Wiring for Welder

noworriesDecember 7, 2004

I'm wiring my garage and want to install two outlets for a welder that I would then move between them as the need arises. Do you typically put two 50 amp breakers in the panel and have separate circuits, or use one and tap the line in a splice box to feed the second outlet? I've only got 100 amps coming into the building.

My local inspector doesn't like the idea of two outlets on a single 50 amp circuit. My opinion is that its safer to trip the single 50 amp breaker if I were stupid enough to connect two big loads at once, than otherwise to rely on tripping the main breaker with a panel overload.

I posted this issue on the wiring forum, but it occurs to me that this group may have more real world experience with this particular issue. (There doesn't seem to be a problem with tapping the line WRT the national electric code).

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I am not a electrician, but what you are planning does not sound unsafe,compare it to a 20 Amp kitchen circuit that has multiple outlets. You may have a coffee pot ,toaster, and microwave all on the same circuit ,no problem, unless they are all turned on at the same time. Besides the welder requires 50 Amps for maximum output and duty cycle.

    Bookmark   December 8, 2004 at 1:26AM
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I would do a convenient single outlet off a dedicated 50A breaker, then make up a cheater 20-30' extention cord to extend the physical range with the proper plug ends...by the time you run the wire around the peremeter for the 2nd outlet, you'll have double the length of wire over an extention anyway. and I think a second dedicated breaker is probably going to be required by code for that second outlet. I do know they frown on multiple wires off the breaker connection.

Could you accomplish the same end with single wires off the breaker feeding a junction box with adequate beefy screw terminals intended for that purpose.. split it in the box, then run your 2 outlets off that set-up? It would still be a single dedicated breaker (outlets used one at a time) 2 wires off a breaker is a no no, but it' may be a different animal when you stack 3 terminal spade eyes on a stud. run that by a licensed electrician for a ruling...I'm guessing here.

I suspect they'll take the "dedicated circuit" thing seriously but the "after the fact" junction box split may be OK... if it ever becomes an issue...like a fire investigation leaving a loophole for the insurance co. bulking on coverage, or a claim.

    Bookmark   December 8, 2004 at 8:52AM
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>tap the line in a splice boxscrew terminals on a UL approved terminal block vs. twisted wire and wire nuts...unless I jumped to conclusions.

    Bookmark   December 8, 2004 at 8:57AM
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I will add, that if that's a sub panel, you want to keep the earth (equipment) ground separate from the electrical (neutral) ground in that box and feed it with 4 wires, and only connect the earth ground to the electrical ground in the main service box to comply with 2002 codes. they're funny about grounds these days...and it makes sense when you think about it.

    Bookmark   December 8, 2004 at 9:11AM
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Your inspector may not like the idea of putting two 50 amp outlets on a single breaker, but according to NEC Art 210, you are allowed to do this.

Also, a question was recently posted about circuit size required for a welder. According to NEC Art. 630, you are allowed to derate your circuit ampacity for electric transformer type arc welders. For example, if your nameplate full load amp rating is 52 amps, and the duty cycle for that welder is 20 percent or less, you can use a derating multiplier of .45. That means that you can put that welder on a circuit rated for 30 amps.


    Bookmark   December 8, 2004 at 10:00AM
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Hey Goose,

Thanks for the info about circuit rating for welders. This means I can put a 50 amp buzz box on a 40 amp 220 circuit.

I am a bit puzzled, though, by the derating multiplier. I'm guessing what that means is that the 40 amp breaker won't trip if 50 amps is drawn for a brief time (2 minutes out of 10 minutes) on a 20% duty cycle, although that goes against what seems logical.

Anyway, here's another question: Is there any reason why I can't wire up a 50 amp AC buzz box with an older style 50 amp plug (triangular blade arrangement) instead of what appears to be a newer blade pattern? I ask because the outelts in my workshop have the triangular pattern (one vertical blade, with two angled blades under it) on the 50 amp outlets (served by 40 amp breaker!). I'm guessing the triangular pattern is an older style but that it should work just fine. I also notice that the buzz boxes come without the plugs (or at least the plugs are not attached) so that there is some flexibility in plug choice implied.

    Bookmark   December 11, 2004 at 4:33AM
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The older plug is 240 V with ground (3 wire), the newer is 120/240V with ground (4 wire). A welder is typically a straight 240 load (some MIG/TIG units do need 120 V) and the neutral (required to obtain the 120 V) is not needed.

    Bookmark   December 11, 2004 at 3:36PM
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Thanks Brick,

But the newer plugs I've seen included with the Lincoln buzz boxes are also three prong. The difference is that the two bottom plugs on my outlets form about a 60 degree angle to each other, whereas the plugs that come with the Lincoln have the two bottom plugs in line with each other (as I recall). Both are rated for 250 V 50A, so I suppose that's no problem.

And I'm assuming that the "top" prong is the ground, and the two canted prongs below are the two hots.

    Bookmark   December 11, 2004 at 9:11PM
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Article 630 really means that the 52 (input) amp welder with a 20% duty cycle could be wired with a 60 amp breaker (the smallest standard size larger than 50 amps) and could use #10 wire. Such a circuit could (legally) be used only for a welder of that specification. The use of a large-enough breaker is necessary for the machine to work. My big Lincoln stick welder is 100% duty cycle at 150 amps or less and 60% at 250 ampsDC. It is difficult to weld with stick much more than 6 minutes out of 10. Electrode changes, slag chipping, clamping, aligning, etc.

    Bookmark   December 19, 2004 at 8:52PM
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Bus Driver,

Yeah, that's correct on the wire and breaker size. I was reading through that section while I was trying to do something else, and didn't take enough time to explain that part. I'm glad that you posted to clear that up.

I usually install outlets at the same breaker and wire size as the outlet without derating, to make sure I don't allow for some future problem to develop, in case the outlet should be used at the full rating of the breaker. Like you said, a derated circuit could legally be used only for the welder of that specification.


    Bookmark   January 3, 2005 at 9:01PM
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Even if I hung a sign on the wall that said, "20 percent duty cycle welder only," I'm sure my inspector would red tag the installation of ten gauge wire with a 50-60 amp breaker because of just that potential "future use" goosberry suggests. I've had that discussion with them. See the OP above.

On the other hand, the AHJ doesn't want the house and the detached garage subpanels grounded together even though I'm running phone and cable TV between the buildings. Go figure.

    Bookmark   January 4, 2005 at 12:27PM
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I'm not understanding why a lower duty cycle would make it ok to use equipment rated for above the breaker rating in the first place.

After all, wouldn't the equipment, if run at full power, will be drawing more amperage than the breaker is rated to provide? Even if this is only for 2 minutes out of 10, 2 minutes is more than enough time to trip a breaker.

Perhaps a better solution would be to intall a stop in the power control on the welder so that its now reduced maximum power-draw cannot exceed the breaker rating. This would limit the thickness of metal that could be welded, but that is perhaps preferable to welding together wiring inside the walls.

    Bookmark   January 4, 2005 at 8:26PM
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The breaker is sized for the unit. The duty cycle allows the wires to be reduced in size since they will not carry the full rated current long enough to overheat based on the duty cycle of the equipment.
This is how you can have a 60 A breaker feeding #10 wire (normally limited to 30 A). It is perfectly safe and relies on the fact that the utilization equipment will provide overload protection. All the breaker is doing is providing short circuit protection.

    Bookmark   January 6, 2005 at 9:03PM
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