PEC 2017 – Article 2.20

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Article 2.20 – BRANCH-CIRCUIT, FEEDER, AND SERVICE CALCULATIONS

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 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 feeder and service loads. Part 2.20.5 provides calculation methods for farm loads.

FPN No. 1: See examples in Appendix D.

FPN No. 2: See Figure 2.20.1.1 for information on the organization of Article 2.20.

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

2.20.1.3 Other Articles for Specific-Purpose Calculations.

Table 2.20.1.3 shall provide references for specific-purpose calculation requirements not located in Chapters 5, 6, or 7 that amend or supplement the requirements of this article.

Table 2.20.1.3 Specific-Purpose Calculation References

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, 380, 400Y/230, 460Y/265, 460, 660Y/380, and 660 volts shall be used.

(B) Fractions of an Ampere. Calculations shall be permitted to be rounded to the nearest whole ampere, with decimal fractions smaller than 0.5 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 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 are based on minimum load conditions and 100 percent power factor and may not provide sufficient capacity for the installation contemplated.

Exception No. 1: Where the building is designed and constructed to comply with an energy code adopted by the local authority the lighting load shall be permitted to be calculated at the values specified in the energy code where the following conditions are met.

(1) A power monitoring system is installed that will provide continuous information regarding the total general lighting load of the building

(2) The power monitoring system will be set with alarm values to alert the building owner or manager if the lighting load exceeds the values set by the energy code.

(3) The demand factors specified in 2.20.3.3 are not applied to the general lighting load.

Exception No. 2: Where a building is designed and constructed to comply with an energy code adopted by the local authority and specifying an overall lighting density of less than 13.5 volt-amperes/13.5 m², the unit lighting loads in Table 2.20.2.3 for office and bank areas within the building shall be permitted to be reduced by 11 volt-amperes/11 m².

Table 2.20.2.3 General Lighting Loads by Occupancy

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.

(B) Electric Dryers and Electric Cooking Appliances in Dwellings and Household Cooking Appliances Used in Instructional Programs. 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 Outlets. Loads for motor outlets shall be calculated in accordance with the requirements in 4.30.2.2, 4.30.2.4, and 4.40.1.6.

(D) Luminaires. An outlet supplying luminaire(s) shall be calculated based on the maximum volt-ampere rating of the equipment and lamps for which the luminaire(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 minimum of 1200 volt-amperes for each required branch circuit specified in 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 linear 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 1500 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(3) 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 calculated load from 2.20.2.5(I)

(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 m², 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 8 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 and LED Lighting Loads. For circuits supplying lighting units that have ballasts, transformers. autotransformers, or LED drivers, 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 2.20.2. after any applicable demand factors permitted by Part 2.20 3 or 2.20.4 or required by Part 2.20.5 have been applied

FPN: See Examples D1 to D10 in Appendix D. See 2.202.9(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.

Table 2.20.3.3 Lighting Load Demand Factors

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 2.20.25(G) for branch circuits supplying show windows.

(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

Exception: If the track lighting is supplied through a device that limits the current to the track, the load shall be permitted to be calculated based on the rating of the device used to limit the current.

2.20.3.5 Receptacle Loads Other Than Dwelling Units.

Receptacle loads calculated in accordance with 2.20.2.5(H) and (1) shall be permitted to be made subject to the demand factors given in Table 2.20.3.3 or Table 2.20.3.5.

Portion of Receptacle Load to Which Demand Factor Applies (Volt-Amperes)Demand Factor (%)
First 10 kVA or less at100
Remainder over 10 kVA at50
Table 2.20.3.5 Demand Factors for Non-Dwellings Receptacle Loads

2.20.3.11 Motors.

Motor loads shall be calculated in accordance with 4.30.2.4, 4.30.2.5, 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 can be supported by load computations, the feeder and service conductors are permitted 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 1500 volt-amperes for each 2-wire small-appliance branch circuit as covered 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 1500 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 covered 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 5000 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. Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for loads calculated in this section.

Table 2.20.3.15 Demand Factors for Household Electric Clothes Dryers

2.20.3.16 Electric Cooking Appliances in Dwelling Units and Household Cooking Appliances Used in Instructional Programs.

The load for household electric ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances individually rated in excess of 14 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 the examples in Appendix D.

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

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 1/4 kW Rating (Column C to be used in all cases except as otherwise permitted in Note 3.)

Notes:

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 834 kW through 27 kW ranges of unequal ratings. For ranges individually rated more than 8 3/4 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

3. Over 134 kW through 834 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 134 KW but not more than 834 kW and multiply the sum by the demand factors specified in Column A or Column 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 shall also apply to household cooking appliances rated over 13/4 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 Units

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 conductor 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 conductor and any multiplied by 140 percent. one ungrounded conductor

(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 following basic calculations:

(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 system; or a 3-wire, 2-phase system; or a 5-wire, 2-phase system

FPN: See Examples D6 to D8 in Appendix D

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 n (C)(2), from that determined by the basic calculation:

(1) Any portion of a 3-wire circuit consisting of 2 ungrounded conductors and the neutral conductor 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: A 3-phase, 4-wire, wye-connected power system used to supply power to nonlinear loads may necessitate that the power system design allows for the possibility of high harmonic neutral conductor currents.

2.20.3.23 Dwelling Unit-More than 150 Square Meters Floor Area.

 For a dwelling unit having a floor area more than 150 square meters, the feeder and service loads shall be computed with 100 percent demand factor on the air-conditioning load and the lighting load. The cooking load shall be computed in accordance with Section 2.20.3.16. Other load shall be permitted to be computed with 40 percent demand factor.

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 230-volt set of 2-wire service, or 115/230 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 III of this article. 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) 24 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 covered in 2.10.1.11(C)(1) and (C) (2).

(3) The nameplate rating of the following:

a. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit

b. Ranges, wall-mounted ovens, counter-mounted cooking units

c. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)

d. Water heaters

(4) The nameplate ampere or kVA rating of all permanently connected motors not included in item (3).

(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 heat pump when the heat pump is used without any supplemental electric heating.

(3) 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.

(4) 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units.

(5) 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 230-volt, 2-wire service, or 115/230-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 percentages shall be used for existing and additional new loads.

Load (kVA)Percent of Load
First 8 kVA of Load at100
Remainder of Load at40

Load calculations shall include the following:

(1) General lighting and general-use receptacles at 24 volt-amperes/m² 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 covered in 2.10.1.11(C)(1) and (C) (2)

(3) The nameplate rating of the following:

a. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit

b. Ranges, wall-mounted ovens, counter-mounted cooking units

c. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)

d. Water heaters

(B) Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is to Be Installed. The following percentages 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% of Load
Air-conditioning equipment100
Central electric space heating100
Less than four separately controlled space-heating units100
First 8 kVA of all other loads100
Remainder of all other loads40

(1) General lighting and general-use receptacles at 24 volt-amperes/m2 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 covered in 2.10.1.11(C)(1) and (C) (2)

(3) The nameplate rating of the following:

a. All appliances that are fastened in place. permanently connected, or located to be on a specific circuit

b. Ranges, wall-mounted ovens, counter-mounted cooking units

c. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)

d. Water heaters

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 2.20,3 of this article and shall be in addition to the dwelling unit loads calculated in accordance with Table 2.20.4.5.

(C) Calculated Loads. The calculated load to which the demand factors of Table 2.20.4.5 apply shall include the following:

(1) 24 volt-amperes/m² for general lighting and general-use receptacles

(2) 1500 volt-amperes for each 2-wire, 20-ampere small-appliance branch circuit and each laundry branch circuit covered in 2.10.1.11(C)(1) and (C)(2)

(3) The nameplate rating of the following:

a. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit

b. Ranges, wall-mounted ovens, counter-mounted cooking units

c. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)

d. Water heaters

(4) The nameplate ampere or kVA rating of all permanently connected motors not included in item (3)

(5) The larger of the air-conditioning load or the fixed electric 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 III of this article exceeds that for three identical units calculated under 2.20.4.5, the lesser of the two loads shall be permitted to be used.

Table 2.20.4.5 Optional Calculations – Demand Factors for Three or More Multifamily Dwelling Units

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 2.20.3 where equipped with electric space heating, air conditioning, or both. The connected load to which the demand factors of Table 220.86 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 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; 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.

Demand Factor (%)
100
75
25
Table 2.20.4.7 Optional Method – Demand Factors for Feeders and Service Conductors for Schools

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 (the highest average kilowatts reached and maintained for a 15-minute interval) 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

2.20.5 Farm Load Calculations

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 Part 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 of this article shall not be used to calculate the dwelling load where the dwelling and farm loads 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.

2.20.5.4 Farm Loads Total.

Where supplied by a common service, the total load of the farm for service conductors and service equipment shall be calculated in accordance with the farm dwelling unit load and demand factors specified in Table 2.20.5.4. Where there is equipment in two or more farm equipment buildings or for loads having the same function, such loads shall be calculated in accordance with Table 2.20.5.3 and shall be permitted to be combined as a single load in Table 2.20.5.3 for calculating the total load.

Ampere Load at 230 Volts MaximumDemand Factor (%)
Loads expected to operate simultaneously, but not less than 125% full-load current of the largest motor and not less than the first 60 A of load100
Next 60 A of all other loads50
Remainder of other load25
Table 2.20.5.3 Method for Calculating Farm Loads for Other Than Dwelling Unit
Demand Factor (%)
Largest Load100
Second Largest Load75
Third Largest Load65
Remaining Loads50
Table 2.20.5.4 Method for Calculating Total Farm Load

Note: To this total load, add the load of the farm dwelling unit calculated in accordance with Parts 2.20.3 or 2.20.4.