A circuit breaker, panel, or switchboard is making a buzzing or humming noise

Issue:
Is it common for a breaker to make a buzzing noise? It is buzzing under certain loads.

Product Line:
Circuit breakers

Resolution:
Operational noise has been a question for a long time and it is generally a stacking up of factors which by themselves go unnoticed, but which together are noticed.

The attached product data bulletin contains the following information:

If excessive noise is detected, inspect the equipment for the following:
• Loose bolts, current transformer mounting, doors, covers and similar parts can resonate with the normal 60-cycle hum and cause excessive noise/humming.
• Extra hardware laying in equipment channels and similar type areas can cause excessive noise/humming.
• Open current transformers or improper wiring can cause excessive noise/humming.

If the equipment inspection does not identify the cause, there are internal components inside the circuit breaker that can affect the noise generated
while the circuit breaker is carrying current. Buzzing can be caused by micro-movements of ferrous materials inside the breaker due to the alternating magnetic field.

Square D has investigated several instances of reported excessive noise/humming. In most of these instances, loose hardware, wiring, and current transformers have been found to be the cause. In the few instances that this was not the case, the circuit breakers were evaluated and found to have acceptable performance and service life.

CONCLUSION No evidence has been found to indicate that operational noise/humming is detrimental to the performance or service life of the circuit breaker.

Released for: Schneider Electric Canada