Compressor pressure switch

[FrkyMnky]

So I have burnt up two pressure switches and I'm not sure what it causing it. The only thing that has changed is me wiring up the shed for 220, so that leads me to think I did something wrong with the wiring. Everything works great until it reaches shutoff pressure and then I get a nice puff of smoke and a little fireball. If I plug the line power directly into the motor leads it works great, just I have to shut it off manually.

Right now it is wired up through a 2 fuse SQD safety switch. The fuses are rated at 30A each. I have each line going to a separate fuse and then the ground going to the ground bar. Im not sure what the wire is actually called, but I am running liquid tite conduit with stranded #10 copper from the safety switch to the pressure switch. Colors are red, black, and green. Its hooked up as red/white, black/black, and green/bare in the safety switch. Inside the pressure switch its hooked up the same with red/white, black/black, and green/green with the red/black being the line/motor leads. I thought maybe it wasn't getting enough voltage because of the distance of the run at 225', but I'm using #2 the whole way and the compressor is the only draw at the moment at ~15A, so I have a hard time believing that. Both lines are getting 123v while running, so I don't think that is the problem. I have another 220v receptacle that is wired but I am a little hesitant to try it and screw up my welder. Im not popping any breakers so I have got to think its a problem down stream of the panel.

The compressor is a 60gal Kobalt, pretty standard with a 3.75hp motor. It was working just fine before we moved and it was hooked up using a standard 3 prong plug so I could share the outlet with the welder.

 

[nehog]

Post pictures of everything (wiring) with enough clarity and resolution so we can see where wires go. Also post the model of the pressure switch.

 

[C96]

Would like to help, but:

 

[JoeFin]

does this look familiar

BTW: check the motor connections inside the motor with a multimeter just to make sure nothing shook lose during transport

 

[FrkyMnky]

Here are the pictures guys…

I didn't take a picture of the panel, but its white/black to each pole on the 30A breaker and bare to ground. I will check the motor tomorrow and I am going to hook up the line leads directly to the motor wires so I can get a amp reading. I can't think it would be the motor considering it is running fine, but I will still double check.

BTW, its hooked up with 10/2 the same as it was in our old house on the 30A breaker. Draw for the motor is 15A rated.

 

[FrkyMnky]

Forgot to add its a campbell hausfeld gr004500AJ switch. That was the second one I blew, the first one was basically the same switch except it was a 125-155 instead of 95-120. Both times, the contact on the black wire side was the one that burned up.

 

[nehog]

FWIW, the switch seems to be wired correctly. Double check to make sure the motor works correctly on 240 volts.

 

[FrkyMnky]

Yea I'm still not sure what could be causing this. Thats the part that *****, I have no idea why on shutdown I would burn up a contact. I would expect it to be on startup.

 

[Bmwsyc]

You are going to get some arcing when you open the contacts under load. Is there a label on the pressure switch with the current rating?

 

[6768rogues]

My compressor ate its pressure switch shortly after I bought it. I called the compressor manufacturer and they said they switched from Square D to another brand and had nothing but trouble, so they switched back to Square D. They sent me a Square D switch free of charge and it has been working reliably for almost 20 years. Not saying that is what happened to yours, but it is what happened to mine.

 

[FrkyMnky]

The pressure switch is a cheap Condor POS, but the contacts are rated for 26A. The only thing I can think of is that the motor is pulling too many amps and while the contact is working while its connected once it tries to disconnect; **** up in flames. Looks like it could be either the run capacitor or the motor windings. I was thinking of swapping out the 30a fuses for 20a as a poor mans amp meter so I can figure out if its drawing too much. Im hoping its just the pressure switch though as I don't think the motor would fully charge the tank to 160psi if it wasn't working correctly.

Oh, the thermal protection isn't popping on the motor either so I don't think its drawing too many amps.

 

[LS6 Tommy]

You might be on the right track with the capacitor thoughts. Do you know for sure if it's a start cap or a run cap? Many single phase compressors have both. It wouldn't want to start at all if the start cap was bad. It would be an odd situation, but if it has an unloader, it may start with a bad run cap, then as the pressure builds the load goes up on the motor until the switch opens, causing the big arc. IDK, maybe that's far fetched.

Tommy

 

[FrkyMnky]

So I checked the current on both lines while running and its pulling a steady 15a. I didn't see much of a jump during startup, but the meter I was using is pretty cheap so it might not be fast enough to catch the startup current. At this point now I am more confused than before when I thought it might be the capacitor. Im going to hook up the new pressure switch and take readings while its running and when it shuts off to see whats going on. Hopefully nothing happens and it was just a crappy switch, but if it does then maybe ill figure out what is going on when it happens.

 

[FrkyMnky]

Well for everyone that helped and everyone that was following this, it turned out to be the pressure switch. Im not sure how I ended up blowing 2, but third one was the charm. Im not 100% sure it wasn't drawing too many amps as I lowered the pressure from 155 to 120 with the new pressure switch. Hopefully everything is good and I don't have a capacitor die in a few months. Oh, forgot to add, startup current was 25a, running 0psi was 11a, and when it cut off at 125 it was pulling 15.3a. Its rated as a 15a 3.7hp compressor. I don't think it would pull more the 16a at the full 155psi, but I'm not trying it until TSC gets more switches in stock just in case.