The wire gauge for a 240-volt circuit is determined by the circuit breaker amperage, not by the appliance wattage alone. A 20-amp 240V circuit requires 12 AWG wire. A 30-amp 240V circuit requires 10 AWG wire. A 40-amp 240V circuit requires 8 AWG wire. A 50-amp 240V circuit requires 6 AWG wire. A 60-amp 240V circuit requires 4 AWG wire. This sizing comes from NEC Table 310.16 for copper conductors in a dry residential environment and applies to dryers, water heaters, AC units, EV chargers, ranges, and any other 240V appliance.
Why 240-Volt Circuits Need Heavier Wire
A 240-volt circuit delivers twice the power of a 120-volt circuit at the same current level. Combine that with the fact that 240-volt appliances typically draw higher amperage than 120-volt devices, and you get circuits that must be sized for real continuous high-current demand. A 30-amp 240V circuit can deliver 7,200 watts continuously. A 50-amp 240V circuit delivers 12,000 watts. These power levels require copper conductors large enough to carry the full current without overheating, which is why every 240-volt circuit in a home uses heavier wire than any standard 120-volt branch circuit.
Cable Type for Common 240-Volt Applications
Most residential 240-volt circuits inside walls use NM-B (Romex) cable in the appropriate gauge. A 30-amp 240V water heater or dryer sub-feed uses 10/2 NM-B. An electric dryer with a 4-wire NEMA 14-30 outlet uses 10/3 NM-B (three conductors plus ground, because dryers require both hots, a neutral, and a ground). A 50-amp electric range circuit uses 6/3 NM-B for the same reason. For exposed or outdoor 240-volt runs, use UF-B cable rated for direct burial or THHN individual conductors in PVC or EMT conduit. The required gauge does not change based on cable jacket type, only on breaker amperage.
240-Volt Wire Gauge Quick Reference Chart
20-amp 240V: 12 AWG, 12/2 NM-B. Uses: small window AC, 20-amp EV charger outlet, pool pump. 30-amp 240V: 10 AWG, 10/2 or 10/3 NM-B. Uses: dryer, water heater, 30-amp EV charger, AC disconnect. 40-amp 240V: 8 AWG, 8/2 NM-B or THHN in conduit. Uses: 40-amp EV charger, large HVAC disconnect. 50-amp 240V: 6 AWG, 6/3 NM-B for appliances needing neutral. Uses: electric range, large welding outlet. 60-amp 240V: 4 AWG, THHN in conduit or SER cable. Uses: hot tub, large subpanel feeder.
Voltage Drop on Long 240-Volt Runs
For 240-volt circuits longer than 75 feet, check voltage drop before finalizing your wire size. On a 30-amp 240-volt circuit running 100 feet in each direction (200 feet total conductor length), 10 AWG wire produces approximately 3.5 percent voltage drop at full load. Upsizing to 8 AWG for that run keeps voltage drop under 2 percent. The NEC recommends 3 percent or less on branch circuits. Excessive voltage drop causes motors to run hot, heating elements to produce less heat, and appliances to cycle longer.
IB Lighting stocks 10/2, 10/3, 8/2, 6/2, and 6/3 NM-B alongside THHN in all standard gauges. Browse our electrical wire and cable selection. Free Freight Insurance Included on every order. Call (800) 674-9019 for sizing help or contractor pricing.