Circuit Breaker Sizing Calculator
Calculate appropriate circuit breaker size
About this calculator
The Circuit Breaker Sizing Calculator helps electricians, engineers, and homeowners determine the correct amperage rating for circuit breakers based on electrical load requirements. Proper breaker sizing is crucial for electrical safety, preventing fires and equipment damage while ensuring reliable power distribution. This tool eliminates guesswork by calculating appropriate breaker sizes according to electrical codes and safety standards, considering factors like continuous loads, motor starting currents, and safety margins required for different applications.
How to use
Enter your electrical load information including total amperage, load type (continuous or non-continuous), and any specific equipment requirements. The calculator will apply appropriate safety factors and derating requirements. Review the recommended circuit breaker size and verify it meets local electrical codes and manufacturer specifications for your installation.
Frequently asked questions
What's the 80% rule for circuit breakers?
The 80% rule requires that continuous loads (operating for 3+ hours) should not exceed 80% of the circuit breaker's rated capacity for safety and code compliance.
Can I use a larger breaker than calculated?
Generally no. Oversizing breakers can compromise safety by failing to protect wiring and equipment from overcurrent conditions that could cause fires or damage.
How do I size breakers for motor loads?
Motor breakers require special consideration for starting currents. Use motor full-load amperage from nameplate data and apply appropriate multipliers per electrical codes.