Philippine Electrical Code Part 1/Chapter 2. Wiring and Protection/Article 2.20 - Branch-Circuit, Feeder, And Service Calculations

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Article 2.20 - Branch-Circuit, Feeder, And Service Calculations

DISCLAIMER
This is not an official copy of the Philippine Electrical Code. This is a Design Guide according to the provisions of the Philippine Electrical Code. It also provides interpretation and annotations of the clauses of the Philippine Electrical Code. Any information, interpretation and/or annotation presented herein are based on personal opinion of the authors and does not represent the official interpretation of the Philippine Electrical Code.


While the authors have used good faith and efforts to ensure that the information and instructions contained in this work are accurate, the authors disclaim all responsibility for errors or omissions, including without limitation responsibility for damages resulting from the use of or reliance on this work. Use of the information and instructions contained in this work is at your own risk. If any contents or other technology this work contains or describes is subject to open source licenses or the intellectual property rights of others, it is your responsibility to ensure that your use thereof complies with such licenses and/or rights

Note: This is a work in progress...

Contents

2.20.1 General

2.20.1.1 Scope.

This article provides requirements for calculating branch-circuit, feeder, and service loads. Part 2.20.1 provides for general requirements for calculation methods. Part 2.20.2 provides calculation methods for branch circuit loads. Parts 2.20.3 and 2.20.4 provide calculation methods for feeders and services. Part 2.20.5 provides calculation methods for farms.

FPN: See Figure 2.20.1.1 for information on the organization of Article 2.20.

2.20.1.3 Application of Other Articles.

In other articles applying to the calculation of loads in specialized applications, there are requirements provided in Table 2.20.1.3 that are in addition to, or modifications of, those within this article.


Figure 2.20.1.1 Branch-Circuit, Feeder, and Service Calculation Methods



Table 2.20.1.3 Additional Load Calculation References
Calculation Article Section (or Part)
Air-Conditioning and Refrigerating Equipment, Branch-Circuit Conductor Sizing 4.40 Part 4.40.4
Cranes and Hoists, Rating and Size of Conductors 6.10 6.10.2.4
Electric Welders, ampacity calculations 6.30 6.30.2.1, 6.30.3.1
Electrically Driven or Controlled Irrigation Machines 6.75 6.75.1.7(a), 6.75.2.2(a)
 
Electrolytic Cell Lines 6.68 6.68.13(c)
Electroplating, Branch-Circuit Conductor Sizing 6.69 6.69.1.5
Elevator Feeder Demand Factors 6.20 6.20.2.4
Fire Pumps, Voltage Drop (mandatory calculation) 6.95 6.95.1.7
 
Fixed Electric Heating Equipment for Pipelines and Vessels, Branch-Circuit Sizing 4.27 4.27.1.4
Fixed Electric Space Heating Equipment, Branch-Circuit Sizing 4.24 4.24.1.3
Fixed Outdoor Electric Deicing and Snow-Melting Equipment, Branch-Circuit Sizing 4.26 4.26.1.4
 
Industrial Machinery, Supply Conductor Sizing 6.70 6.70.1.4(a)
Marinas and Boatyards, Feeder and Service Load Calculations 5.55 5.55.1.12
Mobile Homes, Manufactured Homes, and Mobile Home Parks, Total Load for Determining Power Supply 5.50 5.50.2.9(b)
Mobile Homes, Manufactured Homes, and Mobile Home Parks, Allowable Demand Factors for Park Electrical Wiring Systems 5.50 5.50.3.2
Motion Picture and Television Studios and Similar Locations – Sizing of Feeder Conductors for Television Studio Sets 5.30 5.30.2.9
 
Motors, Feeder Demand Factor 4.30 4.30.2.26
Motors, Multimotor and Combination-Load Equipment 4.30 4.30.2.25
Motors, Several Motors or a Motor(s) and Other Load(s)] 4.30 4.30.2.24
Over 600 Volt Branch Circuit Calculations 2.10 2.10.2.1(b)
Over 600 Volt Feeder Calculations 2.15 2.15.1.2(b)
 
Phase Converters, Conductors 4.55 4.55.1.6
Recreational Vehicle Parks, Basis of Calculations 5.51 5.51.6.3(a)
Sensitive Electrical Equipment, Voltage Drop (mandatory calculation) 6.47 6.47.1.4(d)
Solar Photovoltaic Systems, Circuit Sizing and Current 6.90 6.90.2.2
Storage-Type Water Heaters 4.22 4.22.2.2(e)
Theaters, Stage Switchboard Feeders 5.20 5.20.2.7

2.20.1.5 Calculations.

(a) Voltages. Unless other voltages are specified, for purposes of calculating branch-circuit and feeder loads, nominal system voltages of 115, 115/230, 208Y/120, 230, 347, 400Y/230, 460Y/265, 460, 600Y/347, and 600 volts shall be used.

(b) Fractions of an Ampere. Where calculations result in a fraction of an ampere that is less than 0.5, such fractions shall be permitted to be dropped.

2.20.2 Branch Circuit Load Calculations

2.20.2.1 General.

Branch-circuit loads shall be calculated as shown in 2.20.2.3, 2.20.2.5, and 2.20.2.7.

2.20.2.3 Lighting Load for Specified Occupancies.

A unit load of not less than that specified in Table 2.20.2.3 for occupancies specified therein shall constitute the minimum lighting load. 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.

FPN: The unit values herein are based on minimum load conditions and 100 percent power factor and may not provide sufficient capacity for the installation contemplated.

2.20.2.5 Other Loads — All Occupancies.

In all occupancies, the minimum load for each outlet for general-use receptacles and outlets not used for general illumination shall not be less than that calculated in 2.20.2.5(a) through (l), the loads shown being based on nominal branch-circuit voltages.

Exception: The loads of outlets serving switchboards and switching frames in telephone exchanges shall be waived from the calculations.

(a) Specific Appliances or Loads.

An outlet for a specific appliance or other load not covered in 2.20.2.5(b) through :(l) shall be calculated based on the ampere rating of the appliance or load served.

Table 2.20.2.3 General Lighting Loads by Occupancy
Type of Occupancy Unit Load
Volt-Amperes per Square Meter
Armories and auditoriums 11
Banks 39b
Barber shops and beauty parlors 33
Churches 11
Clubs 22
Court rooms 22
Dwelling unitsa 33
Garages — commercial (storage) 6
Hospitals 22
Hotels and motels, including apartment houses without provision for cooking by tenantsa 22
Industrial commercial (loft) buildings 22
Lodge rooms 17
Office buildings 39b
Restaurants 22
Schools 33
Stores 33
Warehouses (storage) 3
In any of the preceding occupancies except one-family dwellings and individual dwelling units of two-family and multifamily dwellings:  
Assembly halls and auditoriums 11
Halls, corridors, closets, stairways 6
Storage spaces 3
a See 2.20.2.5(j).

b See 2.20.2.5(k).


(b) Electric Dryers and Household Electric Cooking Appliances.

Load calculations shall be permitted as specified in 2.20.3.15 for electric dryers and in 2.20.3.16 for electric ranges and other cooking appliances.

(c) Motor Loads.

Outlets for motor loads shall be calculated in accordance with the requirements in 4.30.2.2, 4.30.2.4, and 4.40.1.6.

(d) Luminaires (Lighting Fixtures).

An outlet supplying luminaire(s) [lighting fixture(s)] shall be calculated based on the maximum volt-ampere rating of the equipment and lamps for which the luminaire(s) [fixture(s)] is rated.

(e) Heavy-Duty Lampholders.

Outlets for heavy-duty lampholders shall be calculated at a minimum of 600 volt-amperes.

(f) Sign and Outline Lighting.

Sign and outline lighting outlets shall be calculated at a minimum of 1200 volt-amperes for each required branch circuit specified in Section 6.0.1.5(a).

(g) Show Windows.

Show windows shall be calculated in accordance with either of the following:

(1) The unit load per outlet as required in other provisions of this section
(2) At 200 volt-amperes per 300 mm of show window
(h) Fixed Multioutlet Assemblies.

Fixed multioutlet assemblies used in other than dwelling units or the guest rooms or guest suites of hotels or motels shall be calculated in accordance with (h)(1) or (h)(2). For the purposes of this section, the calculation shall be permitted to be based on the portion that contains receptacle outlets.

(1) Where appliances are unlikely to be used simultaneously, each 1 500 mm or fraction thereof of each separate and continuous length shall be considered as one outlet of not less than 180 volt-amperes.
(2) Where appliances are likely to be used simultaneously, each 300 mm or fraction thereof shall be considered as an outlet of not less than 180 volt-amperes.
(i) Receptacle Outlets.

Except as covered in 2.20.2.5(j) and (k), receptacle outlets shall be calculated at not less than 180 volt-amperes for each single or for each multiple receptacle on one yoke. A single piece of equipment consisting of a multiple receptacle comprised of four or more receptacles shall be calculated at not less than 90 volt- amperes per receptacle. This provision shall not be applicable to the receptacle outlets specified in 2.10.1.11(c)(1) and (c)(2).

(j) Dwelling Occupancies.

In one-family, two-family, and multifamily dwellings and in guest rooms or guest suites of hotels and motels, the outlets specified in (j)(1), (j)(2), and (j)(3) are included in the general lighting load calculations of 2.20.2.3. No additional load calculations shall be required for such outlets.

(1) All general-use receptacle outlets of 20-ampere rating or less, including receptacles connected to the circuits in 2.10.1.11(c)(3)
(2) The receptacle outlets specified in 2.10.3.3(e) and (g)
(3) The lighting outlets specified in 2.10.3.21(a) and (b)
(k) Banks and Office Buildings.

In banks or office buildings, the receptacle loads shall be calculated to be the larger of (1) or (2):

(1) The computed load from 2.20.2.5
(2) 11 volt-amperes/m2
(l) Other Outlets.

Other outlets not covered in 2.20.2.5(a) through (k) shall be calculated based on 180 volt-amperes per outlet.

2.20.2.7 Loads for Additions to Existing Installations.

(a) Dwelling Units.

Loads added to an existing dwelling unit(s) shall comply with the following as applicable:

(1) Loads for structural additions to an existing dwelling unit or for a previously unwired portion of an existing dwelling unit, either of which exceeds 46.5 m 2 (500 ft 2 ), shall be calculated in accordance with 2.20.2.3 and 2.20.2.5.
(2) Loads for new circuits or extended circuits in previously wired dwelling units shall be calculated in accordance with either 2.20.2.3 or 2.20.2.5, as applicable.
(b) Other Than Dwelling Units.

Loads for new circuits or extended circuits in other than dwelling units shall be calculated in accordance with either 2.20.2.3 or 2.20.2.5, as applicable.

2.20.2.9 Maximum Loads.

The total load shall not exceed the rating of the branch circuit, and it shall not exceed the maximum loads specified in 2.20.2.9(a) through (c) under the conditions specified therein.

(a) Motor-Operated and Combination Loads.

Where a circuit supplies only motor-operated loads, Article 4.30 shall apply. Where a circuit supplies only air-conditioning equipment, refrigerating equipment, or both, Article 4.40 shall apply. For circuits supplying loads consisting of motor-operated utilization equipment that is fastened in place and has a motor larger than hp in combination with other loads, the total calculated load shall be based on 125 percent of the largest motor load plus the sum of the other loads.

(b) Inductive Lighting Loads.

For circuits supplying lighting units that have ballasts, transformers, or autotransformers, the calculated load shall be based on the total ampere ratings of such units and not on the total watts of the lamps.

(c) Range Loads.

It shall be permissible to apply demand factors for range loads in accordance with Table 2.20.3.16, including Note 4.

2.20.3 Feeder and Service Load Calculations

2.20.3.1 General.

The calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted by Parts III or IV or required by Part V have been applied.

FPN: See Examples D1(a) through D10 in Appendix D. See 2.20.2.9(b) for the maximum load in amperes permitted for lighting units operating at less than 100 percent power factor.

2.20.3.3 General Lighting.

The demand factors specified in 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 circuits for general illumination.

2.20.3.4 Show-Window and Track Lighting.

(a) Show Windows.

For show-window lighting, a load of not less than 660 volt-amperes/linear meter shall be included for a show window, measured horizontally along its base.

FPN: See 2.20.2.5(g) for branch circuits supplying show windows.

Table 2.20.3.3 Lighting Load Demand Factors
Type of Occupancy Portion of Lighting Load to Which Demand Factor Applies (Volt-Amperes) Demand Factor (Percent)
Dwelling units First 3000 or less at 100
From 3001 to 120,000 at 35
Remainder over 120,000 at 25
Hospitals* First 50,000 or less at 40
Remainder over 50,000 at 20
Hotels and motels, including apartment houses without provision for cooking by tenants* First 20,000 or less at 50
From 20,001 to 100,000 at 40
Remainder over 100,000 at 30
Warehouses (storage) First 12,500 or less at 100
Remainder over 12,500 at 50
All others Total volt-amperes 100
*The demand factors of this table shall not apply to the calculated load of feeders or services supplying areas in hospitals, hotels, and motels where the entire lighting is likely to be used at one time, as in operating rooms, ballrooms, or dining rooms


(b) Track Lighting.

For track lighting in other than dwelling units or guest rooms or guest suites of hotels or motels, an additional load of 150 volt-amperes shall be included for every 600 mm of lighting track or fraction thereof. Where multicircuit track is installed, the load shall be considered to be divided equally between the track circuits.

2.20.3.5 Receptacle Loads - Other Than Dwelling Units.

Receptacle loads calculated in accordance with 2.20.2.5(h) and (i) shall be permitted to be made subject to the demand factors given in Table 2.20.3.3 or Table 2.20.3.5.

Table 2.20.3.5 Demand Factors for Non-dwelling Receptacle Loads
Portion of Receptacle Load to Which Demand Factor Applies (Volt-Amperes) Demand Factor(Percent)
First 10 kVA or less at 100
Remainder over 10 kVA at 50

2.20.3.11 Motors.

Motor loads shall be calculated in accordance with 4.30.2.4, 4.30.2.5, and 4.30.2.6 and with 4.40.1.6 for hermetic refrigerant motor compressors.

2.20.3.12 Fixed Electric Space Heating.

Fixed electric space heating loads shall be calculated at 100 percent of the total connected load. However, in no case shall a feeder or service load current rating be less than the rating of the largest branch circuit supplied.

Exception: Where reduced loading of the conductors results from units operating on duty-cycle, intermittently, or from all units not operating at the same time, the authority having jurisdiction may grant permission for feeder and service conductors to have an ampacity less than 100 percent, provided the conductors have an ampacity for the load so determined.

2.20.3.13 Small Appliance and Laundry Loads - Dwelling Unit.

(a) Small Appliance Circuit Load.

In each dwelling unit, the load shall be calculated at 1 500 volt-amperes for each 2-wire small- appliance branch circuit required by 2.10.1.11(c)(1). Where the load is subdivided through two or more feeders, the calculated load for each shall include not less than 1 500 volt-amperes for each 2-wire small- appliance branch circuit. 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.

Exception: The individual branch circuit permitted by 2.10.3.3(b)(1), Exception No. 2, shall be permitted to be excluded from the calculation required by 2.20.3.13.

(b) Laundry Circuit Load.

A load of not less than 1500 volt- amperes shall be included for each 2-wire laundry branch circuit installed as required by 2.10.1.11(c)(2). This load shall be permitted to be included with the general lighting load and subjected to the demand factors provided in Table 2.20.3.3.

2.20.3.14 Appliance Load - Dwelling Unit(s).

It shall be permissible to apply a demand factor of 75 percent to the nameplate rating load of four or more appliances fastened in place, other than electric ranges, clothes dryers, space-heating equipment, or air- conditioning equipment, that are served by the same feeder or service in a one-family, two-family, or multifamily dwelling.

2.20.3.15 Electric Clothes Dryers - Dwelling Unit(s).

The load for household electric clothes dryers in a dwelling unit(s) shall be either 5 000 watts (volt-amperes) or the nameplate rating, whichever is larger, for each dryer served. The use of the demand factors in Table 2.20.3.15 shall be permitted. Where two or more single-phase dryers are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases.

Table 2.20.3.15 Demand Factors for Household Electric Clothes Dryers
Number of Dryers Demand Factor (Percent)
1–4 100%
5 85%
6 75%
7 65%
8 60%
9 55%
10 50%
11 47%
12–22  % = 47 – (number of dryers - 11)
23 35%
24–42  % = 35 – [0.5 × (number of dryers - 23)]
43 and over 25%

2.20.3.16 Electric Ranges and Other Cooking Appliances — Dwelling Unit(s).

The load for household electric ranges, wall- mounted ovens, counter-mounted cooking units, and other household cooking appliances individually rated in excess of 1¾ kW shall be permitted to be calculated in accordance with Table 2.20.3.16. Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for loads calculated under this section.

Where two or more single-phase ranges are supplied by a 3-phase, 4- wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases.

FPN No. 1: See Example D8 in Appendix D.

FPN No. 2: See Table 2.20.3.17 for commercial cooking equipment.

FPN No. 3: See the examples in Appendix D.

Table 2.20.3.16 Demand Factors and Loads for Household Electric Ranges, Wall-Mounted Ovens, Counter-Mounted Cooking Units, and Other Household Cooking Appliances over 1¾ kW Rating (Column C to be used in all cases except as otherwise permitted in Note 3.)
Number ofAppliances Demand Factor (Percent) (See Notes) Column C
Maximum Demand (kW)
(See Notes)
(Not over 12 kW Rating)
Column A
(Less than 3½ kW Rating)
Column B
(3½ kW to 8¾ kW Rating)
1 80 80 8
2 75 65 11
3 70 55 14
4 66 50 17
5 62 45 20
6 59 43 21
7 56 40 22
8 53 36 23
9 51 35 24
10 49 34 25
11 47 32 26
12 45 32 27
13 43 32 28
14 41 32 29
15 40 32 30
16 39 28 31
17 38 28 32
18 37 28 33
19 36 28 34
20 35 28 35
21 34 26 36
22 33 26 37
23 32 26 38
24 31 26 39
25 30 26 40
26–30 30 24 15 kW + 1 kW for each range
31–40 30 22
41–50 30 20 25 kW + ¾ kW for each range
51–60 30 18
61 and over 30 16
1. Over 12 kW through 27 kW ranges all of same rating. For ranges individually rated more than 12 kW but not more than 27 kW, the maximum demand in Column C shall be increased 5 percent for each additional kilowatt of rating or major fraction thereof by which the rating of individual ranges exceeds 12 kW.


2. Over 8¾ kW through 27 kW ranges of unequal ratings. For ranges individually rated more than 8¾ kW and of different ratings, but none exceeding 27 kW, an average value of rating shall be calculated by adding together the ratings of all ranges to obtain the total connected load (using 12 kW for any range rated less than 12 kW) and dividing by the total number of ranges. Then the maximum demand in Column C shall be increased 5 percent for each kilowatt or major fraction thereof by which this average value exceeds 12 kW.

3. Over 1¾ kW through 8¾ kW. In lieu of the method provided in Column C, it shall be permissible to add the nameplate ratings of all household cooking appliances rated more than 1¾ kW but not more than 8¾ kW and multiply the sum by the demand factors specified in Column A or B for the given number of appliances. Where the rating of cooking appliances falls under both Column A and Column B, the demand factors for each column shall be applied to the appliances for that column, and the results added together.

4. Branch-Circuit Load. It shall be permissible to calculate the branch-circuit load for one range in accordance with Table 2.20.3.16. The branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance. The branch- circuit load for a counter-mounted cooking unit and not more than two wall-mounted ovens, all supplied from a single branch circuit and located in the same room, shall be calculated by adding the nameplate rating of the individual appliances and treating this total as equivalent to one range.

5. This table also applies to household cooking appliances rated over 1¾ kW and used in instructional programs.

2.20.3.17 Kitchen Equipment — Other Than Dwelling Unit(s).

It shall be permissible to calculate the load for commercial electric cooking equipment, dishwasher booster heaters, water heaters, and other kitchen equipment in accordance with Table 2.20.3.17. These demand factors shall be applied to all equipment that has either thermostatic control or intermittent use as kitchen equipment. These demand factors shall not apply to space-heating, ventilating, or air- conditioning equipment.

However, in no case shall the feeder or service calculated load be less than the sum of the largest two kitchen equipment loads.

Table 2.20.3.17 Demand Factors for Kitchen Equipment — Other Than Dwelling Unit(s)
Number of Units of Equipment Demand Factor (Percent)
1 100
2 100
3 90
4 80
5 70
6 and over 65


2.20.3.21 Noncoincident Loads.

Where it is unlikely that two or more noncoincident loads will be in use simultaneously, it shall be permissible to use only the largest load(s) that will be used at one time for calculating the total load of a feeder or service.

2.20.3.22 Feeder or Service Neutral Load.

(a) Basic Calculation.

The feeder or service neutral load shall be the maximum unbalance of the load determined by this article. The maximum unbalanced load shall be the maximum net calculated load between the neutral and any one ungrounded conductor.

Exception: For 3-wire, 2-phase or 5-wire, 2-phase systems, the maximum unbalanced load shall be the maximum net calculated load between the neutral and any one ungrounded conductor multiplied by 140 percent.

(b) Permitted Reductions.

A service or feeder supplying the following loads shall be permitted to have an additional demand factor of 70 percent applied to the amount in 2.20.3.22(b)(1) or portion of the amount in 2.20.3.22(b)(2) determined by the basic calculation:

(1) A feeder or service supplying household electric ranges, wall- mounted ovens, counter-mounted cooking units, and electric dryers, where the maximum unbalanced load has been determined in accordance with Table 2.20.3.16 for ranges and Table 2.20.3.15 for dryers
(2) That portion of the unbalanced load in excess of 200 amperes where the feeder or service is supplied from a 3-wire dc or single- phase ac system, or a 4-wire, 3-phase; 3-wire, 2-phase system, or a 5- wire, 2-phase system
(c) Prohibited Reductions.

There shall be no reduction of the neutral or grounded conductor capacity applied to the amount in 2.20.3.22(c)(1), or portion of the amount in (c)(2), from that determined by the basic calculation:

(1) Any portion of a 3-wire circuit consisting of 2-phase wires and the neutral of a 4-wire, 3-phase, wye-connected system
(2) That portion consisting of nonlinear loads supplied from a 4- wire, wye-connected, 3-phase system

FPN No. 1: See Examples D1(a), D1(b), D2(b), D4(a), and D5(a) in Appendix D.

FPN No. 2: A 3-phase, 4-wire, wye-connected power system used to supply power to nonlinear loads may necessitate that the power system design allow for the possibility of high harmonic neutral currents.

2.20.4 Optional Feeder and Service Load Calculations

2.20.4.1 General.

Optional feeder and service load calculations shall be permitted in accordance with Part 2.20.4.

2.20.4.3 Dwelling Unit.

(a) Feeder and Service Load.

This section applies to a dwelling unit having the total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater. It shall be permissible to calculate the feeder and service loads in accordance with this section instead of the method specified in Part 2.20.3. The calculated load shall be the result of adding the loads from 2.20.4.3(b) and (c). Feeder and service- entrance conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 2.20.3.22.

(b) General Loads.

The general calculated load shall be not less than 100 percent of the first 10 kVA plus 40 percent of the remainder of the following loads:

(1) 33 volt-amperes/m2 for general lighting and general-use receptacles. The floor area for each floor shall be calculated from the outside dimensions of the dwelling unit. The calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.
(2) 1500 volt-amperes for each 2-wire, 20-ampere small-appliance branch circuit and each laundry branch circuit specified in 2.20.3.13.
(3) The nameplate rating of all appliances that are fastened in place, permanently connected, or located to be on a specific circuit, ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and water heaters.
(4) The nameplate ampere or kVA rating of all motors and of all low-power-factor loads.
(c) Heating and Air-Conditioning Load.

The largest of the following six selections (load in kVA) shall be included:

(1) 100 percent of the nameplate rating(s) of the air conditioning and cooling.
(2) 100 percent of the nameplate rating(s) of the heating when a heat pump is used without any supplemental electric heating.
(3) 100 percent of the nameplate ratings of electric thermal storage and other heating systems where the usual load is expected to be continuous at the full nameplate value. Systems qualifying under this selection shall not be calculated under any other selection in 2.20.4.3(c).
(4) 100 percent of the nameplate rating(s) of the heat pump compressor and 65 percent of the supplemental electric heating for central electric space heating systems. If the heat pump compressor is prevented from operating at the same time as the supplementary heat, it does not need to be added to the supplementary heat for the total central space heating load.
(5) 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units.
(6) 40 percent of the nameplate rating(s) of electric space heating if four or more separately controlled units.

2.20.4.4 Existing Dwelling Unit.

This section shall be permitted to be used to determine if the existing service or feeder is of sufficient capacity to serve additional loads. Where the dwelling unit is served by a 120/240-volt or 208Y/120-volt, 3-wire service, it shall be permissible to calculate the total load in accordance with 2.20.4.4(a) or (b).

(a) Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is Not to Be Installed.

The following formula shall be used for existing and additional new loads.

Load (kVA) Percent of Load
First 8 kVA of load at 100
Remainder of load at 40


Load calculations shall include the following:

(1) General lighting and general-use receptacles at 33 volt- amperes/m 2 as determined by 2.20.2.3
(2) 1500 volt-amperes for each 2-wire, 20-ampere small- appliance branch circuit and each laundry branch circuit specified in 2.20.3.13
(3) Household range(s), wall-mounted oven(s), and counter- mounted cooking unit(s)
(4) All other appliances that are permanently connected, fastened in place, or connected to a dedicated circuit, at nameplate rating
(b) Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is to Be Installed.

The following formula shall be used for existing and additional new loads. The larger connected load of air-conditioning or space-heating, but not both, shall be used.

Load Percent of Load
Air-conditioning equipment 100
Central electric space heating 100
Less than four separately controlled space-heating units 100
First 8 kVA of all other loads 100
Remainder of all other loads 40

Other loads shall include the following:

(1) General lighting and general-use receptacles at 33 volt- amperes/m 2 as determined by 2.20.2.3
(2) 1 500 volt-amperes for each 2-wire, 20-ampere small- appliance branch circuit and each laundry branch circuit specified in 2.20.3.13
(3) Household range(s), wall-mounted oven(s), and counter- mounted cooking unit(s)
(4) All other appliances that are permanently connected, fastened in place, or connected to a dedicated circuit, including four or more separately controlled space-heating units, at nameplate rating

2.20.4.5 Multifamily Dwelling.

(a) Feeder or Service Load.

It shall be permissible to calculate the load of a feeder or service that supplies three or more dwelling units of a multifamily dwelling in accordance with Table 2.20.4.5 instead of Part 2.20.3 if all the following conditions are met:

(1) No dwelling unit is supplied by more than one feeder.
(2) Each dwelling unit is equipped with electric cooking equipment.

Exception: When the calculated load for multifamily dwellings without electric cooking in Part 2.20.3 exceeds that calculated under Part 2.20.4 for the identical load plus electric cooking (based on 8 kW per unit), the lesser of the two loads shall be permitted to be used.

(3) Each dwelling unit is equipped with either electric space heating or air conditioning, or both. Feeders and service conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 2.20.3.22.
(b) House Loads.

House loads shall be calculated in accordance with Part III of this article and shall be in addition to the dwelling unit loads calculated in accordance with Table 2.20.4.5.

Table 2.20.4.5 Optional Calculations — Demand Factors for Three or More Multifamily Dwelling Units
Number of Dwelling Units Demand Factor (Percent)
3–5 45
6–7 44
8–10 43
11 42
12–13 41
14–15 40
16–17 39
18–20 38
21 37
22–23 36
24–25 35
26–27 34
28–30 33
31 32
32–33 31
34–36 30
37–38 29
39–42 28
43–45 27
46–50 26
51–55 25
56–61 24
62 and over 23
(c) Connected Loads.

The calculated load to which the demand factors of Table 2.20.4.5 apply shall include the following:

(1) 33 volt-amperes/m2 for general lighting and general-use receptacles.
(2) 1 500 volt-amperes for each 2-wire, 20-ampere small- appliance branch circuit and each laundry branch circuit specified in 2.20.3.13.
(3) The nameplate rating of all appliances that are fastened in place, permanently connected or located to be on a specific circuit, ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, water heaters, and space heaters. If water heater elements are interlocked so that all elements cannot be used at the same time, the maximum possible load shall be considered the nameplate load.
(4) The nameplate ampere or kilovolt-ampere rating of all motors and of all low-power-factor loads.
(5) The larger of the air-conditioning load or the space-heating load.

2.20.4.6 Two Dwelling Units.

Where two dwelling units are supplied by a single feeder and the calculated load under Part 2.20.3 exceeds that for three identical units calculated under 2.20.4.5, the lesser of the two loads shall be permitted to be used.

2.20.4.7 Schools.

The calculation of a feeder or service load for schools shall be permitted in accordance with Table 2.20.4.7 in lieu of Part III of this article where equipped with electric space heating, air conditioning, or both. The connected load to which the demand factors of Table 2.20.4.7 apply shall include all of the interior and exterior lighting, power, water heating, cooking, other loads, and the larger of the air-conditioning load or space-heating load within the building or structure.

Feeders and service-entrance conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 2.20.3.22. Where the building or structure load is calculated by this optional method, feeders within the building or structure shall have ampacity as permitted in Part 2.20.3 of this article; however, the ampacity of an individual feeder shall not be required to be larger than the ampacity for the entire building. This section shall not apply to portable classroom buildings.


Table 2.20.4.7 Optional Method — Demand Factors for Feeders and Service-Entrance Conductors for Schools
Connected Load Demand Factor (Percent)
First 33 VA/m2 Plus, (3 VA/ft2) at 100
Over 33 to 220 VA/m2 Plus, (3 to 20 VA/ft2) at 75
Remainder over 220VA/m2 (20 VA/ft2) at 25

2.20.4.8 Determining Existing Loads.

The calculation of a feeder or service load for existing installations shall be permitted to use actual maximum demand to determine the existing load under all of the following conditions:

(1) The maximum demand data is available for a 1-year period. Exception: If the maximum demand data for a 1-year period is not available, the calculated load shall be permitted to be based on the maximum demand (measure of average power demand over a 15- minute period) continuously recorded over a minimum 30-day period using a recording ammeter or power meter connected to the highest loaded phase of the feeder or service, based on the initial loading at the start of the recording. The recording shall reflect the maximum demand of the feeder or service by being taken when the building or space is occupied and shall include by measurement or calculation the larger of the heating or cooling equipment load, and other loads that may be periodic in nature due to seasonal or similar conditions.
(2) The maximum demand at 125 percent plus the new load does not exceed the ampacity of the feeder or rating of the service.
(3) The feeder has overcurrent protection in accordance with 2.40.1.4, and the service has overload protection in accordance with 2.30.7.1.

2.20.4.9 New Restaurants.

Calculation of a service or feeder load, where the feeder serves the total load, for a new restaurant shall be permitted in accordance with Table 2.20.4.9 in lieu of Part 2.20.3. The overload protection of the service conductors shall be in accordance with 2.30.7.1 and 2.40.1.4.

Feeder conductors shall not be required to be of greater ampacity than the service conductors.

Service or feeder conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 2.20.3.22.

Table 2.20.4.9 Optional Method — Permitted Load Calculations for Service and Feeder Conductors for New Restaurants
Total Connected Load (kVA) All Electric Restaurant Calculated Loads (kVA) Not All Electric Restaurant Calculated Loads (kVA)
0–200 80% 100%
201–325 10% (amount over 200) + 160 50% (amount over 200) + 200
326–800 50% (amount over 325) + 172.5 45% (amount over 325) + 262.5
Over 800 50% (amount over 800) +410 20% (amount over 800) + 476.3
Note: Add all electrical loads, including both heating and cooling loads, to calculate the total connected load. Select the one demand factor that applies from the table, then multiply the total connected load by this single demand factor.

2.20.5 Farm Load Calculation

2.20.5.1 General.

Farm loads shall be calculated in accordance with Part 2.20.5.

2.20.5.3 Farm Loads — Buildings and Other Loads.

(a) Dwelling Unit.

The feeder or service load of a farm dwelling unit shall be calculated in accordance with the provisions for dwellings in Parts 2.20.3 or 2.20.4. Where the dwelling has electric heat and the farm has electric grain-drying systems, Part 2.20.4 shall not be used to calculate the dwelling load where the dwelling and farm load are supplied by a common service.

(b) Other Than Dwelling Unit.

Where a feeder or service supplies a farm building or other load having two or more separate branch circuits, the load for feeders, service conductors, and service equipment shall be calculated in accordance with demand factors not less than indicated in Table 2.20.5.3.


Table 2.20.5.3 Method for Calculating Farm Loads for Other Than Dwelling Unit
Ampere Load at 240 Volts Maximum Demand Factor (Percent)
Loads expected to operate simultaneously, but not less than 125 percent full-load current of the largest motor and not less than the first 60 amperes of load 100
Next 60 amperes of all other loads 50
Remainder of other load 25

Other Pages in this Category: Chapter 2. Wiring and Protection

References