NEC Standard Method Single Family Residential - Electric Service Entrance Load Calculator

Enter plain numbers in cells without text or labels. If you leave any cells empty they will be calculated as zero.

Total Square feet of dwelling

Total # of Small Appliance Branch circuits (must be at least 2). If you have gas appliances which require a 120v branch circuit include them here.

Total # of Laundry Branch circuits (must be at least 1)

What's the Difference between Watts and Volt-Amps? Volt-amps as the name implies = volts * amps, but watts also = volts * amps, so what is the difference? Volt-amp ratings represent a maximum value, whereas Watt ratings are more like an average value over time. For some appliances both ratings have the same value, and for others there is a large difference. Imagine an oven that draws lots of current while it is preheating, but then may use very little for several minutes at a time once it is heated up. When there is a difference then volt-amps will be the larger of the two, and the ratio of watts/volt-amps is called the power factor, and is represented as either a decimal (0.8) or a percentage (80%). Confused? Don't sweat it, just use which ever value is on the appliance name plate or the larger of the two in the rare case that both might be listed.

Fastened in place Electrical appliances - Do not include gas appliances in this section. Use nameplate rating in volt-amps or watts - If appliance is rated in amps then volt-amps = amps * volts. Voltage value is either 120 or 240. So, for a 120 volt appliance which is rated at 15 amps, 120 volts * 15 amps = 1800 volt-amps.

Total # of water heaters

Volt-amp rating of water heater

Total # of trash compactors

Volt-amp rating of trash compactor

Total # of dishwashers

Volt-amp rating of dishwasher

Total # of disposals

Volt-amp rating of disposal

Total # of microwave ovens

Volt-amp rating of microwave oven

Total # of range hoods

Volt-amp rating of range hood

Other fastened in place appliances - use this section to define things like spas which aren't specified above.

Total # of other fastened in place appliance #1

Volt-amp rating of other fastened in place appliance #1

Total # of other fastened in place appliance #2

Volt-amp rating of other fastened in place appliance #2

Total # of other fastened in place appliance #3

Volt-amp rating of other fastened in place appliance #3

Total # of clothes dryers

Volt-amp rating of clothes dryer (must be at least 5000)

Total # of Ranges

Volt-amp rating of Range

Total # of Ovens - Note: If there is a range, and no additional oven then don't put anything here.

Volt-amp rating of Oven

Total # of Cooktops - Note: If there is a range, and no additional cooktop then don't put anything here.

Volt-amp rating of Cooktop

Total # of Other cooking appliance over 1750 volt-amps

Volt-amp rating of Other cooking appliance over 1750 volt-amps

Volt-amp rating of Larger of Heating OR Air conditioning system - always include air handler. For heat pump include compressor and the maximum amt of electrical heat that can be energized while compressor is running.

Volt-amp rating of Largest Single Motor (usally the HVAC compressor or air handler motor)

Service voltage is assumed to be 240

This is a simple free program for calculating electrical load for single family residential dwellings. This calculation determines the size of your electric service entrance (and meter) and main electrical panel based upon your potential load usage. If you are thinking about adding on or building a new house, then this calculator will help you to determine if your existing entrance is big enough or if you will have to spend a considerable amount to upgrade. Your local codes department will probably let you use a larger service entrance than the minimum if you want (up to a point), but you can't (and don't want to) have one that is even a little bit too small.

This program calculates total service load based upon the 2005 National Electrical Code Article 220. A balanced load is assumed.

Note: This program makes quick work of a lengthy calculation. In many cases you can use the values for volt-amp nameplate ratings that are provided and you will still get pretty good results (as an estimate only). Also this program does not have any provisions for usage allocation in the case of multiple major appliances circuits, so you will notice that if you input that the dwelling has more than one dryer circuit for example (maybe one in the basement and another in a main floor utility area) then it will show that you need to have a much bigger service entrance, but this isn't really correct in all cases because the code recognizes that you probably don't usually have a dryer plugged into both of them at the same time. If however, you have a second dryer outlet in an area of the house which might be used as a separate habitation the inspector will probably count the extra appliance circuit against the total load, and make you get a bigger entrance, because of the likely potential for simultaneous use - for example if the basement not only has a dryer plug, but also it's own full bath and a kitchenete area, and an exterior entrance. When in doubt, contact your local codes authority before you do anything expensive.

Table 310.15(B) Conductor Types and Sizes for
120/240-Volt, 3 wire, Single Phase Dwelling Services
and Feeders. Conductor Types RHH, RHW, RHW-2, THHN,
WHHW-2, SE, USE, USE-2

Copper	Copper or Copper clad Aluminum	Service or Feeder rating in Amperes
4	2	100
3	1	110
2	1/0	125
1	2/0	150

1/0	3/0	175
2/0	4/0	200
3/0	250	225
4/0	300	250

250	350	300
350	500	350
400	600	400

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Free NEC Electrical Load Calculation Software for Single Family Residential Homes

NEC Standard Method Single Family Residential - Electric Service Entrance Load Calculator