motor failure 2

[humbleuser]

I don't hang out in this forum anywhere near enough as I should. This is great technical site. However, I do have a question that I'm hoping some of the more experienced mebers can answer. Keep in mind that I'm not a trained electrician; I'm more of general maintenace type of guy

I have 25 HP G.E. motor (230/460 3-phase) attached to an injection molding machine. I saw this machine running and making parts prior to me buying it. The place where it came from had it wired for 460. I brought it and rewired it for 230. The motor ran for about 5 minutes, somewhat noisy, before it started smoking and tripped the breaker. The shop that is rewiring it told me that I had the proper wire connections to the motro. I asked him what caused it to burn out? He's not sure. He says the bearings aren't in bad shape. he thinks that some of the 'varnish coating' on the windings may have worn out. It's possible that some condensation on the worn area may have caused the motor to short out. Is this possible? Thanks in advance.

 

[stardelta]

I am pleased to hear you have finally sorted out the issue and the machine is now earning money!. I must add that I think this thread has been particularly informative and would be surprized if all the the contributors have not learned something from the comments of the others. I for one have (TQ Jraef)

 

[aolalde]

To me this problem was a classic mess created by the limited knoledge on electric motors of both, the user and repair shop. However that seems to be the normal way that lot of bussines run nowdays.

 

[humbleuser]

Hey, I'm a molder not a motor repair man

 

[aolalde]

I apologize for being sarcastic, but if a motor expert should be hired on time shouldn’t you avoid all problems and money expenses?

 

[l3city]

aolalde:

"humbleuser" is not an electrical expert (neither do us, we are humans) he said that in the begining, thanks for the apologize (2-tumbs up for you) We are here to try and answer/help for different situations, as in "humbleuser's" situation for example.
regards

 

[moira]

Hi, Humbleuser: I think, you are a credit to yourself and who ever you work for! You had your problems, but stuck it out and accomplished what you were intrusted to do! You did a GOOD JOB! Hopefully for all of us, our work can be one continuing educational process. Only a few years back, none of us would even had the pleasure our recent conversations. Keep up th good work! MOIRA

 

[humbleuser]

Thank you moira. I'm the owner of a modest injection molding company. So basically, I'm the maintenance man, purchasing agent, set up man, salesman, tooling engineer, expert troubleshooter...you get the picture. I do have a few people working for me such as operators and foreman. But the delicate stuff like changing motors, insert changes, quoting jobs, etc. I do myself for peace of mind. This forum has been extremely helpful.

 

[jraef]

Thanks humbleuser, glad we could help. Don't mind aolalde's grumpiness, he isn't usually like that and has been offering a wealth of knowledge here for quite a while. But we all get a little tired of people who attempt to use the Internet in lieu of hiring the right person, while some of us "right persons" are sitting idle or getting laid off. It's not your fault, it's just the way things are now. In actuality you did do this correctly for someone who had to do most of it themselves, you just got hooked up with a rewind shop that appears to be in want of some additional expertise.

Post their info so we can all send them an invoice (just kidding)!

http:/

http://www.jraef.com

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[stardelta]

I sympathise with Humbleuser, he has had an avoidable issue that has cost him money both in repair costs and in downtime. I do think it true to say if proffesional advice had been sought from the outset the bill would have been much lower. However if these situations never arise people like myself and the many others employed in the repair industry would be out of work.

 

[oftenlost]

GE motors seldom have thermisters. Most often, they utilize Klixons, which are sealed thermal switches manufactured by Texas instruments. I would be concerned with an internal thermal set for 165C unless the winding and leads were Class H

 

[Skogsgurra]

Humble,

Are you sure that the wires were marked "PC"? That does not make much sense - no one uses PC for a PLC. I think the marking was "PTC", which means Positive Temperature Coefficient and is used to distinguish PTC from NTC. PTC is the type used in motors because they have a well defined switching temperature. NTC is more of a measuring component with a smooth resistance curve.

Gunnar Englund

http://www.gke.org

 

[humbleuser]

The lead read "PC". The repair shop said that there was a thermistor installed but they had forgotten to install it initially. They sent a guy out he installed it here at my shop. The motor seems to be running just fine now.

 

[powerjunx]

humbleuser,
I also read such leads before as PC - a two lead wire temperature sensor. But i wonder why GE used this marking to specify its purpose.

Anyway, skogsgurra is on the right track. PC is somewhat used to be as PTC.