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Installing a Dedicated Circuit for an Air Compressor in a Garage

January 5, 2008

Kathie asks:
We have a compressor that will not run on a standard 15 amp GFI outlet in our garage. Can we change it to a standard 20amp outlet and if so, do we need #12 wire or can we use #14. Believe all of it is #12 anyway, but not clear on codes for 20-25 amp outlets but need to change our existing ones somehow. I have had electronics, but no residential training or info.

Wayne Gilchrist says:
Hi Kathie – If you upgrade this circuit to 20 amps, make sure every wire that is on this circuit is #12 AWG. If it is already protected by a 15 amp breaker, chances are the wire is only #14 AWG.

As far as changing the GFCI receptacle to a standard receptacle, no you can’t do this. The National Electrical Code (NEC) requires the garage receptacles be GFCI protected.

What is happening? Is the compressor tripping the GFCI or the circuit breaker? Is your breaker box located in your garage?

Kathies replies:
Thanks Wayne.
The garage has its own box and the compressor is tripping the outside GFI, but also not getting the compressor started on the inside home and garage outlets and tripping the breakers. We do have one outlet in the area of the freezer in the house that will run it every time, so probably on the same circuit and probably also a 20 amp. My mistaken assumption that all outlets would still be 20 amp and lighting 15 amp. Since it is a manufactured home, not sure what gauge we have throughout.
Do all exterior outlets have to be 15 amp GFI’s by code?

Wayne Gilchrist replies:
The outside receptacles need to be 15 amps minimum. This is typically the smallest sized circuit we will install in a house.

It sounds like the compressor needs to be on a dedicated circuit. So, the quickest and easiest solution is to add a new receptacle on it’s own circuit just below the breaker box in the garage.

This is pretty simple to do. Go to your local home improvement store and get:
1 – single receptacle
1 – single receptacle cover
1 – single gang old work, remodel or cut-in box. The terms vary by what part of the country you are in and who you talk to, but they are all the same box.
1 – 20 amp circuit breaker
10′ – 12/2 NM cable (romex) with ground

Before you get started, I recommend turning off the power to the breaker box in the garage if possible. If you need to leave the breaker box live, be very careful.

After you have turned off the power, remove the breaker box cover. Once the cover is off, determined if the main power supply enters from the bottom or the top. If the power supply enters from the bottom, do not install the receptacle centered under your breaker box. I recommend installing the new receptacle centered between the breaker box and the floor (vertically) and off center between the studs (horizontally).

1. Start by cutting the hole for the receptacle box to the exact outer dimensions of the box.
2. Fish your cable down from the breaker box to the new opening.
3. Strip approximately 8 inches of the outer sheath of the cable off and push the wires into the box until approximately 1/2 inch of the sheath is in the box.
4. Install the box.
5. Connect the receptacle (bare copper to the ground screw, white wire to the silver screw and black wire to the brass screw).
6. Install the receptacle cover plate.
7. Strip the outer sheath off the cable in the breaker box leaving approximately 1/2 inch above the connector.
8. Connect the bare copper wire to the ground bar, then the white wire to the neutral bar.
9. Install the new breaker and connect the black wire to this.
10. Put the breaker box cover back on.
11. Turn the power back on to the breaker box.
12. Turn the power on to the new recepatacle and test.

I hope this helps. If you have more questions or need further assistance, please post in the comments section below. If anyone else has questions or needs help with a similar project, please post in the comment section below as well.

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6 Responses to “Installing a Dedicated Circuit for an Air Compressor in a Garage”

  1. Ronald Walston on March 16th, 2008 11:16 am

    I want to install a sub panel in my garage for a 240V 15Amp air compressor. My main box is located in my basement about a 100 feet from where I want to install the garage sub box and receptacle. My main box does not have room for any more breakers so how can I connect the 240V line to my main box without using a breaker?

  2. Ryan on May 30th, 2008 7:17 am

    Can anyone direct my attention to the National Electric Code were it discusses whether running conduit for 3 phase industrial equipment is appropriate?

  3. jake on June 10th, 2008 9:06 pm

    i have 220 volts circuit breaker in my grage and i want to run a line to 220 volt air compresssor als i want to run some electric plugs 110 volts from the same circiut can i do that and what i need to convert 220v circuit to 120 v power line

  4. Melissa on December 20th, 2008 9:20 am

    My new garage was wired 14-2 for outlets with 15 amp breakers by an electrician. There are three runs all with a gfi. Two of them keep tripping and now one run won’t work at all. I know some electricity and wondering if I should take out the gfi’s? The only working run will trip if there are two power tools plugged in. Should the outlets have been 12-2 with 20 amp breakers? I am at a loss right now. I’m hoping that the gfi’s are just bad. Can I only use one power tool at a time?

  5. live wire on February 1st, 2010 3:37 pm

    Wish I would have come across this when buy dad purchased a new air compressor. I’ll be sure to forward him this page though so he can set it up properly!

  6. John Kidwell (Army Man) on June 1st, 2011 12:44 pm

    I’m about to install a 220 volt system for an aircompressor in my garage.
    What gauge wire is recommended?