×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

AC motor with grounding problem

AC motor with grounding problem

AC motor with grounding problem

(OP)
I have an A. O. Smith corp AC motor that has ground problem. It is on an air comp. and tank assy that was made in 1956. I was told when I bought it that I could not use a ground on it as it would pop the breaker and that they were meant to be wired with two wires for 115/230v without a ground. It is wired for 220v and I have used it for several years and it did in fact pop the breaker if you grounded it. I put a wire from the motor to a light base and wired the other side of the light to ground so I could see if it ever had a short causing high voltage to ground. The voltage to ground was about 30v. when I moved to a new location I had to reverse the motor wiring to get it running in the right direction. Now there is no voltage to ground and I am able to ground it without poping the breaker. Could it be that there is a winding that is shorted to ground or is this motor really made to work without a ground?

RE: AC motor with grounding problem

It doesn't matter much... That is a very dangerous situation... You should further your investigation.  It does indeed appear that you have a winding shorted to case.

Do indeed FIX THIS!!

I cannot imagine a motor as new as "56" being deliberately wired some how to ground.

Make sure that some flying wire whisker on some connector isn't touching the case.  If none are found JUNK THAT MOTOR.

RE: AC motor with grounding problem

(OP)
The real puzzle is that if I wire it for rotation in one direction the frame is hot. If I wire it for rotation in the oposite direction the frame is NOT hot. If there is a shorted winding it is shorted no matter how you wire it. This is not the case here. This motor is not acting like it has a shorted winding to me. Any ideas?

RE: AC motor with grounding problem

Start winding is shorted on one end. So the case gets hot based on which side is hooked to the hot verse neut.

Why on earth did you post this in the solidstate relay forum there are a bunch of motor specialists in the MOTORS forum..

RE: AC motor with grounding problem

(OP)
itsmoked, what is the web address for the motors forum? I googled for a motor site and this is all that looked good.
It does have a start relay built in to it. Is this repairable or will it have to be rewound?

RE: AC motor with grounding problem

Before you go to the motors forum go to the top of this thread you've started.  Highlight the "thread956-142808"
and copy it.

Click the "Browse Forums" at your upper left panel under your log in name.

Scroll down the list of furoms to the Electrical Engineering section.

Pick the Motors forum.

Start a new thread in that forum.
Mentiion you mis posted a motor question in the relay section but you would still like comment on it.
Then past the previously copied thread number "thread956-142808".

They can just click on it an read it.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources