AmpSizerAppliance and equipment circuits
Some equipment is not just a load. A charger is continuous, a motor has a table of its own, a hot tub needs a disconnect you can see, and a mini split states its own minimum circuit ampacity.
EV charger circuit calculator
Charging amps in. Breaker, conductor, ground and conduit out.
Generator size calculator
Running watts and the biggest motor's surge in. Generator size out.
Hot tub wire size calculator
Nameplate amps in. Conductor, GFCI breaker, ground and conduit out.
Mini split wire size calculator
MCA from the nameplate in. Conductor, breaker and disconnect out.
Motor amps calculator
Horsepower and voltage in. Table full-load amps, wire and breaker out.
Transformer sizing calculator
kVA and both voltages in. Primary amps, secondary amps and protection out.
The circuits that get sized wrong are almost never lighting and receptacles. They are the ones with a nameplate on them, because the nameplate speaks a different language depending on what the equipment is: running watts on a generator, full-load amps on a motor, minimum circuit ampacity on a heat pump, kilowatts on a charger.
Each of these six starts from the number the equipment actually gives you and ends at a conductor, a device and a ground. Where a piece of equipment has a rule of its own — the continuous multiplier, the motor tables, the disconnect within sight — the page names the article it comes from.
Frequently asked questions
Why does equipment get its own rules instead of just amps?
Because the code treats different loads differently for good reasons. A motor draws several times its running current for a second at startup, so its breaker is allowed to be much larger than its conductor. A charger runs for hours, so it is a continuous load at 125%. Air conditioning states a minimum circuit ampacity that already includes the multiplier. Treating all three as plain amps gets all three wrong.
Why does my mini split nameplate say MCA and not amps?
Minimum circuit ampacity is the number the manufacturer worked out for you: 125% of the largest motor plus the other loads, per 440.33. You size the conductor directly from MCA with no further multiplier. The nameplate also gives a maximum overcurrent protective device rating, and that one is a ceiling, not a target.
Do I use the nameplate current for a motor?
Not for sizing conductors and devices. 430.6(A)(1) sends you to Tables 430.248 and 430.250 instead, and those figures are often higher than the nameplate. The nameplate current is what you use for the overload relay, which is the one place the actual motor matters more than the table.
Does a 50 amp RV plug need a neutral?
Yes. A 50 A RV receptacle is a 14-50R: two hots, a neutral and a ground, four conductors, because the coach runs 120 V circuits off each leg. A range or a hot tub with no 120 V loads inside it may only need three. Getting this wrong is how people end up pulling a second cable.
How we calculate this
kVA × 1,000 ÷ (k × volts) with protection at 125% (450.3(B)). Conductors, devices, grounds and
raceways then come from the same tables as everywhere else on this site.Sources: