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My plasma cutter has a 3 prong 220V power cord.

I want to make an extension cable that I can plug into my dryer's 4 prong 220V outlet.

I have a 3 prong receptacle to put on the other end of my cord for the cutter. I have 3 conductor wire - two hots, a neutral, and a ground.

Can I wire this as a 2 conductor and just leave off the ground?

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    You need the ground as well as both hots. You don't need the 4-wire dryer's neutral, so just leave that terminal on your extension cord plug not connected. Hopefully your plasma cutter is using a proper hot-hot-ground plug now, like NEMA-6, not an improper NEMA-10
    – Ecnerwal
    Commented Apr 30, 2022 at 12:39
  • 10x2 would not be safe.
    – Gil
    Commented Apr 30, 2022 at 16:04
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    But even if safe, a DIY cord won’t be UL certified, so I’m assuming if e.g. if the cord caused a fire or personal injury, OP’s insurance company may refuse to pay on those grounds? IANAL but I’ve heard it said that this is a risk of using DIY electronics.
    – bob
    Commented Apr 30, 2022 at 16:38
  • @bob if you hacked some parts together you could be right but, using listed cord caps or replacement plugs that are listed they are 100% code legal, the toughest example in the US is for hospital equipment. Normally a bad plug requires a complete replacement,,, unless it is replaced with a listed replacement, green dot and or “green stamp stating hospital grade” ok you don’t want to pay ~22$ for a simple 15 amp plug because it has a green stamp , but it is totally code compliant and OSHA approved when using the appropriate listed plug. NOTE purchase from a brick and mortar store BC on line ?
    – Ed Beal
    Commented May 1, 2022 at 1:55
  • does the plasma cutter have 2x hot + neutral, or 2x hot + ground? Generally speaking, if an appliance doesn't have a connection for ground then obviously you don't need to connect it. But you should never wire neutral as ground if there's any possible way to avoid it! Commented May 2, 2022 at 10:43

2 Answers 2

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What Ed Beal says, but let me backfill some details.

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Here is our cast of characters.

If you're confused about neutral and ground, perhaps it's the welder has a NEMA 10 connector. (Hot hot neutral). This was the standard dryer plug in the old days before safety was important.

For some strange reason a lot of people still use NEMA 10 plugs on welders.

Anyway, if your welder has a NEMA 10 plug, change it to a NEMA 6 plug (Hot-hot-ground) which is on the same shelf 2 bins over. Welders need ground if you don't like being dead.

Now it is a simple matter of getting “cordage” which is special flexible cable made for daily flexing - well you know, every one of your home appliances has cordage. Don't use Romex for this, it's not made to flex and will quickly get metal fatigue, crack, heat up, arc and start a fire.

You need 3-wire, which will be black white green wire colors. Here's the important part: mark the white wire black on both ends. It will not be used as neutral, but rather as second hot. (the two hots are interchangeable, you can use red if you want but it doesn't matter).

Also note that in European style cords, ground is yellow/green, hot1 is brown, and hot2 is light blue. (well they call that last one neutral, but in a North American context it's hot2 because of split-phase).

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    FYI , it is possible that the cord could be brown blue green or green with a yellow stripe. I found this on some “small” wire feeds and a plasma cutter, yes name brands sold in the US molded plugs that I changed to pin and sleeve 30 amp in my last job.
    – Ed Beal
    Commented Apr 30, 2022 at 18:28
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    I'm a fan of red for the re-mark to hot, - either works, (or any other "hot" color, for that matter) but red is more obviously an intentional re-mark, I think.
    – Ecnerwal
    Commented Apr 30, 2022 at 19:47
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    If the 10-30 looks like a Munch the 6-30 looks like Calvin and Hobbes' mom at the end of a long day of enduring his demands.
    – jay613
    Commented Apr 30, 2022 at 21:51
  • "Now it is a simple matter of getting “cordage”" To be specific, the type of cord OP wants for an extension like this would be 10/2 SJOOW (SOOW, SEOOW, SJEOOW also OK).
    – J...
    Commented May 1, 2022 at 18:32
  • @EdBeal Interesting. Yeah I was assuming OP would go into an electrical supply and buy cordage-by-the-foot, but you're absolutely right, OP could buy a pre-made 6-30 extension cord and lop off the plug and change it to 14-30. Commented May 1, 2022 at 18:40
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Ok, your plasma cutter is 220, well I will update you and say 240 as some like the modern voltage standards.

So you can use a 3 conductor cord, 2 current carrying conductors and the ground.

As someone else mentioned a 10awg cord is needed as dryers are 30 amp.

You do not need the neutral for your plasma cutter but you do need the ground.

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