What Size Circuit Breaker Do I Need?

The Golden Rule: Size the Breaker to the Wire

The breaker protects the wire, not the appliance. The breaker size must match the ampacity of the wire gauge used:

14 AWG wire → 15-amp breaker maximum 12 AWG wire → 20-amp breaker maximum 10 AWG wire → 30-amp breaker maximum 8 AWG wire → 40-amp breaker maximum 6 AWG wire → 55-amp breaker maximum 4 AWG wire → 70-amp breaker maximum 2 AWG wire → 95-amp breaker maximum 1/0 AWG wire → 125-amp breaker maximum

Never install a breaker larger than the wire can handle.

The 80% Rule for Continuous Loads

For loads that run continuously for 3 hours or more (HVAC, water heaters, EV chargers), the NEC requires the breaker to be sized at 125% of the load — or equivalently, the load should not exceed 80% of the breaker rating.

Example: a 7,200-watt electric water heater at 240V draws 30 amps. 30 × 1.25 = 37.5 amps → use a 40-amp breaker.

Common Appliance Breaker Sizes

Standard residential applications:

General lighting/outlets (15A circuit): 15-amp, 1-pole Kitchen small appliances: 20-amp, 1-pole Refrigerator: 20-amp, 1-pole (dedicated) Dishwasher: 20-amp, 1-pole Microwave: 20-amp, 1-pole (dedicated) Electric dryer: 30-amp, 2-pole Electric range/oven: 50-amp, 2-pole Central AC (3-ton): 30–40-amp, 2-pole (check nameplate) Central AC (5-ton): 40–60-amp, 2-pole (check nameplate) Electric water heater: 30-amp, 2-pole Hot tub/spa: 50–60-amp, 2-pole EV charger (Level 2, 48A): 60-amp, 2-pole

How to Calculate Breaker Size for a Custom Load

1. Find the wattage of the load (from the nameplate or spec sheet) 2. Divide by the voltage: Amps = Watts ÷ Volts 3. For continuous loads, multiply by 1.25 4. Round up to the next standard breaker size (15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100) 5. Verify the wire gauge supports that amperage

Example: 4,800W electric baseboard heater at 240V → 4800 ÷ 240 = 20A → × 1.25 = 25A → use 30-amp breaker with 10 AWG wire.

Industrial and Commercial Sizing

For motors, the NEC requires breakers sized at 250% of the motor's full-load current for standard motors (for short-circuit and ground-fault protection), with separate overload protection. This is different from the residential approach and requires careful calculation per NEC Article 430.