# compressor problem



## erics37 (May 7, 2009)

What size motor is it? Like 50 horse or so? If that's the case, and it's on an inverse time breaker, the breaker is too small. Check NEC 430.52. Does it have separate overload protection?


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## greenman (Apr 20, 2012)

what size is the ol's,
and what is the L.R.C locked rotor current ?


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## zen (Jun 15, 2009)

erics37 said:


> What size motor is it? Like 50 horse or so? If that's the case, and it's on an inverse time breaker, the breaker is too small. Check NEC 430.52. Does it have separate overload protection?


i looked at the name plate but i couldnt make out the hp. it has a non fused disconnect at the equipment so no i didnt find any other overload protection..when i put an amp probe i got 74 amps on a phase and 61 on b and c phase..


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## zen (Jun 15, 2009)

greenman said:


> what size is the ol's,
> and what is the L.R.C locked rotor current ?


those are questions i have not learned about yet so the answer is i dont know, but having said that i will look them up and find out what they are and why i should know them


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## captkirk (Nov 21, 2007)

maybe the contacts on the starter are getting old and pitted...


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## greenman (Apr 20, 2012)

does it have a motor starter with over loads.
and it should have time delay fuses.


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## greenman (Apr 20, 2012)

Read this.
http://groverelectric.com/howto/20_How%20to%20Calculate%20Wire%20&%20Fuse%20Sizes%20for%20Electric%20Motors.pdf
http://www.littelfuse.com/data/en/Technical_Articles/nema_broch.pdf


zen said:


> those are questions i have not learned about yet so the answer is i dont know, but having said that i will look them up and find out what they are and why i should know them


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## Roger123 (Sep 23, 2007)

zen said:


> .when i put an amp probe i got 74 amps on a phase and 61 on b and c phase..


That seems to be the problem, since the name plate listed 57.6 RLA.


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## greenman (Apr 20, 2012)

Or the FLA
http://www.onlineconversion.com/motor_horsepower.htm


zen said:


> those are questions i have not learned about yet so the answer is i dont know, but having said that i will look them up and find out what they are and why i should know them


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## greenman (Apr 20, 2012)

I'm from canada so i do not know you codes but this looks good.
http://www.1on1tutoringlive.com/Motor_Calculations.htm
:thumbsup:


zen said:


> those are questions i have not learned about yet so the answer is i dont know, but having said that i will look them up and find out what they are and why i should know them


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## erics37 (May 7, 2009)

Sounds like it's time to meg the motor. If it's pulling more than the nameplate says it should be under full load, then it's either undersized or something's wrong with it. I lean toward the latter, especially given the discrepancy between A phase and B & C phases.

It also sounds like your motor circuit isn't protected up to snuff. Need to have overload protection of some sort, either an overload relay or a fuse block or something. Once that's in place then you can put in a proper size circuit breaker as well.


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## chicken steve (Mar 22, 2011)

Sounds like she's going to burn up soon.....~CS~


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## Wirenuting (Sep 12, 2010)

What brand is it?

If its a Quincy you can google the book online or give them a call. Then you can see how it should be set up. 
Like others have said, the motor is about toast and the breaker may be wrong. 

After you fix it, see if it has an unloading valve that's stuck closed. It should open after each cycle to relieve the head pressure. That's a sure way to kill a compressor motor.


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## hardworkingstiff (Jan 22, 2007)

I would caution against telling the customer that installing larger conductors to correct for voltage drop will cure the problem.

Like others have pointed out, it looks like there is something else wrong (although the small feed conductors may have contributed to this failure developing). 

Did you take voltage readings near the motor with the motor running?


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## Stickshaker (Jun 29, 2012)

Wirenuting said:


> After you fix it, see if it has an unloading valve that's stuck closed. It should open after each cycle to relieve the head pressure. That's a sure way to kill a compressor motor.


That's what I was thinking too.


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## Trigger_442A (Sep 15, 2012)

How do you know it's not a mechanical issue, if the compressor has run for years without problems don't instantly assume electrical, anyhow LRC is six time FLA so in your case it would be six times 58amps and then code gives you a percentage allowable for OC protection, I would do a load check while running to find out, load check on start up and while running should tell you something, maybe your breaker is getting old to?


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## swimmer (Mar 19, 2011)

I wrote the stuff below before reading previous posts. Looks like you are seeing too much current, there is no overload protection, and it is the breaker (not the overload) that is tripping.

Check contacts on disconnect. You may have arching and carbon build up on one phase causing an intermittent open. Motor then single phases and trips overload.


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