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AssuredElectrical , Master Electrician
Category: Electrical
Satisfied Customers: 4241
Experience:  Contractor-42+ Years in the ElectricalTrade
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Hi there, I would like to run a switching circuit to control

Resolved Question:

Hi there,

I would like to run a switching circuit to control a 30A/220V outlet. (I am putting a shop in my basement, and would like to control a dust collector in the garage.) Based on my research, it looks like I can do this using either a standard 110V circuit, or go low voltage (24V). I've found power contactors that can take either as input.

I have two questions:
1) Is there any reason to pick one route over the other? It seems that low voltage is more common, but I don't see what it does for me other than add the expense of a transformer.

2) If I did use the transformer, am I restricted in where I can install it within a finished space? (I'm used to seeing doorbell transformers left exposed in an unfinished area of the basement.) Can I install the transformer in a metal electrical box and just put a cover on it, or does it need more venting than that?

Thanks in advance!

Submitted: 2 years ago.
Category: Electrical
Expert:  AssuredElectrical replied 2 years ago.

AssuredElectrical :

Welcome. My name is XXXXX XXXXX would be glad to assist.

AssuredElectrical :

Personally, I would use a standard 120 volt coil contactor. No reason or benefit using a low voltage and just adds to expense and equipment that can fail.

AssuredElectrical :

The dust collector probably is a little high in current to use a small relay, and I would suggest a lighting style contactor to control the power.

AssuredElectrical :

We do this is child care/adult care environments, connecting the stoves through a contactor, so that when the fire system is initiated, it turns off power. Yours would be a little different as you are turning it on when something else takes place.

AssuredElectrical :

What you want to do is this: Run your 220 volts with ground from the circuit breaker to a box large enough to house the contactor. Then from the contactor to the receptacle for the dust collector. Then run your 120 volts to your control and to the contactor coil. So, when you apply 120 volts to the contactor, it makes and turns on power to the dust collector. I dont know what you are using to control the coil on the contactor, but it just needs to make and break the hot wire, neutral would connect straight through to the coil

AssuredElectrical :

Full Size Image

Expert:  AssuredElectrical replied 2 years ago.
A contactor similar to this one with 120 volt coil--CLICK HERE

Just reply for any clarification or additional info,
Customer: replied 2 years ago.



First of all, thank you so much for your fast (and helpful) response! Wow! Even with a figure! I'm very grateful for the thoroughness of your reply, so thank you for that.


FYI, although I saw your reply shortly after it came in, the web browser I am using at work is ancient and would not let me type a reply.




I appreciate the confirmation that there's nothing wrong with using standard 110/120V to power the contactor coil. Every resource I've seen that discusses what I'm trying to do talks about stepping down the voltage and using thermostat wire, but I didn't see the point. As you said, more expense and more chance for failure.


Only two minor things left. I'm assuming the inspector will want a "means of disconnect" near the receptacle, so I was intending to purchase a small shutoff box and install it between the breaker panel and the contactor. Do you think that's unnecessary? Something like:


Last thing, you suggested a lighting style contactor. Is there something that makes it more appropriate than other styles of contactors? I was originally intending to get one of the following:


Thank you so much again for your help. I really appreciate it. (I would submit the rating now, but I wasn't sure if that would close the question out and prevent my reply from going though. :)





Expert:  AssuredElectrical replied 2 years ago.
I understand on the ability of reply, some of the browsers in their different versions do not work well with live chat.

On the contactor, I would suggest the Eaton C25BNB240A over the other. Rating is good for application and should give a good longevity as their products are very good.

On the disconnect, you could use that one, or just install a plain 20 amp double pole switch to use. If the circuit is going to be 30 amps, they make a 30a double pole as well.

Now, if the breaker panel is in a line of sight of the contactor, you do not need the shutoff between, but if not, I would just use the switch for working on the contactor.

The dust collector, if plugged into a receptacle, does not need any cutoff itself, as the plug and cord is allowed by code for it to be the disconnect on maintenance.

Let me know if anything else is needed.

AssuredElectrical, Master Electrician
Category: Electrical
Satisfied Customers: 4241
Experience: Contractor-42+ Years in the ElectricalTrade
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