Load calculation, optional method.

Part IV.  Optional Feeder and Service Load Calculations

220.80 General.   Optional feeder and service load calculations shall be permitted in accordance with Part IV.

220.82 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 and 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 220.82(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 220.61.

(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 or 3 volt-amperes/ft2 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 210.11 (C) (1) and (C) (2).

(3)  The nameplate rating of the following:

1. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit
2. Ranges, wall-mounted ovens, counter-mounted cooking units.
3. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)
4. 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 for central electric space-heating systems.  If the heat pump compressor is prevented from operating at the same time as 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 the four separately controlled units.

(5)  40 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units.

(6)  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 220.82 (C).

220.83 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 220.83 (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 at                                                              100

 Remainder of load at                                                                40

Load calculations shall include the following:                                                       

(1)  General lighting and general-use receptacles at 33 volt-amperes/m2 or 3 volt-amperes/ft2 as determined by 220.12. 

(2)  1500 volt-amperes for each 2-wire, 20-ampere small-appliance branch circuit and each laundry branch circuit covered in 210.11 (C) (1) and (C) (2).

(3)  The nameplate rating of the following:

1. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit
2. Ranges, wall-mounted ovens, counter-mounted cooking units.
3. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)
4. 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                                                                                           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 load                                                                      100                      Remainder of all other loads                                                        40

Other loads shall include the following:

(1)  General lighting and general-use receptacles at 33 volt-amperes/m2 or 3 volt-amperes/ft2 as determined by 220.12. 

(2)  1500 volt-amperes for each 2-wire, 20-ampere small-appliance branch circuit and each laundry branch circuit covered in 210.11 (C) (1) and (C) (2).

(3)  The nameplate rating of the following:

5. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit
6. Ranges, wall-mounted ovens, counter-mounted cooking units.
7. Clothes dryers that are not connected to the laundry branch circuit specified in item (2)
8. Water heaters