120V MIG welder and extension cord

I was looking at a Lincoln Weldpak 140 which uses 120V input power. I have a small shop at the back of my property and I would like to use the welder out there. What kind of extension cord do I need?


You would need to know max amp draw and the distance to your shop.

The distance is about 100 feet. By max amp draw, do you mean the input amperage? If so, that is 20A.


You should probably go with a #8 wire size.

Could you run a line out there? Use 12/2 underground. $79

You only need a narrow trench. Go down about 12 inches.

#8 would be pretty safe. Try this calculator.

You may find the cable costs more than the welder.

I recommended 12/2 ground because thats what most home circuits use. It’s rated up to 20 Amps. Most circuits in a home have a 15 Amp breaker which can use 14/2. But electricians over size the wire with 12/2. That’s all a standard house receptacle can handle.

wire size chart

These welders are meant for home shops. Even so, are they likely to pop my breakers?


You’ll need a 20 Amp breaker on that circuit. The electrician will need to confirm the old circuit has 12/2 wire before replacing the 15Amp breaker with a 20Amp.

Its illegal to use a 20amp breaker with 14/2 wire.

Really you need a dedicated circuit out to your shop. Thats what I did. I buried a wire and ran it up to my panel. My electrician wired it into the panel with a 20 amp breaker.

I have a double receptacle in my small shop and one ceiling light.

Ace, I think the big challenge is the 100 ft run. Even if he gives the shop a dedicated 20 amp circuit he will still need 8 guage wire, 10 would likley work fine but with electricity best to go bigger than smaller.

I’ll defer to more experienced voices. a 100ft is a long run. I wouldn’t even consider an extension cord. If it stars raining… you got problems.

Agreed. And if you go direct burial go deeper than 12 inches.

I probably went a little deeper than 12 inches. I used a standardtrenching shoveland sunk the blade below the ground surface. That gave me a good guide to dig evenly the entire length of my run. For a 120v line powering a couple of shop receptacles that seemed plenty deep.

Consumer grade 120v welders are designed to plug into a standard wall circuit and work. A dedicated line is preferable but there’s a lot of homeowners who use their standard garage outlet. That’s why I gave advice for running a standard 20amp 120v line. But, it is a good point that 100 ft run changes things.

If a 8 or 10 gauge is used that will require a subpanel on the other end. A 8 gauge wire won’t fit onto a standard 15 or 20 amp duplex receptacle. The electrician will probably run a feeder line out to the shop and wire a subpanel with breaker out there.

If you don’t mind HUGE, DANGEROUS KLUDGES:
A 20 Amp outlet has a T shaped connector.
Check you breaker box - is there a 20 amp breaker in there?

If there is only 1, it is likely (newer homes, USA) a dedicated line for the refrigerator.

You can get a 100’ roll of 10/2, a 20 amp plug and socket and plastic conduit.

When you want to use welder, unplug refer and plug in Frankenstein cord, run through a window.

This violates only 3 or 4 of the sections of electrical code, but would get power without the time and expense of running a new circuit.
If you do run a new circuit, make it at least 30 amps, which is going to very expensive wire, but you won’t need to worry about being on the ragged edge of tripping the breaker.

If you’re going to be running new circuits to the shop, look at the Weld Pak 180 - this model runs on 240.

The Weld Pak 140 runs right at the hot, ragged edge of what a 120-volt circuit can deliver, but a 240-volt circuit will barely be breathing hard if you go with the 180.

Well, I already have a Lincoln AC/DC 225/125 welder. If I get a 220 circuit, I will just plug into that. After getting sticker shock looking at extension cord prices, I think I will just plug the thing directly into the exterior outlet on the house. If I am not running it full tilt, will it run at the ragged edge?

I looked at my breaker box last night and saw that have the breakers were 20A and half were 15A. However, most of the 15A breakers were just labeled “Lights” and so I am not sure what goes to the outlet outside without flipping them all one at a time and seeing what gets turned off. There is one circuit on a 20A breaker marked “Kitchen GFI”, (the kitchen is near the back door where the exterior outlet is), so maybe I will start with that.


Let’s assume

Branch voltage = 120 VAC
L = 100 feet
Max T = 100 °F
Conductor material: copper

Then the voltage drop at 20 amps would be

6.2% if using 12 AWG wiring
3.9% if using 10 AWG wiring
2.5% if using 8 AWG wiring

A rule of thumb I’ve heard is that the voltage drop in a branch circuit should not exceed 3%. So based on the above, you would want to use 8 AWG wiring. (And for your application, the actual voltage drop is bit higher than 2.5% for a variety of reasons.)

If you go the extension cord route, you will probably have to buy 100 feet of 8/2 outdoor-rated cabling - which will not be cheap – and then connect a 120 V/20 A plug to one end and a 120 V/20 A receptacle to the other end.

My advice? Stop pinching pennies and do it the right way. Put a 100 amp breaker in your main panel, a 100 amp sub panel in your shop, and run aluminum URD between the two. You can then install 120 VAC and 240 VAC receptacles in your shop.

A head’s up - if the exterior outlet is near the kitchen and the kitchen has a GFI, the outlet is probably wired downstream from the GFI - that gives the exterior outlet GFI protection without the expense of adding another GFI.
It also means than anything plugged into the GFI will subtract from available amps at the exterior outlet. If you’re running the welder at 20A and somebody decides to make toast using the GFI in the kitchen, you are now drawing over 20A.

Plugging a welder into a kitchen GFI circuit is almost guaranteed to end in tears, heartbreak and swearing. MIG and TIG welders are notorious for tripping and occasionally destroying GFIs.