Frequently asked questions

FA173884

20 April 2022

Issue:
How to calculate the heat generated by a molded case circuit breaker.  Watt loss per pole.

Product Line:
Circuit Breakers

Resolution:
The amount of heat a circuit breaker generates per pole (watts loss) can be calculated with the following formula: P=I^2 x R

• P = Watts loss per pole, in watts
• I = current in amperes
• R = pole resistance in ohms

The pole resistance (in microohms) for most circuit breakers can be found in the Field Testing and Maintenance Guide 0600IB1201.

Example: The pole resistance for a Powerpact H frame 15 amp breaker is 35,000 microohms.  Convert that to .035 ohms.
Now using P=I^2 x R, P = (15 amps) x (15 amps) x (.035 ohms) = 7.9 watts per pole