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Wire Size Question

Steve Frazier

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I wired up my shop for a welder with the 50 amp circuit suggested in the owner's manual. I used 75 feet of 6 gauge wire that got me to a central location in the shop. Now if I use a 40 foot extension cord I can get the welder to any area of the shop. Here's the problem: every chart I look at says I should use 6 gauge wire for that extension cord but I'm seeing ready made cords advertised at a 50 amp rating that are using 8 gauge. I can buy one of these ready made cords for what just the 6 gauge wire would cost me. So which is right??
 

Delmer

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You can buy 16 gauge extension cords that have 15 amp plugs on them. Range, dryer, microwave cords are all undersized for the amps they use compared to building wire. The safety factor for building wire must just be higher than for cords?
 

mitch504

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Amperage charts are for what amperage will heat the wire to a certain temp. I'm guessing cords are rated a little higher since they aren't enclosed, but are out where they can get ventilation?
 

Birken Vogt

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National Electric Code article 630 applies to welders. Wire sizing under 630 is totally different than general wiring.

It references the name plate of the welder, duty cycle, etc. For a standard low duty welder you may use as little as 10 or 12 gauge and still be within code. But I wouldn't do it myself.

Code applies only to the permanent wiring, of course. But it gives you some idea of what you can do and still be OK.

Most 50 amp stick welders I have seen use 10 gauge wire for their factory short pigtails. That is what I have done on long extensions for ease of moving around. But if it makes you happy you can bump it up to 8 if you want to.
 

crane operator

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I guess I'd kind of like to know what the welder is, what your power source is (1 Phase-3 phase?) and what you're trying to weld.

If you're just tinkering in the shop building benches, fixing the lawnmower, putting exhaust on a car with a 110v or even 220 "buzz box" or small MIG wire machine, you can easily get by with a standard 50' 10 gauge drop cord. You wouldn't have the amps cranked all the way up, and you wouldn't be running for hours on end.

If however your running a old 220 machine stick welding, or a big 3 phase rig, hard facing a D8 dozer blade, building a bucket or rebuilding one, or something taking a lot of amps and pushing duty cycle, that's where you see issues. That's going to really heat up everything, and you're going to be pushing everything. Once the wiring gets warm you're going to see amperage loss.

A little more info would help, sorry.
 

Jumbo

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#6 would be required in conduit, or building walls (heating issues) when you have cord, you are allowed to downsize your wire size because of open air. This is a quick /rough explanation of what you are being shown or told. When you are referring to #6 and #8, you should be referring to copper, not aluminium wire.
 

GaryHoff

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One other important fact is that ac current travels mostly on the surface of the wire, thus stranded wire will have a higher current rating than solid core wire. For general purpose welding, you will likely be ok with the premade cord.
 

Steve Frazier

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Power source is single phase 220 and yes, the wire is copper. The welder is a 250 amp mig and I'll mostly be working with 1/4 inch or less, but there would be the occasional repair to my plow or skid steer and attachments that could have it at capacity. I won't be doing production work by any means. It sounds like one of the #8 cords will be sufficient.
 

Birken Vogt

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#6 would be required in conduit, or building walls (heating issues) when you have cord, you are allowed to downsize your wire size because of open air. This is a quick /rough explanation of what you are being shown or told. When you are referring to #6 and #8, you should be referring to copper, not aluminium wire.

I don't think so, I can't see where any larger than #10 would be *required* under article 630, can you show me if I am missing something? I agree all assumptions are for copper wire.

One other important fact is that ac current travels mostly on the surface of the wire, thus stranded wire will have a higher current rating than solid core wire. For general purpose welding, you will likely be ok with the premade cord.

Skin effect is not appreciable at 60 Hz with wires this small.
 

Jumbo

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I don't think so, I can't see where any larger than #10 would be *required* under article 630, can you show me if I am missing something? I agree all assumptions are for copper wire.

Skin effect is not appreciable at 60 Hz with wires this small.

To the receptacle, #6 is required since multiple loads could/might be plugged into the receptacle. When you are dragging 40' of cord, #8 is needed for the length. The #10 pigtail on the welder is a short either 4 or 6 feet depending on the year of the welder and the code cycle. The welder is considered an appliance and manufacturers get away with having the appliance pigtail be undersized and kept short to save money. If you are running the welder full bore and over the duty cycle, (we all do) you can both burn up the cord and/or damage the welder. Electrical service calls to fab shops are all about undersized and over length cords.

You are correct regarding the skin effect on small conductors, of course, building wire is manufactured stranded #8 and larger only. Solid #6 can be found only in bare for grounding electrode installation. At work, we quit pulling solid wire for anything in the mid 70s due to excessive labor for pulling and terminating solid wire.


The only other suggestion I might offer, is to review the jacketing on the cord you buy. some of the premade cords are made for generators with lightweight jackets. Look for an SJOW cord jacket (I included the letter designations fyi.) An SJOW can be driven over with no lasting damage, it can have heavy objects dropped on it and other forms of abuse not planned for but usually happening in a shop.

I also included the designation "P", zip cord is what is used for your welder pigtail.

S = Service Grade (also means extra hard service when not followed by J, V, or P)
J = Hard Service
P = Parallel cord (also known as zip cord)—Always light duty
O = Oil Resistant*
W = Outdoor—includes sunlight resistant jacket and wet location rated conductors (formerly "W-A")
 
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