Breaker Size Calculator | PES Supply
Breaker Size Calculator
Calculate the correct circuit breaker size for any load. Enter watts and voltage to get the proper breaker rating per NEC standards.
Standard Breaker Sizes Chart
| Breaker Size | Max Load (240V) | Max Load (120V) | Wire Size | Common Uses |
|---|---|---|---|---|
| 15A | 2,880W | 1,440W | 14 AWG | Lighting, outlets |
| 20A | 3,840W | 1,920W | 12 AWG | Kitchen, bathroom, garage |
| 30A | 5,760W | 2,880W | 10 AWG | Water heater, AC condenser |
| 40A | 7,680W | 3,840W | 8 AWG | Range, EV charger (Level 2) |
| 50A | 9,600W | 4,800W | 6 AWG | Large range, spa |
| 60A | 11,520W | 5,760W | 6 AWG | EV charger, sub-panel |
| 100A | 19,200W | 9,600W | 2 AWG | Main panel, large sub-panel |
NEC Breaker Sizing Rules
- Continuous loads (3+ hours): Size breaker at 125% of load current
- Non-continuous loads: Size breaker at 100% of load current
- Motor loads: Size breaker at 175-250% of full-load amps (starting current)
- Next size up rule: If calculated size isn't standard, go to next standard size
- Wire must be sized to match the breaker, not the load
- Solar DC breakers: Size at 125% of short-circuit current (Isc)
What size breaker do I need for a 2400W water heater?
2400W / 240V = 10A. With 125% safety factor: 12.5A → use a 15A breaker with 14 AWG wire. Most water heaters use a 30A breaker (allowing for larger units).
How do I size a breaker for solar panels?
For solar DC breakers: Take the panel short-circuit current (Isc) × number of parallel strings × 1.25 (NEC continuous) × 1.25 (irradiance safety). For example, 2 strings of panels with 10A Isc each: 10 × 2 × 1.25 × 1.25 = 31.25A → use a 30A DC breaker.
What size breaker for a Level 2 EV charger?
Most Level 2 EV chargers draw 32-40A continuously. With 125% safety factor: 40-50A → use a 50A breaker with 6 AWG wire. Check your charger's specs for exact requirements.