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Old 03-11-2009, 05:04 PM   #1
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Air compressor box with cooling fans


I am about to mount and wire my 240 volt air compressor in my shop. This thing is loud, so I plan to build a ventilated, sound proof box for it.

I want to have a fan or fans come on to ventilate the box whenever the compressor is running. At first I thought this was simple, but I'm less sure now. I'm not sure how to wire this to code, because the fans I want to install are 120 volt.

The pressure switch is a standard Square-D. It has one circuit for each leg. I *could* connect one leg to the fans, and then to the neutral (which would not be used by the compressor at all). I know it would work; the fans would run whenever the compressor runs. But... That means I'd be feeding, for example, a 2 amp fan with a 30 amp circuit breaker.

Am I correct that this will not pass code? How should I handle this?

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Old 03-11-2009, 05:09 PM   #2
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Air compressor box with cooling fans


What I would do is mount a box on the outside of the enclosure, attach a cord with strain relief connector to the box, and install a switch in that box.

But, I'm sure the sparkies who have actually done stuff like this will give much better information...this is just my opinion.

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Old 03-11-2009, 05:11 PM   #3
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Air compressor box with cooling fans


I would try and find a different source to feed the fans, an outlet nearby. I would not tap off one leg to feed the fans even with the low amps. You are correct, it is not code to do it this way. I am an electrician in your area if you need any answers email me.
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Old 03-11-2009, 05:23 PM   #4
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Air compressor box with cooling fans


Maybe replace the pressure switch with a 3-phase, triple pole model, and use the third pole for the fans?

Edit: That would mean a 240v circuit, and a 120v circuit coming into, and out of the single pressure switch... Hmmm?
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Old 03-11-2009, 08:05 PM   #5
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Air compressor box with cooling fans


If you put a fused disconnect switch on the fans, then you would be OK. Feed the switch with 10-2 from your compressor, then leave the switch to the fans with 12-2. Put 15 or 20 A fuses in the switch to protect the wiring and fans at the proper ampacity.
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Old 03-11-2009, 08:27 PM   #6
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That makes perfect sense. Thanks InPhase.
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Old 03-11-2009, 10:54 PM   #7
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Air compressor box with cooling fans


InPhases idea is pretty much standard. Not very expensive, meets code, and works.

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Old 03-11-2009, 11:01 PM   #8
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Air compressor box with cooling fans


Could always use an external relay mounted to a j-box, and use a low-current 120 volt tap off the pressure switch just to activate the relay, which would control the circuit for the fans.

Just a thought, won't the noise of the air compressor be heard through the fans? And how loud are these fans you plan on using? I have considered doing something like what you are proposing the air compressor I have, but haven't done it yet.
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Old 03-11-2009, 11:04 PM   #9
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Inphase actually has the best idea.
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Old 03-11-2009, 11:14 PM   #10
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Originally Posted by theatretch85 View Post
Just a thought, won't the noise of the air compressor be heard through the fans? And how loud are these fans you plan on using? I have considered doing something like what you are proposing the air compressor I have, but haven't done it yet.
You simply build a labyrinth for the air to flow through, and cover the walls of the labyrinth in foam so the sound is greatly muffled.

Here is a write up that illustrates the idea pretty well:
http://www.cianperez.com/Photo/Expos..._Enclosure.htm


I don't like fuses, so I think I'll just put in a two or four slot sub breaker panel fed from the compressor.

Last edited by gp_wa; 03-11-2009 at 11:32 PM.
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Old 03-12-2009, 06:40 AM   #11
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Air compressor box with cooling fans


i would just use an ambient temp thermostat and turn the fan(s) on with that once the temp in the box gets, let's say 80 degrees.

An attic fan that already has this set-up would be a simple solution.
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Old 03-12-2009, 07:49 AM   #12
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Air compressor box with cooling fans


Quote:
Originally Posted by gp_wa View Post
You simply build a labyrinth for the air to flow through, and cover the walls of the labyrinth in foam so the sound is greatly muffled.

Here is a write up that illustrates the idea pretty well:
http://www.cianperez.com/Photo/Expos..._Enclosure.htm


I don't like fuses, so I think I'll just put in a two or four slot sub breaker panel fed from the compressor.
Ah, that's not a bad looking design. I might have to look into building one of those enclosures, though I think I'd want to use a heavier cord than the 14/3!
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Old 03-12-2009, 10:37 AM   #13
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Air compressor box with cooling fans


I suppose you would have to be looking at an economical way to suppress the noise to even do this sound box thing. If the compressor is portable or fixed I'd look into making a compressor room inside or outside and pipe the air to a good quality hose reel like a reel craft. This of course becomes a cost thing but if you are using that compressor a lot you'll be happier I would think.

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