Free Circuit Breaker Sizing Calculator
Determine the appropriate circuit breaker rating for a given load current with safety margin.
A
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Minimum Breaker Rating
50.0 A
Suggested Standard Size50 A
Minimum Breaker Rating vs Full Load Current
Circuit Breaker Sizing
The breaker must protect the cable while allowing normal load current to flow.
Sizing Rule
Minimum breaker rating = Load current x 1.25 (125% per NEC for continuous loads)
Then select the next standard breaker size at or above this value. The breaker rating must also be at or below the cable ampacity to ensure the cable is protected.
Example Calculation
A 40 A continuous load with 125% safety factor.
- 01Minimum rating = 40 x 1.25 = 50 A
- 02Standard size = 50 A breaker
- 03Verify that cable ampacity is at least 50 A.
Frequently Asked Questions
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