NEC-compliant breaker sizing
The NEC requires breakers to protect both the circuit and the wire from overload. Breaker size depends on load type and wire ampacity.
NEC Rules:
• Continuous loads: Breaker ≥ 125% of load current
• Non-continuous: Breaker ≥ 100% of load
• Motors: Breaker ≥ 250% of FLA (inverse time breaker)
Continuous loads: Run for 3+ hours (HVAC, lighting, pumps). These generate more heat and require oversized breakers.
Wire protection: Breaker must not exceed wire ampacity. 14 AWG = 15A max, 12 AWG = 20A max, etc.
Standard breaker sizes: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200 amps.
How to use: Select load type, enter current draw, choose wire size. Calculator recommends the next standard breaker size that meets NEC requirements.