Installing a Dedicated Circuit for an Air Compressor in a Garage
January 5, 2008
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?
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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