I have a contactor that is powered by a 12V transformer inside of a distribution box.
When I get a brownout, the thing turns off (expected) but then it turns on and it starts humming, until I hit the switch manually to turn it off and then turn it back on.
Its literary a filter, transformer (12V) -> contactor.
Why does it buzz after it auto triggers but stops buzzing when I switch it on? It makes a thud and everything when it turns itself on after a sag. I can't imagine what is different between the two turn on modes, I even took it apart before and checked the springyness of it (well not with a relay/contactor tester but still it felt decent). How is it loading the transformer to buzz? It's actually REALLY obnoxious. It has that evil street electricity noise. Its not loaded by anything external (test equipment which is all turned off with mechanical switches).
its been very consistent so long I reset it manually, as annoying as it is.