Electrical Load Calculator

Because of Table 220.42, which discards 65 percent of the lighting and receptacle subtotal above the first 3,000 VA. A 2,400 square foot house starts with 7,200 VA of general lighting, 3,000 VA of small-appliance circuits and 1,500 VA of laundry — 11,700 VA — and the demand factors turn that into 6,045 VA before a single appliance has been added. The code is not being generous: it is recognizing that nobody has every receptacle in a house loaded at once, and the general lighting figure was never a measurement of anything in the first place. It is a per-square-foot allowance for a diversity of loads nobody can enumerate, so applying a diversity factor to it afterwards is consistent rather than a discount.

No. 220.12 computes the floor area from the outside dimensions of the dwelling and excludes open porches, garages, and unused or unfinished spaces not adaptable for future use. The trap is in that last clause: an unfinished basement with a stair, a floor and headroom is adaptable for future use and goes in, while a crawlspace you cannot stand in does not, and an unfinished attic with a permanent stair is a judgment call your inspector has already made a hundred times. This is also why the figure on a real estate listing is the wrong number to type — listings measure heated living area, which excludes the very basement the code wants included.

Because Table 220.55 Column C gives a demand of 8 kW for a single household range rated over 1¾ kW and up to 12 kW, regardless of where in that range the nameplate falls. A range has four or five heating elements and an oven, and they are thermostatically controlled and never all on at full output for long, so the code counts the demand rather than the connected load. Above 12 kW, Note 1 adds 5 percent to Column C for each additional kilowatt or major fraction of one — a 16 kW range comes to 8 kW plus 20 percent, or 9.6 kW. A cooktop and a wall oven fed by separate circuits are handled by other notes to the same table, which is a different calculation from the single-range case this page runs.

No — 220.60 says that where two loads are unlikely to be in use at the same time, only the larger goes into the total. Heating and cooling are the textbook case, and the worksheet shows both figures with the losing one struck out of the sum so a reviewer can see the choice was made rather than the smaller one forgotten. Two situations break the rule: a heat pump with electric supplementary heat runs the compressor and the strips simultaneously in defrost and at low outdoor temperatures, so those are one combined load and not two competing ones, and a house zoned so that one area is cooling while another is heating has coincident loads by design.

When there are four or more fastened-in-place appliances on the same service, and the count deliberately excludes the four that have their own articles — the electric range, the clothes dryer, the space heating and the air conditioning. Dishwasher, disposal, water heater, built-in microwave, trash compactor, attic fan and a whirlpool pump are the ones that usually make up the four. At three the whole group goes in at nameplate with no reduction at all, which means adding a fourth permanently connected appliance can lower the calculated service load rather than raise it — an outcome that looks wrong on a spreadsheet and is exactly what 220.53 says.

Either is permitted for a dwelling served at 120/240 V with a service of 100 A or larger, and the optional method usually gives the smaller answer. 220.82 takes the general loads — the same 3 VA per square foot, the same 1,500 VA circuits, plus the nameplate of every appliance — at 100 percent of the first 10 kVA and 40 percent of the remainder, then adds heating and cooling under its own selection rules. On an all-electric house with a large connected load the difference between the two methods can be a whole service size, which is why some jurisdictions ask to see the standard method even when the optional one governs. This page runs the standard method because it is the one that shows its work, article by article.

Usually not — the service neutral carries only the maximum unbalanced load, and 220.61 lets you compute it separately and smaller. A 240 V range, dryer or water heater puts nothing on the neutral except the 120 V portion of its own controls, so 220.61(B)(1) permits the range and dryer neutral loads to be taken at 70 percent of the figure used for the ungrounded conductors, and 220.61(B)(2) allows a further 70 percent on the part of the unbalanced load above 200 A. What it does not permit is shrinking the neutral below the grounding electrode conductor requirement, and a service with a large nonlinear load has a neutral question that 220.61 does not answer at all.