Technical FAQs

Ask a Question

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

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

Product Line:
UL489 listed molded case circuit breakers

Environment:
Field Testing and Maintenance Guide 0600IB1201  08/2013
Pages 17, 24 and 34

Cause:
Design criteria

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 micro Ohms)  for most circuit breakers can be found in the Field Testing and Maintenance Guide 0600IB1201, pages 17, 24 and 34.

Example:  From page 17, the pole resistance for a Powerpact H frame 15 amp breaker is 35,000 micro Ohms.  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

This breaker generates or loses  7.9 Watts per pole.  For a 3 pole breaker 7.9 Watt x 3 poles = 23.6 Watts
Was this helpful?
What can we do to improve the information ?