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Thread: Extension cord for 220V

  1. #1
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    Extension cord for 220V

    I have been advised that using an extension cord on my 220V air compressor would be dangerous. Right now I have it plugged directly into the wall source but would like to move it to a different location in my garage. Would using an extension cord be inviting trouble?

  2. #2
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    If you keep the cord short (<10'), you'll be fine with a large-gauge wire... it's no different than running an extra 10' of Romex to the outlet. I use a 9' extension for my DC, I think it's 12-AWG.
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  3. #3
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    I make my own extension cords for 220v machines. It's quite simple and fairly cheap. As Dan wrote, keep it relatively short and use a 12/3 wire with the proper plug.
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  4. #4
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    There's no problem with using an extension cord, however before you go out and buy #12AWG wire, make sure it's the correct size.

    You may only need 14 gauge, in which 12 AWG is fine, however if you need #10 AWG the #12 isn't any good.

    What is the current rating of your compressor?

    Regard, Rod

  5. #5
    My well pump runs on a cord that is over 300' long, and it's 220. As long as cord is properly sized, anything less than 50' should be fine. After 50' step up to the next wire size.

  6. #6
    The Lowes in my area has lots of 220 v extensions already made up, and the prices were cheaper than what I would have had to buy separately.

  7. #7
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    Bear in mind that you can use a smaller diameter (higher number) wire with a machine running on 220v compared with the same machine running on 110v. There is a tendency to think that with higher voltage a larger diameter wire is needed, however just the opposite is true. This is because the power converted into heat in the wire is proportional to the square of the current flowing through the wire, and the current needed to run a machine of a given power will be only half as much with 220v compared with 110v. It is the current converted to heat by the resistance of the copper which is dangerous and can melt the wire and cause a fire.

  8. #8
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    An auto paint supply dealer who sold me my compressor advised against a 220v extension cord. They are sold by Home Depot and such places, but are usually 12-feet or less. I have one of the shorties, and use it at times with my 4HP 220v compressor. It does get warm to the touch if I'm putting a heavy demand on the compressor.

    Along this line of thought, in California it is against the electrical code to have two separate 220 machines plugged into the same circuit simultaneously. Either one machine at a time, or a dedicated 220 circuit per machine. I believe the electrical code is now uniform throughout the country.

  9. #9
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    Quote Originally Posted by Gary Curtis View Post
    An auto paint supply dealer who sold me my compressor advised against a 220v extension cord. They are sold by Home Depot and such places, but are usually 12-feet or less. I have one of the shorties, and use it at times with my 4HP 220v compressor. It does get warm to the touch if I'm putting a heavy demand on the compressor.

    Along this line of thought, in California it is against the electrical code to have two separate 220 machines plugged into the same circuit simultaneously. Either one machine at a time, or a dedicated 220 circuit per machine. I believe the electrical code is now uniform throughout the country.
    the national code aside, any circuit that got more than three or four of appliances [lamps or radio included] run a risk of overuse, watch your light bulbs flicker when a machine starts up

  10. #10
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    Any electric motor can be run on an extension cord, as long as the copper wire is of sufficient size to prevent voltage loss.

    You cannot, however, choose wire size without knowing the size of the compressor's motor and how long the cord is to be.

    Let's take my 5HP Ingersoll-Rand, with a nameplate rating of 22A at 240V. With 10ga wire and a "1/2 total circuit length" of 100 feet there is a 2.2% voltage drop, within the 3% guideline for induction motors. What that means is that if I have my 30A breaker wired with 10 ga wire and there's 50' of wiring between the breaker and the outlet, I have 50 ft (100 - 50) of extension cord I can use and stay at ~2% voltage drop.

    If I knew in advance I needed a long cord and used 8ga the "1/2 total circiot length" at 150' is 2.1%, still within the 3%. With the same 30' breaker and the same 50' to the outlet, I could use 100' of cord at stay within my 3%, as long as 8ga was used all the way from the breaker to the compressor.

    Jim
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  11. There is a lot of misconception about extension cords because they have been historically misused so much. Contrary to popular belief, the primary voltage drop on a properly sized extension cord does not happen as much with a moderate length (not supper long), but at the plugs, especially the female plug. The resistance per foot of the cord is no different than the same size wire in romex. In other words, it makes no difference whether your circuit uses an extra 25 feet of cord versus an extra 25 feet of romex. What is different is that you have an extra compression fitting in the middle.

    Adding to this is that typically the lighter the cord (or the longer its length for the respective cost) the cheaper the plugs they put on the ends. The cheap female end is the most prone to increased voltage drop because heating in the cord can loosen the compression between the blades.

    Don't get me wrong. I don't advocate the use of extension cords. But when the cord is properly sized, it is not much difference between supper short and moderately short. The cord ends are of greater concern.

  12. #12
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    Thanks all to your replies to my question. My compressor must be at least 25 years old and at the time I added the 220V circuit to my garage I also made up a 25-foot extension cord. Over the years, I've never had a need to use it but I might in the very near future. I could always reduce the length of that cord too. It is a flexible cord so I assume I had the info at the time to use stranded wire. I'm still rearranging things in my garage so I won't be making any changes immediately.

  13. #13
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    Quote Originally Posted by Charles Bjorgen View Post
    It is a flexible cord so I assume I had the info at the time to use stranded wire.
    This is correct... solid wire should only be used behind the wall.
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  14. #14
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    Somebody here said there was no difference in the effect of a specific size wire, regardless if the length were extension cord or Romex. Typically, housing or shop wiring is single strand solid copper. And, for the sake of flexibility, extension cords are stranded wire.

    If you have the same size ( say 10 awg), is the voltage drop the same for 20 feet of each?

  15. Quote Originally Posted by Gary Curtis View Post
    If you have the same size ( say 10 awg), is the voltage drop the same for 20 feet of each?
    Yes. Within reasonable limits, the resistance per foot is the same for either type.

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