Residential power for appliance work: 120 V, 240 V, receptacles and protection

A US home is fed with two hot legs (L1, L2) and a neutral. Each leg to neutral is about 120 V; leg to leg is about 240 V. Most appliances use 120 V; electric dryers and ranges use 120/240 V, with heaters on 240 V and motors, timers, lights and controls on 120 V.

Dryer and range circuits come in two styles. A 4-wire circuit has L1, L2, neutral and a separate equipment ground; the appliance's neutral-to-frame bonding strap must be removed. A 3-wire circuit (L1, L2, neutral) is allowed only for existing installations under the code's exception, and uses the bonding strap. The 1996 NEC limited the 3-wire method to existing circuits; new circuits are 4-wire.

GFCI protection trips when current leaving on the hot does not return on the neutral (leakage to ground). Recent NEC editions extend GFCI to dwelling kitchen and laundry receptacles and to 125-250 V receptacles; the 2023 edition added specific appliances, but local adoption and amendments vary, so check the edition your jurisdiction uses.

AFCI protection trips on arcing signatures. Some motor-driven appliances can cause nuisance trips on older AFCI/GFCI devices; diagnose the appliance for leakage before blaming the breaker.

Dedicated circuits are commonly required by installation instructions for refrigerators, washers, dishwashers, disposers, microwaves and dryers. A shared or overloaded circuit causes nuisance trips and low voltage under load.