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Single phase 120v from 208 compressor circuit.

kineticmx

Aluminum
Joined
Mar 10, 2014
Location
United States, CT
Hi guys. Question pertaining to a step down transformer, and how you would wire it into an air compressor control for operation in conjunction with the air compressor.

I have a 5hp 208v 3ph Dresser air compressor. I run it off a dedicated 20A circuit(4 wires, 3ph + ground). I run a refrigerated drier after the compressor, which I currently plug in manually. I am also looking to put an auto drain on the compressor to help with condensation accumulating.

My goal is to flip one switch and turn everything on at once. Keep it idiot proof. The motor starter is obviously controlled by the pressure switch, so I could just put a double pole switch in series with the pressure switch.

Long winded, but do I need a transformer to step down from 208-120, because its definitely not up to code to go line - ground for the 110 circuit. Nor do I think its appropriate to pull another wire through the pipe for neutral, since it would be on a three pole breaker.

The easy answer would be run a dedicated circuit for the auxiliaries and put it into the double pole switch, but I dont have any more room in the panel to fit another circuit.

Any input appreciated.


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Have you checked to see if your air dryer can run on 220?

If not, you can pull the neutral and add a subpanel with a 3 pole and a single pole breaker. You will also need a disconnect.
 
I like the direction you're headed.
Just a thought - we did similar and set up our auto-drain with a normally open valve. When the air drier is energized (120V single phase) it closes the valve and the tank fills. When we shut the compressor off at night (we have low voltage switches at each exit that can energize / de-energize both circuits) the drain opens and dumps all of the air. If the air drier is functioning properly, there should be very little to no water, but if you've been around refrigerated air driers long enough, then you'll understand the if at the beginning of the sentence. The only downside to the low voltage setup is lockout / tag-out for air pressure has to be done via a local isolation valve at each machine that is hard-plumbed into the air supply, and you need a way to bleed off pressure at the machine (usually an air gun)
 
Thermite,
I appreciate the reiteration on not using circuit breaker as a switch. I was unclear in my original post. The pressure switch has an auto/off switch on it, thats how I control it right now. Not flipping the breaker.

The normally open drain valve would work however I think I will opt for a timer switch as sometimes the air system is pressurized for days on end. Needs to be drained during use.

I will look into a transformer otherwise pulling neutral and putting in a small sub panel might be most appropriate.


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