Electrical help. Load calculations

To determine the amperage service required by a residence that is supplied by a 240v single phase, three wire system, an electrician uses what formular?

Assuming you are determining your loads in volt-amps (VA), you would need to use one of the many forms of Ohm's Law to ultimately determine the current capacity (in amps...commonly called "ampacity") by this formula:

P = I x V, where
P = Power (in VA)
I = Current (in A)
V = Voltage (in V)

If you determine that your overall load is 31,200 VA, for example, you would apply this formula to determine the ampacity required:

P = I x V, where
P = 31,200 VA
V = 240 V
Solve for I

I = P / V = 31,200 VA / 240 V = 130 A

Tada!

The Electrician will take the connected wattage of all the devices attached to the electrical system, add them together and apply the allowed diversification factor from the NEC, then divide the wattage by 240 volts to get the minimum service amperage required.

Hope this helps,

Newton1Law

Current = Total wattage / 240V