240 Volt Wiring

rukoOctober 26, 2010

I recently purchased a 240 volt mig welder. It has a three wire cord, two black(hot) and one yellow-green ground. I read somewhere all new 240 volt appliances have to have a four wire hook up. Two hot, a neutral and a ground. I guess the welder is not considered an appliance. Anyway my barn where the welder is going does not have a ground wire going back to the main panel in the garage. It has two #8 hot wires for 240 volt, and a neutral for 120. I found two copper ground stakes used for the system ground. All outlets are GFI protected and grounded to the stakes. I know you shall NOT use the neutral as a ground even though they are electrically connected at the main panel.

My question is whether or not this is a safe system to run my welder? Should I get 240 volt GFI protection for the welder? I assume there is such a thing. Should I run a separate ground wire back to the garage panel?

Thanks

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Ron Natalie

No, there is no such requirement. The requirement was that certain items (ranges and dryers) were allowed to be grounded by a current-carrying grounded conductor which is no longer allowed. Your welder has two non-grounded current-carrying conductors and one equipment grounding (non-current carrying) conductor.

As for the wiring for your barn, as long as there are no other metallic connections (phone, cable TV, etc...) between your barn and what is feeding power to it, it probably is in compliance with the codes form when it was built.

There are 240 GFCIs but I'm not sure I'd want to run my welder on one.

    Bookmark   October 26, 2010 at 8:36PM
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smithy123

personally, i would run a ground back to the panel. you will also need to intall a ground busbar. i would never run a welder off a gfi!
or put in a qo panel. just kidding!

    Bookmark   October 26, 2010 at 8:53PM
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petey_racer

Smithy is wrong once again. You DO NOT need to run a ground back to the panel.

You have a 3-wire feeder where the neutral is also serving as the ground, just like the main service in your house. Since this is a detached structure this was allowed for many years.

Like Ron said, your welder is a 240v appliance, NOT a 120/240v appliance like a range or dryer. Your welder does not have, does not need and does not want a neutral.

    Bookmark   October 27, 2010 at 7:17AM
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weedmeister

When you said, "I found two copper grounding stakes", did you mean that you found the separate grounding rods for the barn? and that the subpanel in the barn (assuming there is one) is tied to these stakes?

    Bookmark   October 27, 2010 at 10:21AM
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smithy123

i said i would personally run a ground back 2 the panel, NOT THAT IT IS REQUIRED, nor menton anything about the codes.

    Bookmark   October 27, 2010 at 9:38PM
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ruko

To Weedmeister

Yes I found the stakes by/for the barn and there is a panel in the barn. The two stakes are connected to the panel's grounding lug with perhaps #8 wire or larger. The neutral coming from the main panel in the garage is also connected to this lug.

Thanks

    Bookmark   October 30, 2010 at 1:00AM
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brickeyee

The grounding electrode system is not for personnel safety, but lightning and distribution transformer leakage.

It has nothing to do with the grounding conductor (other than sharing the bar in a panel).

    Bookmark   October 30, 2010 at 8:43AM
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ruko

Brickeyee

I thought personal safety was one of the main reasons for grounding.

I copied this poor grammar and misspellings blurb from a site about grounding and it's function:

"Grounding operation in electrical distribution network:

The main reason why grounding is used in electrical distribution network is the safety: when all metallic parts in electrical equipments are grounded then if the insulation inside the equipments fails there are no dangerous voltages present in the equipment case. Then the live wire touches the grounded case then the circuit is effectively shorted and fuse will immediatly blow. When the fuse is blown then the dangerous voltages are away.

The safety is the primary function of grounding. Grounding systems are designed so that they do provide the necessary safety functions. Grounding also have other functions in some applications but the safety should not be compromised in any case."

    Bookmark   October 30, 2010 at 10:17PM
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brickeyee

The groundING conductor provides protection, not the grounding electrode system.

The return for all the current coming into a service is the neutral the POCO supplies, the groundED conductor.

It is grounded again at the service to prevent high voltage (7,200 V) and lightning from propagatubg on the internal wiring of the structure.

At 120 V the earth is a very poor conductor, and if you touched the hot line standing with bare feet on the earth you would never approach the 10 A plus required to open a breaker.

    Bookmark   October 31, 2010 at 3:23PM
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brickeyee

"At 120 V the earth is a very poor conductor, and if you touched the hot line standing with bare feet on the earth you would never approach the 10 A plus required to open a breaker."

Should be 15 A of course (or higher).

    Bookmark   November 1, 2010 at 10:28AM
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ontariojer

Don't be so hasty!

Here is a link that might be useful: SquareD QO 10A breaker

    Bookmark   November 1, 2010 at 10:42AM
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smithy123

TOO BAD WE CANT WIRE WITH LAMPCORD. I WANT THAT BREAKER!!! IT WOULD BE GREAT FOR A RECEPTACLE FOR HOLIDAY LIGHTS. IWOULD SUPPOSE YOU WOULD USE THAT FOR A DOORBELL TRANSFORMER, THOUGH.

    Bookmark   November 1, 2010 at 4:28PM
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brickeyee

I have 1 amp and 2 amp breakers.

They are used in control wiring circuits.

The smallest normnally used in a residential setting is 15 A, since #14 is the smallest wire easily available in NM, MC, AC, etc.

If you hunt around you can get MC in smaller sizes (I have some in #22) but again, it is control system wiring.

    Bookmark   November 2, 2010 at 9:30AM
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smithy123

do those breakers fit in qo panels? are they legal to be used for branch circuts in resudential appliatioins? i want one!

    Bookmark   November 2, 2010 at 6:44PM
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brickeyee

"do those breakers fit in qo panels? "

No, and they are heads and tails above typical breakers for residential use.

They are rated for aircraft.

    Bookmark   November 2, 2010 at 8:12PM
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smithy123

can you show a pic?

    Bookmark   November 2, 2010 at 8:21PM
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brickeyee

They are made by Pottter-Brumfield and look like a toggle switch with a large switch enclosure.

They are around $30 a pop.

    Bookmark   November 3, 2010 at 6:03PM
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smithy123

the only ones i could find were the push type like what is on a plug strip

    Bookmark   November 3, 2010 at 9:39PM
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brickeyee

Look here.

Here is a link that might be useful: Potter Brumfield PB W31 Circuit Breaker

    Bookmark   November 4, 2010 at 9:18AM
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smithy123

they would work great for a plug strip

    Bookmark   November 4, 2010 at 3:33PM
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pharkus

... they do make a 10amp breaker that WILL fit a QO panel.

QO110

There is not a HOM110 (SquareD homeline single-pole 10A), I haven't investigated any other manufacturers.

    Bookmark   November 4, 2010 at 10:43PM
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brickeyee

"they would work great for a plug strip"

Except it is expensive.

Much cheaper rocker style breakers are available, and many plug strips use them.

    Bookmark   November 5, 2010 at 10:27AM
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smithy123

i found a rocker that is rated for 20a, lighted, and RoHs compliant.

    Bookmark   November 5, 2010 at 3:51PM
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pharkus

Congratulations. Would you like a medal?

    Bookmark   November 5, 2010 at 4:20PM
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smithy123

i found it on digikey

Here is a link that might be useful: 20a lighted rocker breaker

    Bookmark   November 5, 2010 at 5:29PM
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