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Section E3602 Service Size and Rating
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Ungrounded service conductors shall have an ampacity of not less than the load served. For one-family dwellings, the ampacity of the ungrounded conductors shall be not less than 100 amperes, 3 wire. For all other installations, the ampacity of the ungrounded conductors shall be not less than 60 amperes. [230.42(B), 230.79(C) & (D)]
The minimum load for ungrounded service conductors and service devices that serve 100 percent of the dwelling unit load shall be computed in accordance with Table E3602.2. Ungrounded service conductors and service devices that serve less than 100 percent of the dwelling unit load shall be computed as required for feeders in accordance with Chapter 37. [220.82(A)]
MINIMUM SERVICE LOAD CALCULATION [220.82(B) & (C)]
| LOADS AND PROCEDURE |
| 3 volt-amperes per square foot of floor area for general lighting and general use receptacle outlets. |
| Plus |
| 1,500 volt-amperes multiplied by total number of 20-ampere-rated small appliance and laundry circuits. |
| Plus |
| The nameplate volt-ampere rating of all fastened-in-place, permanently connected or dedicated circuit-supplied appliances such as ranges, ovens, cooking units, clothes dryers not connected to the laundry branch circuit and water heaters. |
| Apply the following demand factors to the above subtotal: |
| The minimum subtotal for the loads above shall be 100 percent of the first 10,000 volt-amperes of the sum of the above loads plus 40 percent of any portion of the sum that is in excess of 10,000 volt-amperes. |
| Plus the largest of the following: |
| One-hundred percent of the nameplate rating(s) of the air-conditioning and cooling equipment. |
| One hundred percent of the nameplate rating(s) of the heat pump where a heat pump is used without any supplemental electric heating. |
| One-hundred percent of the nameplate rating of the 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 figured under any other category in this table. |
| One-hundred percent of nameplate rating of the heat pump compressor and sixty-five percent of the supplemental electric heating load for central electric space-heating systems. If the heat pump compressor is prevented from operating at the same time as the supplementary heat, the compressor load does not need to be added to the supplementary heat load for the total central electric space-heating load. |
| Sixty-five percent of nameplate rating(s) of electric space-heating units if less than four separately controlled units. |
| Forty percent of nameplate rating(s) of electric space-heating units of four or more separately controlled units. |
| The minimum total load in amperes shall be the volt-ampere sum calculated above divided by 240 volts. |
Services that are not required to be 100 amperes shall be sized in accordance with Chapter 37. [230.42(A), (B), and (C)].
The combined rating of all individual service disconnects serving a single dwelling unit shall be not less than the load determined from Table E3602.2 and shall be not less than as specified in Section E3602.1. (230.79 & 230.80)
Systems shall be three-wire, 120/240-volt, single-phase with a grounded neutral. [220.82(A)]