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Can you apply a standard rated breaker at 100% of its rating if it is set to less than 80% of its maximum rating or sensor size?

Published date: 18 May 2020

Issue:
Is it OK to use an 80% rated breaker at 100% if set to less than 80% of its max. rating?

Product Line:
Circuit Breakers

Environment:

Powerpact and other breakers with adjustable Overload settings

Resolution:
The circuit breaker rating is the LTPU (Long Time Pickup) setting whether it is at 100% of the sensor rating or a lower amperage.  The fact that it is adjustable has no bearing on the fact that this is the breaker rating and there is no language in UL 489 or the NEC to indicate otherwise.  One could make a case for allowing application at 100% if the breaker LTPU is less than 80% of the maximum setting, but this is not how the standards are written or how the breakers are marked.  Bear in mind also that 100% rating not only requires breaker certification but there are cabling requirements also that would not be controlled if standard rated breakers were given license for 100% application if set to 80% or less of their sensor size. 

This question is not addressed directly in the NEC or UL, but it is addressed by the application statements and guidelines for standard and 100% rated breakers which do not allow 100% application for any breakers but those so marked.  For reference, please see the attachment and NEC 210.20(A)  and NEC 215.3.

Note that 100% marking is required only for continuous application at over 80% of the breaker rating (3 hours or more).  Shorter periods of operation up to 100% of the breakers rating are allowed.
 

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