Air Compressor Shutoff?

[Tom M King]

I put the breaker box by the door.

[Michael Schuch]

If the compressor over heats and trips the breaker, do the lights go out? It probably wouldn't matter much, except at night, and if you were doing a stunt cut on a shaper or something.

The contactor coil would be on the same 120v circuit as the overhead lights. The compressor will be on a completely different 240v circuit with the rest of the machines. If the compressor blows a breaker all of the other machines on that circuit will loose power but the lights will stay on. The contactor isolates the 240v machine circuit from the 120v light circuit.

[Steve Mathews]

I got to build a dedicated woodworking shop in 2006. Commercial building permit, architectural and engineering... Every hard wired machine was required to have a disconnect within reach of the machine.

A disconnect at every machine appears to be a good practice. In this case there is a disconnect included with the pressure switch to shut off the power to the compressor.

As mentioned earlier I do like the idea of using a contactor and having it powered by one of the light circuits. It accomplished every concern I have.

[Malcolm McLeod]

A disconnect at every machine appears to be a good practice. ....

I don't keep the NEC as handy bedside reading, but I have been told eleventy-seven times that they want a lockable disconnect within 10ft or line-of-sight for any hard-wired electrical load in an industrial (commercial?) environment.

And now back to your regularly scheduled compressor thread...

[Steve Mathews]

I don't keep the NEC as handy bedside reading, but I have been told eleventy-seven times that they want a lockable disconnect within 10ft or line-of-sight for any hard-wired electrical load in an industrial (commercial?) environment.

And now back to your regularly scheduled compressor thread...

What THEY want and what's reasonable and correct do not always coincide.

[Maurice Mcmurry]

A switched light circuit that also turns on a big machine seems like a bad idea to me. Someone un-aware of that setup could end up in harms way. We have an inspector who try's to imagine scenarios. I imagine one, "Hey why isn't this guys compressor working?" "I don't know I will turn on the lights while your checking it out"

[Bill Dufour]

A five hp compressor on 120 volts/20 amps is too much load by itself. You need at least 30amps at 120 volts. And you say the wire run is too long to upgrade. Sounds to me like you will burn out that motor from voltage drop.
At the very least drop the pressure switch to 100 psi max.
Bill D

[Bill Dufour]

Does it freeze in your location. Will you need lighter pump oil in winter.
Bill D

[John K Jordan]

I use a contactor to control my 5hp dust collector because of the wireless remote. However I use a simpler method for my 5hp air compressor (both are in a sound-insulated closet)

As you know there is a real danger with leaving the compressor powered all the time - shops have been destroyed by fire when the cutoff switch failed - and it’s too easy to forget about a cutoff that’s out of sight. (I refuse to use a circuit breaker as a daily disconnect)

I bought this two-pole industrial motor disconnect switch, rated at 30 amps, been using it daily for 6 years.
https://www.amazon.com/gp/product/B002MPQ51O
I mounted it outside the closet the closet, accessible from the main shop. I colored the lever a bright color so I can see in a glance if it’s off from across the shop.

Since access to the closet to turn off valves and such requires going into another room, I also brought the air through the wall it to main shop. her I have a pressure gauge, the main cutoff valve, water separator. desiccant dryer, regulator, and plenum with three valves feeding air to three different zones in and outside the shop. This puts everything in easy reach (except for the tank condensation drain valve). I’ve posted a photo of this before.

Note when buying a switch from Amazon Leviton sells a cheaper 30 amp switch that is NOT suitable as a motor disconnect. I didn’t discover that until I bought one and read it on the switch.

JKJ

[Jim Becker]

A five hp compressor on 120 volts/20 amps is too much load by itself. You need at least 30amps at 120 volts. And you say the wire run is too long to upgrade. Sounds to me like you will burn out that motor from voltage drop.
At the very least drop the pressure switch to 100 psi max.
Bill D

The compressor is 240v. The 120v references is for the control side of a contactor. There's no load issue here.

[Curt Harms]

Similar to Maurice, a guy I work with had an air hose connection blow out on his 60 gal compressor when he was away for the weekend. His compressor ran for like 48 hours before he came home. As I understand it, the garage was pretty hot inside.

For that reason, I would have some type of emergency shutoff but I'm not sure what people typically use. Wiring the compressor with the lights seems like a neat idea.

So yeah, its a valid concern for sure.

Yup, and make sure the contactor fails unpowered, as I image nearly all do. If anything that should never happen does, you want the failure mode to be in the safest condition, in this case unpowered.

[Malcolm McLeod]

A switched light circuit that also turns on a big machine seems like a bad idea to me. Someone un-aware of that setup could end up in harms way. We have an inspector who try's to imagine scenarios. I imagine one, "Hey why isn't this guys compressor working?" "I don't know I will turn on the lights while your checking it out"

Certainly a safety consideration. In a home shop we'll each have to answer, "How safe does it need to be? How complex do we allow it to be?"

Put a contactor in the 240VAC power delivery to the compressor; drive the contactor's 120VAC coil off the light switch; compressor is dead when the lights are off. Then put a local 240VAC disconnect - clearly visible at the compressor. While Mutt goes to turn on the lights, Jeff can lock-out-tag-out the disconnect and only then check why the compressor isn't running. Safely.

We all have OSHA compliant LOTO stuff in the shop. Right? ( I don't, but I do yell at my wife not to touch anything.)

[Steve Mathews]

I was about to create a separate part 2 to this thread after having an idea to enhance my setup. But after reading member Jordan's post I thought it might be a good to continue with it here. First of all my enhancement idea ...

Along with having a contactor for the compressor motor energized by a lighting circuit, I was thinking of introducing an inline switch (120VAC) inside the shop and a simple light indicating that there is power in that line. This light is in addition to the shop light indication. Several days go by without using compressed air so it doesn't make sense to leave power going to the contactor. And if air is used I mostly get by with what is stored in the tank. If more is needed all I would have to do is flip the switch mentioned above and power is restored to energize the contactor. The same benefits as before apply except now there is an indication (light) that the compressor is set to operate automatically or not and it can be controlled inside the shop.

The switch mentioned by John sure makes it simpler and a lot less expensive. The only concern or question I have with it is will it reset automatically if power is interrupted and restored? I don't know if that's much of an issue with a compressor but possibly for some other machines. I would also have to ask, what is the functional difference between a contactor and this switch?

[Bill Dufour]

The compressor is 240v. The 120v references is for the control side of a contactor. There's no load issue here.

He said it is one the same circuit as other outlets. I take that to mean 120 volt outlets.
Bill D

[Malcolm McLeod]

He said it is one the same circuit as other outlets. I take that to mean 120 volt outlets.
Bill D

Mr. Dufour, at some point in the past - - I think it was you - - cautioned (me, et.al.) about offering electrical advice here. I AM a bit slow on the uptake, but I am beginning to understand.

I would encourage Mr. Mathews to consult an electrician; live and in person.