Ok..... First, you're dealing with a now antiquated contactor design for this application. (Although they still make them) If this were a newer design unit it would have self cleaning /wiping contacts, and for that matter it would be switching loads individualy with a number of smaller relays. Thats a lot of amperage to switch this way. If you're not going to go all the way and just suggest a full upgrade of the contactor, which may require a different panel or enclosure to the side, those contacts are garbage at this point. mxslick's suggestion is a good one, but but unless they make good
FAST and SOLID contact in the future this problem will only repeat....
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As a temporary fix to further troubleshoot, take some 400 grit, and then some 600 grit sandpaper to them and polish them up. Then some contact cleaner to get rid of the residue. Put the contactor together and test it with no load outside the panel. And check to see if this thing is operating properly with a smooth solid connction, and that it has good tension on the contacts when closed. It may be that the mechanism is binding....
Now.... It also may be that the 120 you see when it not loaded by the contactor is much less under the load of the contactor. And this might not be enough usable power to actuate the contactor fully. And may be the cause of those arching contacts.... (Also how are the secondary contacts, are they OK?) One cause of this might be what appears to be a loose nuetral by the discoloration of the conductor below. As this seems to be the panel nuetral, you might have some other problems all around soon...
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Although I think the smoke you saw was from the coils, was really just drifting from the contacts, the fact that you got voltage at them while it was diconnected sounds odd. Is it at all possible that there is not a fault in the coils to ground? What where you measuring this 120 to? Ground of the can, or the nuetral? Do you have excessive voltage ground to nuetral? (While the loads are on.)
Either way it sounds as though you have a brain teaser - let us know what it eventually gets found out to be.
[This message has been edited by e57 (edited 10-05-2006).]
