Of recent times I have only worked on hydro's with a motion contactor before the star/delta changeover so it would have to weld both sides before it would stay running. Then there is a oil temp and motor temp thermistors to also monitor potential over running problems. Plus there is a run timer as well. So three to four redundancies to protect against this type problem.

I have had this a couple of times on Otis hydros with wye delta contactors . If the contact or welds up only killing the power will save your motor from eventually burning out. Best solution is the soft start , where customers wont go for that I change the fingers inside the contactors ( front and back ) annually .correct me I wrong but if you have good connections on all 3 contacts they shouldn't weld up. I know these days none of us get the time for proper maintenance like back in the day but its a ten minute job that saves hours of headache if you have to replace a motor.

I just had this happen on a 1230 with a Siemens softstart. Apparently security silenced the fire alarm at like 1 am and it wasn't til 6 am when they changed shift that they noticed the smoke filling the rest of th building.

I could not recreate it after we replaced the valve and the oil. MLT works correctly every time I test it. Has anyone ever heard of a softstart doing this? I have to think that the controller was providing the run signal somehow.

Did you replace the Siemans starter too? I ask because yes we have had that happen on a Thyssen hydro. It boiled the oil, ruined the valve, and if I remember right it had to do with the run input in the starter being shorted...unless there's more to the story that will go to someone's grave.

That is interesting. I could see something failing on in the starter run circuit but then work fine? It's certainly possible. I think I'm going to put an Artisan interval timer on the run input set to like 10 minutes. Maybe we'll replace the logic board too to cover our bases. Thanks for the input.

IDWT do you remember when the Siemens soft starts first starting dropping the resistor inside the starter? I thought one of the quick fixes was a jumper across the normally closed portion (7-8) maybe? Curious because that sounds like a sure fire way to have these problems with the soft start. I remember a few service guys telling me about it years ago...

I just finished changing out all the contactors with soft starts (4 cars). I spoke to our Siemens rep about possible solutions when the initial problem occurred and he told me that, though the soft starts prevent most of the problems with start / run contactors, it is still possible for a soft start to fuse internally. And even if you were to install a timed relay to dump the line, you are still relaying on a mechanical contact, which can fail. It all boils down to the old adage "Crap happens" though I feel much better having the soft starts installed.

Merry Christmas and Happy New Year to all!