motor contactor terminals fused together

[QGeek]

I have a report of two of the three motor phase terminals in a motor contactor being fused (shorted by melting) together. Twice in a row, same machine, same motor, same phases.
This is on a machine in the field. I was thinking it could be a short in the motor windings. We are operating 460VAC, 3phase.
What do you think?
Also, as far as testing, I guess we could compare resistances across the phases?
Any suggestions?

 

[Parchie]

Too little information for anybody to say. Is this a wye-delta starter? What's the contactor rating? What's the motor FLC? What's the available fault?

 

[jraef]

The TERMINALS of a contactor should not be so close to each other so as to have even the remotest chance of touching, but if they do, melting would then only be a possibility if there is such a bad protection scheme that it failed to clear the obvious bolted fault.

So either the report you received was completely wrong (likely) or your entire system is completely hosed and you need an Engineer to investigate it and redesign EVERYTHING about it.

I think it's more likely that your CONTACTS of one phase are welded, not the terminals. Contact welding can result from numerous causes, so still, more information would be needed, but check it out yourself and get the correct story.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[electricpete]

I’m guessing he means two of three contacts were fused closed (yes that might be incorrect use of the term "terminal" which leads to your valid question). Maybe op can clarify. Along with more details what specifically was observed when. What was done between these events.

=====================================
(2B)+(2B)' ?

 

[flexoprinting]

Hi Pete

Dunno Pete, how likely would that be? I have experienced the terminal connectors at motor fusing together on the older German machines, one would come loose and the two phases would arc but never seen two contacts fuse. I think Jeff's right on the money here.

Chuck

 

[QGeek]

Gents,
I appreciate your time and input more than I can say. Have reached out to my customer/contact for more info.
Will have a conversation and continue post with more details.
Thank-you.

 

[waross]

I've seen contacts burnt off, I've seen contacts welded closed and I've seen contacts welded open.
One cause is a short circuit. This tends to produce welding, but not always.
Another cause is a heavy load or short drawing the voltage down until the contactor drops out. The voltage recovers and the contactor pulls in. Often seen with standby generators with too much A/C load. The cycle repeats until either the protection clears the circuit or there is not enough contact left to complete the circuit. But again, not always.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

Dunno Pete, how likely would that be?

Since op appears unable to provide clarification, I’m not going to engage in any more speculation. My apologies for starting down that route.

=====================================
(2B)+(2B)' ?

 

[electricpete]

I guess you are suggesting two terminals shorted phase to phase or only one contact shorted closed. My interpretation of op is different, but I agree not as likely. I should have quite while I was behind.

=====================================
(2B)+(2B)' ?

 

[jraef]

Or, quit while you were ahead on that post...


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington