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Can 90 degree Celsius wire be used on a circuit breaker?

Issue:
Is it acceptable to use wire with 90 deg. C insulation on a molded case circuit breaker?

Product Line:
All MCCB's; legacy and Powerpact

Environment:
Electrical Distribution Systems

Cause:
Common requests to use 90 deg. C wire sized at the 90 deg. C ampacity because it is smaller and cheaper than the larger 75 deg. C wire.

Resolution
It is acceptable to use conductors with a higher insulation rating than what is marked on the breaker, but the ampacity must be based on the conductor temperature rating marked on the breaker.  So, circuit breakers marked for use with 75 deg. C rated conductors may be used with conductors rated for 90 deg. C if the conductors are sized per their 75 deg. C ampacity.

Also note:
  • Circuit breakers with a current rating of 125 A or less may be marked as being suitable for 60°C, 75°C only or 60/75° C rated conductors.  
  • Circuit breakers with a current rating of more than 125 A are considered to be 75 deg. C terminated devices, regardless of the temperature rating of the lugs.
  • Circuit breakers intended for continuous operation at 100% of rated current may be marked to be connected with 90°C rated wire with the size based on 75°C ampacity.
 
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