humming transfer switch

Time to do transformer lamination temperature checking. Not for amateurs. If temp is normal, suspect switching contact point resistance degradation. Time for a pro I'm afraid...

Humming from a Transfer switch can be caused by AGE. It can be caused by the lack of 60 htz voltage frequency(not normal 120 volt supply). It can be caused by fluctuating 120 supply voltage---the CG voltage is low and fluctuates from the amount of RV'ers using the 120 service. They all will be quiet when new and the 120 voltage is within range. Doug

We noticed ours did this after a power out and power came back on, or running the generator and switching back to the electric service. Like maybe the transfer switch wasn't totally switching over, but everything worked fine. If we shut main circuit breaker off at he electric service box, waited a second or two and turned back on just like we would be doing when just plugging in, the humming of the transfer switch stopped. No loose connections.

All the time for what total length altogether? Transformers hum. Good mounting and isolation lessens the noise. Suddenly louder humming is an immediate attention point. So is abnormal heat. The nearest I can pinpoint my Sola transformer hums in D Major. That's why it is in the utilty room.

Moved from Forum Technical Support

Many transfer cases make noise. They should not!
It can be caused by loose connections inside and loose coils inside.
I would disconnect from power sources, remove lid from unit, and check for loose connections.