What is an "HM" breaker?

posted in: Constant Current Products

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"HM" is short for "High Magnetic Load," which typically means the internal trip delay is designed for use with transformers or other devices that have a higher than normal inrush current. Standard circuit breakers can suffer from nuisance tripping because their internal delay will occasionally see in-rush current as a fault whereas an "HM" breaker sees it as normal operation.


In-rush current occurs when power is first energized and only lasts a fraction of a second, and is most severe when components are "cold," therefore in-rush current will not trip a standard breaker every time.