3 Phase Contactor with 120V coil.

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WNMG442

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I have have a 3 phase compressor with a Square D magnetic contactor. The contactor is wired 4 wire, with 3 phases and ground to the enclosure. The coil in the contactor is 120v. How do I wire that? I can tap off one of the phases for 120v, but there is no neutral. Do I use ground? Do I run another wire from the panel? I don't like the idea of potentially energizing something that shouldn't be energized.
 
WNMG442 said:
I have have a 3 phase compressor with a Square D magnetic contactor. The contactor is wired 4 wire, with 3 phases and ground to the enclosure. The coil in the contactor is 120v. How do I wire that? I can tap off one of the phases for 120v, but there is no neutral. Do I use ground? Do I run another wire from the panel? I don't like the idea of potentially energizing something that shouldn't be energized.
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I don't know if it will work in your application but a year or two ago I was asking the same question.
Everyone said Do Not Use the ground as your neutral.
They suggested a machine tool transformer.
It is a small transformer that you connect to two legs of your 220V 3 phase to get 110v.
I used one to power a small 110v coolant pump on my band saw. It turns the pump on/off with the saw's main start/stop switch.
 
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Those transformers are surprisingly expensive.
If you can run a neutral for less money, do that.
 
The three phase in my shop is generated and fed through a seperate sub panel. I can run a neutral from the main panel, but I don't know if that's kosher.
 
Running a neutral is perfectly kosher- it should be a white wire for code
 
If you're going to run a neutral from your main panel (which you should) why not just install a 15A circuit breaker in the panel and run a new 120V , 15A circuit. It's not much additional work and you will have another 120V circuit in the shop and you can use it to power your control circuit for your compressor.

Ted
 
3Dogs said:
Those transformers are surprisingly expensive.
If you can run a neutral for less money, do that.
Click to expand...
I guess you are right.
I bought a used one from a local guy for $20 so not too bad.
There are a bunch of used ones on ebay.
I didn't look at them all.
I put the transformer and an outlet in a plastic enclosure box on the underside of the saw.

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What is the search term for that on ebay? Is it a wye transformer?
 
talvare said:
If you're going to run a neutral from your main panel (which you should) why not just install a 15A circuit breaker in the panel and run a new 120V , 15A circuit. It's not much additional work and you will have another 120V circuit in the shop and you can use it to power your control circuit for your compressor.

Ted
Click to expand...

That's what I would do, but I'd be concerned that the disconnect for the compressor wouldn't completely de-energize it. If some needed to do maintenance on the compressor motor or control and didn't shut the control breaker off, there would still be a live circuit after the main disconnect was deactivated.
 
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