contactors

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Mike Hamner

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When I parallel contactors do they have to be the same in size or just have the ampacity of my conductor?

I have a 350 AMP contactor and need 400 Amp the contactor I have is rated
at 2,200 amps lock rotor curent.

I think I'm going to have a big contactor on my shelf.

Please help and thank's for the info.

Mike
 
I don't know offhand if there is a code complaint about that or not, but if done, the units will not likely switch at precisely the same time, which means the one that lags will share a larger potion of the burden of breaking current.

If this were installed, I would want to cite 310.4(B)(5), and like to claim that they would need to be connected to identical devices to meet the letter of being "terminated in the same manner".

Otherwise, for fractions of seconds, repeatedly, we may be violating 310.10.
 
Yes I have the 350 amp contactor in service and two sets of 4/0 train cables coming off
of it and would like to just add one size four contactor to my control cabinet and increase my feeders from a 250 amp to a 400 amp service.

Thank you!
 
Mike, I suggest keeping the exsiting load on the existing contactor, and feeding the new load through the new contactor, if at all possible.

Otherwise, I wouldn't try paralleling dissimilar contactors. You can't control the division of current, and will likely overload the smaller one.

Added: Unless it's going to open under full load, I think the 350a unit will survive. What realistic loading do you think it will be subjected to?
 
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