12

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?

JRE
  • 418
  • 2
  • 9
Matt T.
  • 139
  • 1
  • 3
  • 5
    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 Apr 30 '22 at 12:39
  • 10x2 would not be safe. – Gil Apr 30 '22 at 16:04
  • 2
    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 Apr 30 '22 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 May 01 '22 at 01:55
  • 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! – user253751 May 02 '22 at 10:43

2 Answers2

17

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

enter image description here

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).

Harper - Reinstate Monica
  • 276,940
  • 24
  • 257
  • 671
  • 1
    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 Apr 30 '22 at 18:28
  • 2
    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 Apr 30 '22 at 19:47
  • 4
    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 Apr 30 '22 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... May 01 '22 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. – Harper - Reinstate Monica May 01 '22 at 18:40
  • @ Harper the plasma cutter I rewired and the wire feeds came with a cord and as I mentioned I cut the cord and put a pin and sleeve 30 amp as that was the plant standard (30 or 60 for portable equipment) – Ed Beal May 01 '22 at 22:26
  • I would not be surprised to find welders using a NEMA 10 plug wired for Hot-Hot-Ground. – Joshua May 02 '22 at 03:14
  • @EdBeal brown+blue+yellow/green are the mandatory wire colours for anything sold in the EU. Perhaps the manufacturer just didn't bother using two different kinds of cordage for the EU and US markets, or the US doesn't care too much about wire colours in factory-made molded cords, or something. – TooTea May 02 '22 at 08:01
  • @TooTea in the US, brown is legal for hot and yellow/green is one of the 2 legal colors for earth. Light blue is not a legal neutral color in building wiring but I believe UL will approve equipment with a light blue neutral. And GATT treaties might have had something to do with that. No question that Ed's right, I should mention it. – Harper - Reinstate Monica May 02 '22 at 19:18
10

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.

Ed Beal
  • 101,306
  • 4
  • 72
  • 150