Loud hum from ESCO transfer switch

[Johnontheroad]

As per a previous thread, I replaced my IOTA transfer switch with an ESCO. Everything worked OK, no problems but I find that the ESCO transfer switch makes a loud hum that I find objectionable. I called ESCO, talked to an engineer who said not to worry, it is just 60Hz harmonics across the breaker contacts.

Still, it bothers me, mainly because I don't really know why it would hum and the IOTA didn't. And I am perfectly sure that it is wired correctly and all the contacts properly torqued down. So I'm just curious, anyone else have any experience with this type of issue?

[bgbranch]

John,
The esco has the relay energized when on shore power and the other relay energized on generator power resulting in your hum on shore or generator. I too am changing out my transfer switch but I'm using the Intellitec Switch. When on shore power, power travels thru a normally closed relay resulting in no hum while on shore. When the generator fires up it senses the power and energizes the relay to switch to generator. With this you only get the hum on generator power.

[Johnontheroad]

Figured it out. I thought if the hum comes from contact harmonics, maybe if I exercised the contacts? So I turned off AC, started the genny, and it worked fine. After the genny was warm I turned it off and went back to AC. Presto, no more hum.

Ron, the contacts on the ESCO main transfer switch are normally closed and the generator normally open. This means that while on shore power the relays are not energized, and when on genny then both relays are energized.

== John