480 motor help please. - Page 2 - Electrician Talk - Professional Electrical Contractors Forum

nap · 05-15-2008, 03:49 PM

Quote:

Originally Posted by TheRick

As far as the pump interference issue, if it is a mechanical issue it should be tripping the motor overloads and not the circuit breaker.

!

depends on how much interference there is. If it is basically locked, it will trip the breaker before it trips the overloads. This thing trips instantly. I do not believe it is totally locked. OP siad he could turn it by hand. not sure if he meant while mounted or not though.

So, the motor will run with no load on it and the starter will operate with no motor attached.

So, that would seem to leave either the wires to the motor, the pump but it would need to be nearly locked to cause this or the breaker is too small, but if so, it shouldn't be by much.

Do you have a larger breaker available just to toss in for a test? Do you have a meter that will read inrush current?

TheRick · 05-16-2008, 06:42 AM

Quote:

Originally Posted by nap

Do you have a larger breaker available just to toss in for a test? Do you have a meter that will read inrush current?

Before trying the bigger breaker Megger the conductors from the starter to the motor!

If they are good then try the bigger breaker, while measuring the current.

gardner · 05-18-2008, 10:00 PM

cdnelectrican, You hit the nail on the head!
The problem was..... The origional c.b. did not have any trip settings. It was not a motor rated c.b.. Again, it was working fine for many years. I finally took the c.b. in to have it tested. They came back with the response with " this c.b. is bad, what is it running?" I told them a 50 to 75 h.p , 480 volt motor. He then smiled and gave me a 150 amp, adjustible trip c.b. Motor rated for in rush current.
This solved the problem. I had problems with in rush current tripping the c.b. for transformers, but never a motor.
Also, The amperage rating is now at f.l.a. arround 75 amps ? It used to be 62 amps from privious readings. This may not be the same motor.
The heaters were replaced.
Lesson learned.
Thanks everyone for your input.
Kris.

wwilson174 · 05-21-2008, 02:24 PM

All your test results are normal. Just make sure you are using an MCB with adjustable magnetic trips. Then dial the setting to the point where the problem disappears Good luck, BillW

Betobeto · 08-19-2009, 08:20 PM

I had the same problem on a 480v 150hp motor...Pitting on the out side of the starter contacts causing a reflective wave (high Voltage)to trip the magnetic breaker . the fix was easy i replace the contacts. the motors been in service for 2 years