Contactor wiring

[nate379]

I am going to put my air compressor in a back shed and would like to be able to turn it off in the garage vs walking out back.

The shed is going to have a small subpanel with 240v run to it run off the main which is in the garage.

I could turn off the breaker and kill juice to the shed, but there are going to be some lights/outlets in there so I can see that not working out so well.

What's the easiest/most logical way to wire in a contactor?

I have never used on with home wiring, just familar with automotive relays.

 

[mrb]

you need a 2 pole contactor rated for the hp of the motor on your compressor. Both hot wires supplying the compressor pass through it. You can get one with a 120vac coil, just supply it from a 120v circuit off the same subpanel and use a standard lightswitch to turn the contactor on and off. Is the shed attached to the garage or seperate?

How many hp is the compressor?

 

[Waterwelldude]

It's the same concept as the car relay. 2 wires for the coil, and two poles instead of one.
Run the 240 power to the comp. from the breaker. At the compressor before the pressure switch is where the contactor should be.
Take the power from the breaker go into the contactor, from the contactor to the pressure switch.

The coil in the contactor should be 120 volt. Put a simple light switch anywhere you find it easy to get to. Run the 120 wires to the contactor coil just as you would a light. You could even use one of the lines you ran for the compressor for your 120vac line, just use the switch to break the common for the coil.


Travis

 

[mrb]

You could even use one of the lines you ran for the compressor for your 120vac line, just use the switch to break the common for the coil.

Travis

that wouldnt be code, cant switch only the grounded conductor.

 

[Aceman]

If your air compressor is started using a pressure switch only, buy a contactor matching the motor horsepower and switch it like it was explained above.

If your air compressor uses a motor starter in conjunction with a pressure switch, switch only the control circuit. You can get away with a small relay in this case, rather than a full sized HP rated contactor.

Remember, if you tap off a large motor circuit for your contactor control power, you either need to run the full sized wire to the switch or you must fuse it down.

 

[mrb]

Remember, if you tap off a large motor circuit for your contactor control power, you either need to run the full sized wire to the switch or you must fuse it down.

I just thought of something...if the shed is detached from the garage, is there an issue of the 120v control circuit running back to the garage? I think theres a code issue somewhere with this....

 

[nate379]

The shed will be around 80ft from the garage.

I will have to run a UF or set of THHN wires for the 240v feed to the shed for sure of course. Now to control the contactor (switch will be in the garage) will I have to run 120v wire back to the garage for the switch?

 

[mrb]

how many HP is the compressor?

 

[Aceman]

I just thought of something...if the shed is detached from the garage, is there an issue of the 120v control circuit running back to the garage? I think theres a code issue somewhere with this....

I'm sure there is, but's it late, and I was feeling lenient.

Probably in art. 225 somewhere....

Time to go wireless, maybe?

 

[nate379]

3hp I believe. 15amps.

 

[ManCave]

Are the contactors sized by HP or amps?

 

[mrb]

3hp I believe. 15amps.

a 25amp fuji contactor will run you $28.50 from automationdirect, forgetting about potential NEC issue (i think there is a way to do this..think light in garage controlled from house with 3way when garage is detached and has subpanel) you could just run a 14/2 UF for the switch loop for the contactor.

 

[mrb]

to clarify, the contactor I mentioned SC-E05-xxxx has 3hp rating for single phase 240v operation

 

[mrb]

Are the contactors sized by HP or amps?

thats a very good point, the OP needs to pay attention to the HP rating of the contactor. if you just look at the amp rating (which is resistive load only) you will end up with an undersized contactor and end up burning up the contacts.

 

[nate379]

Might be just less *** pain to not worry about it. Shut the breaker when I leave town, otherwise just leave it on.

 

[mrb]

Might be just less *** pain to not worry about it. Shut the breaker when I leave town, otherwise just leave it on.

Doesnt seem like that big of a deal but if you leave it out, spend $15 and throw a 3/4in pvc conduit in the ground when you put your feeder in so you can pull some wires if you decide to add the contactor and switch later.

 

[nate379]

I'm a bit confused on the NEC issue with running the wire to/from the shed.... what exactly is the issue??

I could also just 2 wires to the shed. a 240v line just for the compressor and another 120v line for the lights. It'd end up costing less that way really. No contactor to deal with.

Is there anything that says I have to have a subpanel even? The breakers in the main would protect it.

The reason I want to shut it off is I'm not sure how the compressor will react to -30* temps.

 

[mrb]

the NEC issue is you can only have one feed to a building. ill try looking at it later, im too braindead tonight

 

[nate379]

I do appreicate it.

I'm obviously not an electrician though the only way I'm going to learn is to ask questions and by doing.

The last electrician that did work at the house.... I wouldn't trust putting up Christmas lights.

 

[mrb]

ok found the code section. I dont have a 2008 available at the moment, so this is from 2005

225.30(D) says "Additional feeders or branch circuits shall be permitted for different voltages, frequencies, or phases or for different uses, such as control of outside lighting from multiple locations."

so seems like it would be ok.

 

[nate379]

If I just ran 2 leads, 1 to run the compressor and 1 to run the lights, would that be legit?

I can downsize my 240v wire as well. I was figureing to run 10 guage, but for 15 amps, 12 guage would be fine... (I was told to upsize 1 for the distance)

Then I could run another 12 guage for a 15 amp 120v circuit. I just am going to put 2 or 4 flourscent lights and a couple outlets.

I was going to run a PVC conduit for my air line and run the UF cable in that same trench along side that conduit.


Quite honestly the electric codes and building codes aren't really taken serious hear, but I want to do it right of course.

 

[mrb]

If I just ran 2 leads, 1 to run the compressor and 1 to run the lights, would that be legit?

I can downsize my 240v wire as well. I was figureing to run 10 guage, but for 15 amps, 12 guage would be fine... (I was told to upsize 1 for the distance)

Then I could run another 12 guage for a 15 amp 120v circuit. I just am going to put 2 or 4 flourscent lights and a couple outlets.

I was going to run a PVC conduit for my air line and run the UF cable in that same trench along side that conduit.


Quite honestly the electric codes and building codes aren't really taken serious hear, but I want to do it right of course.

quick note about the codes, while they may not be taken seriously you will be liable for any injury or property damage for work not done to code. Theres an electrician in prison for killing a little girl for improperly wiring a garage (this was an extreme case as he used the ground in the romex as a switch traveller) and i personally saw an insurance company refuse to pay a high six figure claim due to wiring not to code that wasnt even connected to anything or related to the fire. Its easy enough to do the work to code, so do it.

You cant run the two circuits as you proposed, but you could run one for the compressor and a switched one for the lights for example.

 

[nate379]

In the end, I need a constant 120v for the lights and outlets and a switched 240v for the compressor.

By switched, I mean the ability to turn it off not regularly, but if I need to... which the breaker would work fine for that.

If I just run 1 240v line out there I will kill the lights when the compressor is off so I'll have to go to the garage and turn it on if I want to go out to the shed and need light.

 

[mrb]

well, you can have one feeder to a subpanel, or you could have your compressor circuit plus a switched light. NEC 225 is the section which prohibits more than one feeder to a building, and the section I posted is an exception that allows an additional feeder for a different purpose such as switched lighting (you can also use the exception for your contactor switch) I dont know any other legit way around it.

 

[ManCave]

If it was me I'd run a 12/2 (which is good for 20 amps) from the house breaker panel to the compressor and just flip the breaker when you don't want the compressor to run. I'd run another 12/2 or 14/2 for your lights. if you're worried about code, remove the wire for the compressor when you go to sell your house. easy to do if you run it inside of sched 40.

 

[nate379]

I am thinking of just running the 1 wire out there and shutting it all off if I need to. K.I.S.S. pretty much at this point.

 

[rinny_tin_tin]

I am going to put my air compressor in a back shed and would like to be able to turn it off in the garage vs walking out back.

The shed is going to have a small subpanel with 240v run to it run off the main which is in the garage.

I could turn off the breaker and kill juice to the shed, but there are going to be some lights/outlets in there so I can see that not working out so well.

What's the easiest/most logical way to wire in a contactor?

I have never used on with home wiring, just familar with automotive relays.

Run low-voltage (e.g.12VDC) off of a bell transformer to drive a contactor loctaed at the compressor.