Wiring air compressor through wall switch?

I am going to put my 120v, 15A compressor in the back of my garage. I would like to control it's outlet with a wall switch near my entrance door. I was doing some research first, and found this post

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saying that motor powered appliances (specfically air compressors) should never be controlled by a wall switch. If I use a heavy duty

20A switch, is this ok? I am using a 20A breaker and 12g wire.



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I was doing some research first, and found this post

I don't know about that but here's something else to consider. When your compressor is switched off by the pressure controller it opens a valve that releases pressure from the head so that it can start more easily the next time. If you flip off the lever on that switch (assuming yours has one) it has the same effect.

I'm not sure but I believe that if you just kill power this won't happen so if you still have pressure on the head the next time you switch it on you will put a considerable bit of extra stress on the motor plus you'll probably pop the circuit breaker and of course that will give your wall switch an extra workout too.

Hopefully someone that knows more about it will chime in. :-)

Best Regards, Keith Marshall snipped-for-privacy@progressivelogic.com

"I'm not grown up enough to be so old!"

Reply to
Keith Marshall

You need a switch specifically rated for the HP of the motor you're switching.

Switch ampere ratings are all about lighting loads. Some of the more expensive borg-grade switches are HP rated as well. If you can find one, then Bob's your uncle.

You can also get the right switch (or contactor, if needed) from any of the industrial supply houses. Their catalogs usually have a bunch of application information.

Reply to
Charles Krug

I will get a lot of flames on this but yes "I" would. make sure the outlet is also rated at 20AMP to keep the NEC fanatics at bay.

If you cycle the switch 10 - 15 times a week while the compressor is running then you might only get 2 - 3 years of life out of the switch. The most common failure (if it fails) will be... it won't run. the other failure mode, that might happen in 1 out 50000 switches is... it won't shut off. In that case unplg the compressor and replace the switch in the morning.


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Find the beefiest switch you can find. My dad gave me his old 8" tablesaw with a 3/4 horse motor. He had wired a conventional switch inside a metal switchbox that was mounted on the saw (I guess the original had died). Anyway, I usually end up replacing the switch every few years since it gets fried and either wont turn on or wont turn off (about the same percentage). I use the red bodied "commercial" 20 amp switches from the Despot that cost about $3-$4 each. The saw is not used much but I'd guess maybe

500-1000 cycles between failures.

A compressor is usually 1 horse minimum so life will be shorter than what I have experienced (inductive motor loads are hell on switches). After saying that (and heeding the other advice about the compressor unloading) I'd say buy the switch that is rated for the highest current draw (at least 20 amps) and preferably has mercury wetted contacts. Expect to replace it every few years if switching on a low power compressor daily.


Reply to
Bruce Rowen

How do you spell "never"?? The start surge on that thing is probably close to 50 A! If you just have to do this, wire the power straight in and add a magnetic starter...Griz has them, among others. But, it's a lot of money. Why not just leave it on? If you don't have leaks it doesn't matter. Mine's been on for years. I crack the drain valve to keep the condensate from accumulating, so it runs once or twice a day to keep the pressure up.

If you don't use it often, just leave it off and start it five minutes before you need it.


Reply to
Wilson Lamb

You need a motor rated switch, and preferably one that has DPDT. Of course if you have a Mag starter you could wire up a remote pendant. Another route would be to use a relay setup.

Reply to
Steve Wilson

The other replies offer practical advice about the switch ratings and the unloader. As for the unloader you can get around that at worst if you switch off the compressor only after it has cycled off on its own.

But the code safety issue with a wall switch or any other remote switch is on account of the risk of the switch being turned on while you are working on the equipment. Particularly if the switch is out of sight of the equipment. So at worst anything remotely switched like that should still have a cord and plug you can unplug at the equipment, or a separate disconnect switch again at the equipment.


Reply to
Bob Powell

Bruce Rowen wrote in news: snipped-for-privacy@aoc.nrao.edu:

Not really. You're using your switch on your saw to start and stop the motor. He won't be doing that with his compressor. The pressure switch on the compressor will still serve that function. All he is doing is interrupting the power in the circuit. Provided that the compressor is not running, or that the tank is not bled below the pressure cutoff while the power is off, he will never be switching the power to a running (or starting ) motor. I have switched my compressor like this for lots of years while no failure of any switch.

Reply to
Secret Squirrel

another voice of practicality, thank you. If we were all high volume shops with multiple employees then this discussion would be different. We are, for the most part, amateurs that try and get to our shops 2 - 3 times a week. The MTBF for switchs, compressors.... falls off the chart with these usage rates. yes is you by the $0.43 switch it will probably fail in a year but it will also fail in the same time if you put it on your kitchen light.

BRuce (semi-amateur)

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That would be the ideal way to use the switch. Problem is though many people won't want to wait for the motor to stop before switching power off. ALso, unless the system is 100% air tight, the first switch-on in the morning will kick the motor on.

The _proper_ way to set this up is with a remote switch wired to a compressor contactor switch (has the bleed off mechanism), but the prices are not friendly. My compressor is accessible easily enough and I just use the switch installed on it (6 HP 60 gallon unit). If I was to make a remote switch I'd just use an old contactor switch designed for big motors If the HP was under 2 I'd just deal with replacing a good wall switch every so often or do what the Squirrel does and switch it only when the motor is not running.


Reply to
Bruce Rowen

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