Determine the correct circuit breaker size based on load current and the 125% rule for continuous loads.
Input Parameters
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Calculation Results
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About this calculator
Quick Reference
125% RuleNEC requirement for continuous loads
Standard Ratings15, 20, 30, 40, 50, 60...
ContinuousRuns for 3+ hours
SafetyAlways consult a local electrician
Overview
In electrical engineering, circuit breakers must be sized to protect the circuit conductors. The National Electrical Code (NEC) generally requires that overcurrent protection devices for continuous loads (running 3+ hours) be sized at 125% of the load.
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Pro Tips
A continuous load is something intended to run for 3 hours or longer (e.g., lighting, HVAC).
The formula is: (Continuous Load * 1.25) + Non-Continuous Load.
The calculated value is usually rounded up to the nearest standard breaker size.
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Fun Facts
"Residential breakers are commonly 15A (lighting) and 20A (receptacles/kitchen)."
"Specialty appliances like electric dryers often require 30A breakers."
"Oversizing a breaker is dangerous because it may not trip before the wire melts or catches fire."
