 percent of the non continuous load. Note: same statement as in the Article 2.15 Section 1.2 p.91 For Feeders Minimum Rating and Size Continuous Load (Art 1.1 p.9) – A load where the maximum current is expected to continue for 3 hours or more
Sizing of Conductors and Protective Devices 2.10.2.2 Overcurrent Protection. Branch-circuit conductors and equipment shall be protected by overcurrent protective device that have a rating or setting not greater than the ampacity of the branch circuit conductors 2.10.2.2 (a) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination of continuous and non continuous loads, the rating of the overcurrent device shall not be less than the non continuous load plus 125 percent of the non continuous load. Note: same statement as in the Article 2.15 Section 1.3 p.93 For Feeders Overcurrent Protection
2.20.2 Branch Circuit Load Calculations Lighting Branch Circuit 2.10.2.5 (a)(p.81) A 15 or 20 – ampere branch circuits shall be permitted to supply lighting units or other utilization equipment, or a combination of both.
2.20.2.3 Lighting Load for Specified Occupancies (p.99). For dwelling units (Based on PEC 2009 Table 2.20.23 [p.100]) Total Lighting Load = Floor area (in sq.m) x 24 VA/sq.m or sometimes you can use the actual wattage rating of the lighting equipment The floor area for each floor shall be calculated from the outside dimensions of the building dwelling unit, or other area involved. For dwelling units, the calculated floor area shall not include open porches, garages or unused or unfinished spaces not adaptable for future use
Other Lighting Load Constants Type of Occupancy Armories, auditoriums, Churches, and Assembly Halls
Unit Load Volt-Ampere per Square Meter 8
Banks, Office Buildings
28
Barber Shops, Beauty Parlors, Dwelling Units, Schools, Stores
24
Type of Occupancy Clubs, Court rooms, Hotels, Motel Industrial Building, Hospitals, Restaurants
Unit Load Volt-Ampere per Square Meter 16
Garage – Commercial Halls, corridors, closet, Stairways
4
Ware house (storage)
2
2.10.1.11 (c)(1) Small-Appliance Branch Circuit (p.75) Also known as Convenience Outlet Branch Circuit. In addition to the number of branch circuits required, two or more additional 20 - ampere small appliance branch circuits shall be provided for all receptacle outlets 2.20.2.5 (i) Receptacle Outlets (p.101) receptacle outlets shall be calculated at not less than 180 volt-amperes for each single or for each multiple receptacle in one yoke. For four or more receptacle shall be calculated not less than 90 volt-ampere per receptacle.
Branch Circuit Rating: 1500 VA
2.10.1.11 (c)(2) Laundry Branch Circuit (p.75) In addition to the number of branch circuits required by other parts of this section, at least one or 20- ampere branch circuit shall be provided to supply the laundry receptacle outlet(s). This circuit shall have no other outlets. Branch Circuit Rating: 1500 VA
4.30.2 Motor Circuit Conductors (p.684) 4.30.2.2 (a) Single Motor (p.685). Conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motors full load current rating
4.30.4 Motor Branch-Circuit Short-Circuit and Ground Fault Protection (p.698) 4.30.4.2 Rating or Setting for Individual Motor Circuit. (b) The motor branch-circuit short-circuit and ground fault protective device shall be capable of carrying the starting current of the motor. (c) In Accordance with Table 4.30.4.2 A protective device that has a rating or setting not exceeding the value calculated according to the values given. In Table 4.30.4.2 shall be used Table 4.30.4.2 Maximum Rating or Setting of Motor BranchCircuit Short Circuit and Ground Fault Protective Device
Percentage of Full Load Current
Nontime Delay Fuse
Dual Element (TimeDelay) Fuse
Instanta neous Trip Breaker
Inverse time Breaker
300
175
800
250
Type of Motor Singlephase motors
2.20.3 Feeder and Service Load Calculations (p.103) 2.30.3.1 General. The calculated load of a feeder or service shall not be less than that the sum of the loads on the branch circuit supplied, after any applicable demand factors have been applied
2.20.3 Feeder and Service Load Calculations 2.20.3.3 General Lighting (p.103) The demand factors specified in the Table 2.20.3.3 shall apply to that portion of the total branch circuit load calculated for general illumination. They shall not be applied in determining the number of branch circuit for general illumination
Table 2.20.3.3 Lighting Load Demand Factors (p.104) Type of Occupancy Dwelling Units
Portion of Lighting load Which Demand Factor Applies (Volt-Amperes) First 3000 or less at From 3001 to 120,000 at Remainder over 120,000 at
Demand Factor (Percent) 100 35 25
2.20.3 Feeder and Service Load Calculations 2.20.3.13 Small-Appliance and Laundry Loads – Dwelling Unit (p.105) (a) Small Appliance Circuit Load. In each dwelling unit, the load shall be calculated at 1500 volt-amperes for each 2wire small appliance branch circuit required by 2.10.1.11 (c)(1) (b) Laundry Circuit Load. A load not less than 1500 voltamperes shall be included for each 2-wire laundry branch circuit installed as required by 2.10.1.11 (c)(2) These loads shall be permitted to be included with the general lighting load and subjected to the demand factors provided in Table 2.20.3.3
2.20.3 Feeder and Service Load Calculations 2.30.3.11 Motors (p.105) Motor loads shall be calculated in accordance with 4.30.24 4.30.2.4 Several Motor or a Motor(s) and Other Load(s)(p.687). Conductors supplying several motors, or a motor(s) and other load(s). Shall have an ampacity not less than 125 percent of the full-load current rating of the highest motor plus the sum of the full load current ratings of all the other motors in the group, plus the ampacity required for other loads. Feeder Conductor Size = [125% FLA of Highest Motor load]+ [Sum of other connected loads]
2.20.3 Feeder and Service Load Calculations 4.30.5.3 Rating or Setting – Power and Lighting Loads (p.706) Where a feeder supplies a motor load and in addition, a lighting or a lighting and appliance load, the feeder protective device shall have a rating sufficient to carry the lighting or lighting and appliance load plus the largest rating or setting of the branch-circuit short-circuit and ground fault protective device for any motor supplied by the feeder. Overcurrent Protective Device Rating = [OCP rating of Highest Motor load] + [Sum of the other connected loads]
Branch Circuit, Individual (Art 1.1) (p.7) A Branch Circuit that supplies only one utilization equipment (ACU, Range, Water Heater, Water Pump, etc.) Most Common Rating Range: 8000 W Water Heater: 5000 W For Motors (see table 4.30.14.2 (p.732)) 1 Hp at 230 V = 8 A 1 ½ Hp at 230 V = 10 A 2 Hp at 230 V = 12 A Range @ 8000 W computed @ 80% DF (see table 2.20.3.16(p.108)) ACU or motor load computed @ 100% DF
STANDARD RATING OF CIRCUIT BREAKERS AT (AMPERE TRIP)
AF (AMPERE FRAME)
15
50
20
50
30
50
40
50
50
50
60
100
70
100
80
100
90
100
100
100
110
225
125
225
150
225
175
225
Allowable Ampacities of Insulated Conductors Rated 0 Through 2000 Volts, 75°C Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth Size (mm2)
TYPE (THWN) Ampacity (A)
2.0
20
3.5
25
5.5
35
8.0
50
14
65
22
85
30
110
38
125
50
145
60
160
80
195
Some Conductor data's Trade Name
Type Letter
Maximum Operating Temperature
Application Provisions
Moisture – resistant Thermoplastic
TW
60°C
Dry and Wet Location
Moisture – and heat resistant thermoplastic
THW or THWN
75°C
Dry and Wet Location
Heat Resistant thermoplastic
THHN
90°C
Dry and Damp Location
Number of Conductors (THWN,THHN) in Rigid PVC Conduit Conductor Size (mm2)
Trade Size (mm)
15
20
25
32
40
50
65
2.0
9
17
28
51
70
118
170
3.5
6
12
20
37
51
86
124
5.5
4
7
13
23
32
54
78
8.0
2
4
7
13
18
31
45
14
1
3
5
9
13
22
32
22
1
1
3
6
8
14
20
30
1
1
2
4
6
10
14
38
0
1
1
3
4
7
10
50
0
1
1
2
3
6
9
60
0
1
1
1
3
5
7
80
0
1
1
1
2
4
6
2.50.6.13 Size of Equipment Grounding (Bonding) Conductor (p.240) 2.50.6.13 (f)(1) Based on Rating of Overcurrent Protective Device. Each parallel equipment grounding conductor shall be sized on the basis of the ampere rating of the overcurrent protecting the circuit conductors in the raceway or cable in accordance with Table 2.50.6.13
Table 2.50.6.13 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment (p.241) Minimum Size Equipment Grounding Conductors Rating or Setting of Overcurrent Device in Circuit
Conductor Size (mm2)
15
2.0
20
2.0
30
2.0
40
3.5
60
5.5
100
8.0
200
14
Sizing of Service Entrance Conductors Size of Service Entrance Conductors = sum of the computed load + 25% of the largest motor FLA Size of Service Equipment = largest motor protective device + sum of ampere rating of remaining branch circuit
Sample Computation Ex. Single Family Dwelling Unit The dwelling has a floor area of 145 m2. It has the typical household appliances including one 8-kW electric range, two 1-Hp room airconditioning unit, 1.5-Hp room air conditioning unit, and one 1-Hp water pump. Total Load a) General Lighting 145 m2 x 24 VA/ m2 = 3480 VA The computed load is 3480 VA/230 V =15 A One branch circuit of 20-ampere would be theoretically adequate, however for the flexibility and to allow future needs provide two 20 ampere branch circuits for lighting and convenience outlet.
b)
c)
Small Appliance Load One 20-ampere @ 1500 VA = 1500 VA Provide one 20-ampere small appliance circuit
Laundry Circuit One 20-ampere @ 1500 VA = 1500 VA Provide one 20-ampere laundry circuit Sub-Total = 6480 VA Application of Demand Factors First 3000 VA @ 100% DF = 3000 VA Remainder @ 35% DF (3480 x 0.35) = 1218 VA
Other Loads: One 8-kW electric range @ 80% = 6400 VA Provide one 40-ampere electric range circuit Two 1-Hp room acu, 8A x 230V x 2 @ 100% DF = 3680 VA Provide two 30-ampere room acu circuits One 1.5-Hp room acu, 10A x 230V @ 100% DF = 2300 VA Provide one 30-ampere room acu circuit One 1-Hp water pump, 8A x 230V @ 100% DF = 1840 VA Provide one 30-ampere water pump circuit Total Net Computed Load
= 18438 VA
Circuit Requirement: Use two 20-ampere 2-wire branch circuits, two 20-ampere 3-wire branch circuits, four 30-ampere 3-wire branch circuits, and one 40-ampere 3-wire branch circuit.
Service Entrance Conductors: Total Full Load Current: [18438 + 25%(2300)] / 230V = 83 Amperes Use 2-38mm2 + 1-8.0mm2 THWN wire
Service Equipment: Maximum Current Rating of Protective Device Inverse Time Circuit Breaker: [3000 VA + 1218 VA + 6400 VA + 3600 VA + 250%(2300 VA) + 1840 VA] / 230 V = 95 Amperes Service Equipment Rating: Use one 125 AT/225AF, 2P 240V molded case circuit breaker.
