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Electrical wiring can be a real challenge, especially if you know nothing about how it all works. This weekend I got to learn first hand how to set up and connect a 220v outlet for use with my brand new air compressor.

I was already familiar with normal 110v wiring and have completed several installations. However, my first attempt at wiring 220v yielded some shocking results, no, nobody was injured, or even shocked for that matter. But, let me tell you straight away, DO NOT Connect the red and black wires together, that does not create 220v. What it does do is pop your circuit breaker. This I learned by doing.

When wiring 220v there are two possible ways to wire up your receptacles. One way is with 4 wires and the other is with 3 wires. In my case I went out and bought a new air compressor. This compressor required wiring 220v on at least a 15amp circuit. It did not come with a plug end wired to it. And it had only 3 wires running from the motor.

In my garage I already had an existing 4 wires that were connected to a 15amp "ganged" double pole circuit breaker and routed along the garage door header and over to the corner, where they were left just hanging down the wall about 2 feet from the ceiling. Personally I really didn't like this unfinished circuit that the previous owners had left, but I didn't know how 220 worked and I didn't have anything to wire into it either.

Anyway, pictured below is my service panel and a second picture of my panel with the service cover removed. The double breaker I used for this installation is the one on the upper left, the black wire goes to one terminal and the red wire to the other. Of course ground and common go to the bus bar (upper right in the picture).

Garage Breaker Panel

Garage Breaker Panel (Service Access)

NOTE: When connecting wires of different colors (e.g. in the picture above a blue wire was used for a ground, see how it has been marked with green electrical tape to avoid confusion.) be sure to mark wire substitutions appropriately with electrical tape in the colors they should represent.

In order to make this work for my application I needed to extend the wires further down the garage wall and then attach and wire in a box and receptacle. I also would need to install a plug end on the compressor's 10’ cord. So, off to the local hardware store where I bought some grey pvc conduit, a 90 degree bend, a 90 degree splicing box, a receptacle box, a cover plate, and a 250v 3 wire receptacle, 4' of red wire & plug end.

There are several styles of 220v receptacles available depending on what you are going to run with it. Below is a picture of the style that I used.

Singel 220v Receptacle

It is important to note that your wires should be no smaller than 12 gauge. I used 10 gauge wire for this application. (10 guage wire is heavier than 12 guage wire, 8 guage is heavier than 10 guage and so on)

How 220v works with 4 wires: (one wire to each)
1 Black wire carries 110v
1 Red wire carries 110v
1 White wire acts as a common
1 Green wire acts as a ground

How 220v works with a 3 wires:
1 Black wire carries 110v
1 Red/White wire carries 110v (if you use white flag it with red electrical tape)
1 Green wire acts as a ground/common

(If you have 4 wires in the wall, but you are wiring them to a 3 prong receptacle, connect the green wire to the green "ground" screw on the receptacle or if no ground screw is present, attach this wire to one of the receptacle mounting screws. That way if the common fails, you still have the added protection of a ground)

In order to save some money and time, I decided I didn’t need a 10’ cord on my air compressor, so I cut off and used 4’ of the cord to extend my wires down to the receptacle. I slit the 4' section of cord and pulled the wires out first (black, white, green)

Because I already had 4 wires coming from the panel I extended them as follows: I attached green to green (ground), black to black (110v), red to red (110v) and white to white (common)Then attached them to the receptacle. My receptacle did not have a ground screw so, I attached green to the mounting screw between the receptacle and the plastic box.

Once the wiring was complete, a volt meter was used to test the voltage at the receptacle. Mine read in at 239v, which is normal. So with the receptacle installation complete, that only left the plug end to be installed on the compressor’s cord. This was a very straight forward process of connecting 3 wires to 3 terminals and the extra ground wire to the receptacle mount. Once complete all ran beautifully.

IMPORTANT NOTE: Never, I mean NEVER run romex wire through electrical conduits. It will overheat, melt, and possibly cause a short or a fire! Not even through just 3 feet of PVC conduit. I have seen it in my own garage and it is a real danger. I have pulled apart 3-4' lengths of PVC conduit and found half melted romex right at the breaker box. It is against building code and it is just plain wrong. If you are running conduit, use individual wires.

220v Receptacle in Box
Pictured above is the finished installed outlet . . . not much to look at, but I'm proud of it. If you found this article helpful, please consider voting for it.

DISCLAIMER: IF YOU DO NOT UNDERSTAND OR ARE NOT FAMILIAR WITH THE TERMS AND IDEATIONS DEPICTED IN THIS ARTICLE. DO NOT ATTEMPT TO WIRE YOUR OWN 220 VOLT CIRCUIT. CALL IN A PROFESSIONAL, OR SOMEONE WHO IS FAMILIAR WITH THIS PROCESS. MISTAKES WITH ELECTRICITY CAN CAUSE SEVERE INJURY AND SOMETIMES DEATH.

FreeCracker4Jack

Last Updated: 6/30/2008