Thought I would put this up here and see if anyone has any guesses as to what is going on. Some back ground I work on a ship, the distribution systems is ungrounded delta. We had a steam heater blower that rotation was backwards on, it's been been installed for years and has always spun the right way, only work done on the circuit that I can remember is replacing the switch with a thermostat last October or so, rotation was correct after that. Thermostat controls two heaters other one didn't change rotation. Other engineer wanted to switch leads which shouldn't have any effect since this is a single phase 120 volt motor. Switched L1 and L2 at thermostat ( it's a double pole thermostat by the way). Test ran and blower now had correct rotation, other motor remained the same(correct rotation ).
I thought this was odd since changing legs should not change rotation on a single phase motor, now comes the really weird stuff. I replaced the thermostat cover and motor reversed rotation (wrong way), again other motor not effected. Removed thermostat cover and again correct rotation. Loosey reinstalled thermostat and have correct rotation. I don't believe that there is any grounds as or shorts as they don't show on our ground detection system and breaker is not tripping.
Has anyone seen anything like this? I don't do a lot with single phase motors so I'm no expert but this is mystery to me any thoughts on what is going on?
Thanks
JD

Coating worn off of the wires at the thermostat and making contact with each other when you push the cover on?

My thoughts are you're dealing with a Delta system, I worked as a lineman and the difference between Delta and Wye as to fuses opening is a delta can "see" a ground as "load" ,Wye system almost always opened.

Are you thinking "open delta"? I thought that the system was put to bed a long time ago. Lots of older cities and industry buildings were this. The main concern is the system results in un-balanced voltage between the legs. I would venture to think that the thermostat has a grounding issue when the cover is replaced.

Troubleshooting wise it sounds like you have narrowed it down to something locally at the thermostat. If you can turn the problem on and off from there I would stay there. Change the thermostat or remove it and hard wire it and see what you get.

We've still got some open delta services here. The (This word is unacceptable on Trapperman) leg is quite often unmetered too...lol. If a bug blows you just swap it out. The closed deltas need a dual bushing bug. We've converted it to open delta for a day or two while someone gets a dual bushing bug from central stores in the city.

The ships got a delta system so zero reference to ground. How many wires going to the motor? The current has to have a place to go or return to. Is the generator delta and the system introduces a ground at the main?
Ships are weird man!

Single phase motors have no starting torque. Once they start turning they will run that way. There are three electrical ways to make them turn in the direction you want. Split phase windings, capacitor-type windings, and shaded stator poles. You may have a problem with your starter circuits?

Thanks for the reply. I agree that the problem is in the thermostat box, or the cable going to the motor that changes rotation. It's working for now and we will be out of our heating season in couple of weeks, and I'll try to get it fixed and working right.
Jake it is a single phase motor so two conductors going to the motor, each leg has 60 volts to ground( the hull) for 120 between them,

It is an ungrounded delta? Something don't make sense here?

You sure there is not a delta/Y conversion somewhere?

I think maybe it is grounded in the middle of one leg of your delta. That would make 120V across line to line and 60V Line to ground.

I'm sure there's no Wye to Delta transformer. I don't think that the unground delta is used anywhere besides ships today and most people are kind of confused by it by I dod't think Ive worked on a ship that was not. I believe it is used because in theory it is safer, you can touch one phase and the hull and there is not a current path, of course that not really true There is always some leakage somewhere, but there is a ground detection system that lets us know if this gets high. I've really only work on ships so it seems normal to me, I get confused in houses and other shoreside systems.
60 volts on each leg is what is normal here.
JD

Does it use the 3 light system as ground detection?

I've heard of it being used in older facilities but I don't think I've ever worked on one. Seen my share of corner grounded systems though. Kinda weird to see when you open one of those panels.

Mike

Yep thee lights, one for each phase, dim, or out is grounded to the hull. As Shakeyjake said ships are wierd.

I would verify there isn't anything wonky with the thermostat... Then I would check the capacitor(s) at the motor in question. Supposedly a faulty cap can cause a single phase motor to rotate backwards... I've never seen it. But I rarely deal with them... Most of my work is industrial 3 phase motors.

It could be one thing or a combination of things. Just have to eliminate what it ain't to find out what it are.

Mike