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What is meant by the ambient operating temperature of a circuit breaker?

Published date: 02 June 2020

Product Line:
Circuit Breakers

According to UL489, "ambient temperature" is defined as the temperature of the surrounding medium that comes in contact with the breaker or switch. For an enclosed device, it is the medium outside the enclosure.
Circuit breakers are calibrated for use at 40°C. If they are used at an ambient temperature below 25°C, or above 40°C, they should be re-rated. See the attached bulletin for further information on re-rating.

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