220v wiring for a plasma cutter

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Old 05-09-16, 12:30 PM
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220v wiring for a plasma cutter

Hi everyone. I have a 100A service in my garage with a three-prong 220v drier outlets. Here's a pic:

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From my research and inspection, this appears to be a legacy NEMA 3-wire, 10-30, 220v/30A outlet. I just bought a 220v/30A plasma cutter, but the plug is a L6-30. Here's the pic:

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Questions:
1) Can I simply buy or make an adapter?
2) Can I change out the outlet to be an L6-30 using the existing wiring?

Thanks for your help!

Bob
 

Last edited by bcrimmins; 05-09-16 at 12:46 PM.
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Old 05-09-16, 01:44 PM
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You can either swap out the dryer receptacle for the locking 6-30 receptacle or change the plug (cord cap) on the plasma cutter to match the dryer receptacle. Swapping the cord cap is probably cheaper as the locking receptacle is probably about $40. The cord cap is more in the $10 range.
 
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Old 05-09-16, 01:45 PM
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A three prong dryer receptacle does not have a ground unless it is part of a complete metal conduit system. You need a ground for safety. You could get it to work but it wouldn't be code.
 
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Old 05-09-16, 02:47 PM
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Thanks ibpooks and ray2047. The box isn't grounded by conduit but there is a fourth ground wire (bare) in the romex leading to the box. The ground wire is not connected to anything, not if the receptacle plate. However, I have confirmed that the ground is hooked to ground in the panel. As far as I can tell, the L6-30 receptacles that I've seen only have three wire lugs, i.e., black, red, white. White is neutral, right? So there wouldn't be a way to ground a L6-30?
 
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Old 05-09-16, 02:56 PM
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Cap off the white wire. The black and red connect to the X and Y terminals on the receptacle. The bare connects to the green G terminal.
 
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Old 05-09-16, 02:56 PM
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As far as I can tell, the L6-30 receptacles that I've seen only have three wire lugs, i.e., black, red, white.
L6-30 should have 2 hot wires and 1 ground wire; 1 Blk, 1 Red and 1 Grn or bare.
 
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Old 05-09-16, 04:16 PM
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Do you plan to abandon the electric dryer? You are not trying to use the same receptacle for both the dryer and cutter are you?
 
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Old 05-09-16, 04:23 PM
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There's no dryer. I had the garage rewired about 10 years ago and had the electrician add a couple of 220 outlets just in case I ever needed one. Until now, I never needed one. Back then, I didn't know what type of outlet I'd need so I just told him to make them whatever he thought was useful. Turns out a dryer outlet isn't gonna be very useful.
 
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Old 05-09-16, 04:46 PM
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Turns out a dryer outlet isn't gonna be very useful.
But the cable is useful and a good job of planning ahead.
 
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Old 05-09-16, 05:01 PM
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Yeah, I figured the incremental cost of having a couple extra lines run was pretty simple math, even if I wasn't sure how I'd use it. Now, for about 40 bucks, I can adapt to my new plasma cutter.
 
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Old 05-09-16, 05:15 PM
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Turns out a dryer outlet isn't gonna be very useful.
And he used the wrong receptacle for current code.
 
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Old 05-09-16, 06:22 PM
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And he used the wrong receptacle for current code.
Since the re-wiring was done some ten years ago AND it is possible his jurisdiction is a couple of code cycles late, it is possible the NEMA 10-30 receptacle did meet current code at the time of installation. No matter since it is being upgraded to current code and usage for this project.
 
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Old 05-10-16, 02:30 PM
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Thanks, CasualJoe, for explaining that I need to cap off the neutral wire and instead use the ground wire. All the wiring diagrams I see are just as you described. As a layman, it feels odd to cap off a wire that was previously used to deliver 220v current... while still delivering 220v. I understand enough to "get" that there are different types of 220v service but not enough know the difference. Is there a way to simply articulate what the effect is of shopping out the neutral wire for a ground?
 
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Old 05-10-16, 02:47 PM
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I'm a layman of sorts. The difference between appliances using a bare ground or an insulated neutral depends on how they were wired:

A plasma cutter for instance uses straight 240 Volts

A Dryer or an Electric Range usually requires 240 Volts, plus 120 volts for clocks and such. The 120 volt portion must run back on an insulated neutral.
 
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Old 05-10-16, 02:49 PM
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The black and red deliver 240V. The white wire is only used for 120V. Electric cloths dryers use both 240V and 120V therefore need all three wires. Plasma cutters, welders, table saws and similar tools use only 240V and therefore only need the black and red.

Nowdays all circuits also require the ground for additional safety. Prior to the 1996 electric code cloths dryers did not require the ground which explains why the bare wire was not connected to the old style three prong dryer outlet.
 
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Old 05-10-16, 03:35 PM
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Thanks HandyOne and ibpooks, great explanation. I think I just felt one of the lobes in my brain swell just a little.
 
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Old 05-10-16, 04:06 PM
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And he used the wrong receptacle for current code.

Since the re-wiring was done some ten years ago AND it is possible his jurisdiction is a couple of code cycles late, it is possible the NEMA 10-30 receptacle did meet current code at the time of installation. No matter since it is being upgraded to current code and usage for this project.
Very true, we have no way of knowing what code was in effect 10 years ago in this particular town/city. That being said, 10 years ago would have been approximately 2006 when the electrician installed the 3-wire dryer receptacle. The NEC changed to require 4-wire range and dryer receptacles in 1996, 20 years ago. It would be interesting to know what code was in affect when the OP's dryer receptacle was installed. I have seen quite a few new 3-wire range and dryer circuits installed by DIYers, but never inspected.
 
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