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John Walker
08-08-2011, 10:19 PM
How hot can contacts in contactors get before they weld? Taking running temp readings on each leg 3ph 460v average 100 deg to 130 deg multiple 50 ton systems. 60 amp contactor and 75 amp contactors.outside units amb temp 80deg...Thanks

Contactor
09-08-2011, 12:37 AM
Dt ambient? Inverse factor of load x thickness of copper conductor (mm) + specific density of terminal.

Please advise.

NB this will give + or - 5k at best

chilliwilly
14-08-2011, 11:37 PM
Its the arcing when they open and close that mainly causes them to weld, it doesn't matter if they are operating within specified design limits they will eventually splatter away or weld up due to wear and tear. If they have welded up whilst they are closed and are passing current, then they have to be overloaded at least twice their designed load.

The contacts of most switch gear aren't what they used to be, even if you double the AC3 rating of a contactor. The mechanical wear and tear will add to the premature electrical failure. Platinum contacts are the best choice, but they are very expensive. The arc baffles within the switch/contact assembly tends to be made from bakerlite which as we all know is no good for high temperature use, and they might as well not be in there for what good they are. The old abestos liners were the better choice, but the replacement is somewhat inferior.