ECN Forum Forums General Topics of the Trade General Discussion Area Emergency Generator Not Shutting Off

What is the most common cause of an emergency generator not shutting off after normal power is restored? Could it be something hanging up in the transfer switch?

...Is there a latching relay??

I'm not certain, please explain.

Some have a time delay so you have to have power restored for a pre-determined time. It could also not be recognizing the return of normal power. Who knows? It might not be an automatic.

I'm going back to it early tomorrow morning. I'm also going to check for stable utility power. I've just read if utility power is not stable it will not switch back.

You don't say if this is a service call or a new install. I would get the manual out and be sure the clock is programmed correctly and the dip switches are set right. Check the wiring diagrams too.

You may also want to check your return to normal delays (could be extended, I prefer 5 minutes minimum) and your cool down cycle, I prefer 15 minutes on larger units of over 100 kw. I have seen factory defaults of 1/2 hour each meaning an hour for retransfer and cool down, IOW it may be shutting down, just taking one heck of a long time to do it, some customers don't understand these things and panic.

We have had two very new (less than a year) Onan transfer switches cause generators to run when normal power was fin.

Both times a electronic board in the ATS went bad.

One Generator ran for 126 hours the other for TWO WEEKS! they where natural gas units so fuel was not an issue.

I also agree that it is probably a relay or control board.

Bob,
Were these nat. gas units life safety? Do they allow nat. gas units for life safety in your area?

...Well, we had a customer who put his in "test", and left it on all weekend, then couldn't figure out why it didn't turn off