3phase motor question

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Before everyone chimes in I already know. I did the math, and know the code so I realize they should have pulled #8 they should have installed a motor starter not a lighting contractor and they should have installed a fusable service disconnect with dual element fuses I know. First question I will get will be so why did it work fine for 12yrs ??? Million dollar question who has answers ??
 
Smash said:
Before everyone chimes in I already know. I did the math, and know the code so I realize they should have pulled #8 they should have installed a motor starter not a lighting contractor . First question I will get will be so why did it work fine for 12yrs ??? Million dollar question who has answers ??
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Something has changed since the time when the motor was operating. Loose connection (anywhere all the way back to the transformer), bad breaker or connection to the buss, contacts in the lighting contactor may be bad.

That's why you have to troubleshoot to get information. Are there other three phase loads form this panel and if so are there problems and is there low voltage at the other loads?

About 20 years ago I go to a big paint store and they are haveing trouble with the AC units and it turned out to be a loose connection at a lug feeding the sub panel where the AC was getting power.
 
Smash said:
Before everyone chimes in I already know. I did the math, and know the code so I realize they should have pulled #8 they should have installed a motor starter not a lighting contractor and they should have installed a fusable service disconnect with dual element fuses I know. First question I will get will be so why did it work fine for 12yrs ??? Million dollar question who has answers ??
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I gave you mine....you fixed the first problem and now the next weakest link is causing another problem. Sure it ran fine for 12 years, right into the ground.
 
ActionDave said:
I gave you mine....you fixed the first problem and now the next weakest link is causing another problem. Sure it ran fine for 12 years, right into the ground.
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That next weak link may have been what caused the first motor to go bad. The motor going bad may have been a symptom and not the cause.
 
ActionDave said:
May well be. About three quarters of the calls I go that have to do with motors the problem is not the motor.
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Just the fact they are useing a lighting contactor as a motor starter would cause me to question it. Those things go bad after a few years even used as just contactors. If it's big enough to start this motor you can take it apart and look at the contacts. They may be burned and pitted all to heck. Then I would invest in a real motor starter with overload or heaters.
 
Smash said:
First picture was taken after I pulled the new motor. Also was told by Baldo rep that this motor will work fine at 208V even though nameplate does not list 208V. In hindsight I should have gotten a motor which are wound slightly different with a nameplate listing my 208v Also another reason I thought I fried the motor. But they tell me it's ok and the old motor lasted 12 yrs. Baldor does not know of summer brownouts in this area that could lower voltage even more during summer months
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That sounds kinda fishy to me. Nameplate 230/460V? Baldor E code motors are rated for 208V, the E1 are "usable at 208V" and F series are 230/460. "Usable" means to me "assuming everything else is designed perfectly".

http://www.baldor.com/mvc/DownloadCenter/Files/BR457
 
Might try shooting terminal connection s with an infrared camera to check for bad termination under load. Loose connections are one of our most frequent preventive maintenance finds.


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ptonsparky said:
As you do this note which combination has the best results as far as current imbalance on the individual leads. Use that connection. I've used that method on Open Delta with a Hi leg. Not sure if it does you any good on a Wye.
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My purpose wasn't suggesting to use this to correct imbalance. It's for testing. My last post wasn't really clear so I should append it.

Clamp meter wrapped around all three wires at once but without wrapping around the conduit: should read zero amp. Any reading here indicates winding faulting to ground.

The next step involves taking amps of each leg separately and writing down. The voltage imbalance could be caused by the motor in question. Visualize it as a triangular knob. You rotate the knobs as if you're turning a three pointed knob forward one corner. If the imbalance is essentially the same, it is the source. If you have a massive imbalance that follows the "knob turn", it's likely the motor with a partially shorted turn. The first test would only tell you a fault to ground. This test would hint you about shorting from layer to layer.

Mechanical overload is possible if a wrong pulley was used. Fan hp draw increase to the 3rd power of RPM increase.
 
The "just a loud hum" with no rotation at all strongly suggests something much worse than voltage imbalance, like single phasing. If the motor itself is in fact good, that is.

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jtinge said:
Might try shooting terminal connection s with an infrared camera to check for bad termination under load. Loose connections are one of our most frequent preventive maintenance finds.
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Good idea. We use the cheap under $20 harbor freight IR gun - not as snazzy but works too!
 
iwire said:
I agree and that is why to me current readings are as important as voltage readings for this troubleshooting.
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Anyone doing trouble shooting needs more than a Just a volt meter, or Just an Amp Clamp, or Just a Wiggy. We don't all need PQ meters but if I was starting over I would certainly think about something that could handle 3 Phase. Hindsight is a good teacher.
 
ptonsparky said:
Anyone doing trouble shooting needs more than a Just a volt meter, or Just an Amp Clamp, or Just a Wiggy. We don't all need PQ meters but if I was starting over I would certainly think about something that could handle 3 Phase. Hindsight is a good teacher.
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And I would pick a multimeter with inductance on it; I have easily found a partially shorted winding in 3ph motors more than once that way.
 
Smash said:
Before everyone chimes in I already know. I did the math, and know the code so I realize they should have pulled #8 they should have installed a motor starter not a lighting contractor and they should have installed a fusable service disconnect with dual element fuses I know. First question I will get will be so why did it work fine for 12yrs ??? Million dollar question who has answers ??
Click to expand...
Even if motor isn't designed to run on 208 volts - it will run for a long time on 208 before it has a catastrophic failure, if it is running below rated output that will buy some more time as well.

Why did it work for 12 years - you have not found the item that is failing that appears to be causing single phasing at times, it is a more recent problem.

Under voltage, overloading - those will take some life off the motor, but how much depends on other conditions. What matters the most before you have total failure is what temp does the winding insulation reach.
 
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