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Topic: contactors and controlling single110 and 220v 3 phase power... (Read 2 times) previous topic - next topic


I was given the advice from two separate knowledgable sources to either run a 4 pole contactor and switch the 3 phases of the 220 and the hot leg of the AC,

I like this first option better, mostly because fewer parts = better reliability and there would less likely be a failure mode where you have one contactor power on and one power off due to mechanical or electrical failure.

If you must use two separate contactors, wire the output 120vac from the 120v contactor to control the 220 volt contactor. This would result in a 'interlock' feature where the 220v contactor could not activate unless the 120v contactor was also activated.



Hey guys thanks for the replies again, these are great comments and I've now decided that these safety circuits and power considerations are best left to an outside consultant or engineer.


I wanted to know any thoughts on the ramifications of using one circuit or two? i.e.

separate 3 phase 220 and single phase 110, OR pulling the 110 off of the 220 line. 
Is one a best practice concerning safety?
Are there noise/interference ramifications?


OR pulling the 110 off of the 220 line.

Where would the 110 neutral wire come from on the 3 phase 220 feed, a seperate wire from the service box? If you have to run an additional wire I would just have a complete 120vac circuit run from the service box and leave the 220 in it's own circuit.

Again best to let a local experianced expert (in both NEC and local building codes) help you design the installation.


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