Circuit Breaker Sizing Calculator
Calculate proper circuit breaker size based on load and safety factors
About this calculator
A Circuit Breaker Sizing Calculator helps determine the appropriate circuit breaker amperage rating for electrical circuits based on the connected load and required safety factors. This essential electrical tool ensures proper protection against overcurrent conditions while preventing nuisance tripping. By calculating the correct breaker size, electricians and engineers can maintain electrical safety, comply with NEC codes, and protect equipment from damage caused by electrical faults or overloads.
How to use
Enter the total load current in amperes that will be connected to the circuit. Input any applicable safety factors or derating requirements based on installation conditions. The calculator will determine the minimum required circuit breaker rating, typically 125% of continuous loads, ensuring code compliance and safe operation.
Frequently asked questions
What safety factor should I use for continuous loads?
Continuous loads require a 125% safety factor per NEC guidelines, meaning the breaker must be rated at least 25% higher than the actual load current.
Can I use a smaller breaker than calculated?
No, using a smaller breaker creates safety hazards and code violations. Always use the calculated size or the next standard size up.
How do I account for motor starting currents?
Motor circuits require special consideration for inrush current. Use motor full-load current ratings and apply appropriate NEC motor protection requirements.