BRANCH-CIRCUIT, FEEDER, AND SERVICE CALCS 70-59

(FPN No. 1): See Examples 1(a), 1(b), 2(b), 4(a), and 5(a), Chapter 9. (FPN No. 2): A 3-phase, 4-wire power system used to supply power to computer systems or other similar electronic loads may necessitate that the power system design allow for the possibility of high harmonic neutral currents. C. Optional Calculations for Computing Feeder and Service Loads 220-30. Optional Calculation - Dwelling Unit. (a) Feeder and Service Load. For a dwelling unit having the total connected load served by a single 3-wire, 120/240-volt or 208Y/120-volt set of service-entrance or feeder conductors with an ampacity of 100 or greater, it shall be permissible to compute the feeder and service loads in accordance with Table 220-30 instead of the method specified in Part B of this article. Feeder and service-entrance conductors whose demand load is determined by this optional calculation shall be permitted to have the neutral load determined by Section 220-22. (b) Loads. The loads identified in Table 220-30 as "other load" and as "remainder of other load" shall include the following: (1) 1500 volt-amperes for each 2-wire, 20-ampere small appliance branch circuit and each laundry branch circuit specified in Section 220-16. (2) 3 volt-amperes per square foot (0.093 sq m) for general lighting and general-use receptacles. (3) The nameplate rating of all appliances that are fastened in place, permanently connected, or located to be on a specific circuit, ranges, wallheaters. mounted ovens, counter-mounted cooking units, clothes dryers, and water (4) The nameplate ampere or kVA rating of all motors and of all lowpower-factor loads. Table 220-30. Optional Calculation for Dwelling Unit Load in kVA Largest of the following five selections. (1) 100 percent of the nameplate rating(s) of the air conditioning and cooling, including heat pump compressors. (2) 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 figured under any other selection in this table. (3) 65 percent of the nameplate rating(s) of the central electric space heating, including integral supplemental heating in heat pumps. (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 of four or more separately controlled units. Plus: 100 percent of the first 10 kVA of all other load. 40 percent of the remainder of all other load. 70-60 NATIONAL ELECTRICAL CODE 220-31. Optional Calculation for Additional Loads in Existing Dwelling Unit. For an existing dwelling unit presently being served by an existing 120/240-volt or 208Y/120, 3-wire service, it shall be permissible to compute load calculations as follows: Load (in kVa) Percent of Load First 8 kVA of load at 100% Remainder of load at 40% Load calculation shall include lighting at 3 volt-amperes per square foot (0.093 sq m); 1500 volt-amperes for each 20-ampere appliance circuit; range or wall-mounted oven and counter-mounted cooking unit; and other appliances that are permanently connected or fastened in place, at nameplate rating. If air-conditioning equipment or electric space heating equipment is to be installed, the following formula shall be applied to determine if the existing service is of sufficient size. Air-conditioning equipment* 100% Central electric space heating* 100% Less than four separately controlled space heating units* 100% First 8 kVA of all other load 100% Remainder of all other load 40% Other loads shall include: 1500 volt-amperes for each 20-ampere appliance circuit. Lighting and portable appliances at 3 volt-amperes per square foot (0.093 sq m). Household range or wall-mounted oven and counter-mounted cooking unit. All other appliances fastened in place, including four or more separately controlled space heating units, at nameplate rating. *Use larger connected load of air conditioning and space heating, but not both. 220-32. Optional Calculation - Multifamily Dwelling. (a) Feeder or Service Load. It shall be permissible to compute the feeder or service load of a multifamily dwelling in accordance with Table 220-32 instead of Part B of this article where 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 computed load for multifamily dwellings without electric cooking in Part B of this article exceeds that computed under Part C 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.