[Chips O'Toole]

I finally got around to putting a 250V socket in my workshop, and it will work fine for my welders. Now I want a 25-foot extension cord, because the little-bitty cords they put on welders and plasma cutters are incredibly useless and possibly sadistic.

All the prefab cords I see online are 8-gauge. My plasma cutter sucks 46 amps at top performance, according to the manual. Seems like I ought to get 6-gauge cord and put my own male and female ends on it. Wrong or right?

It seems obvious, but you would think that if 6-gauge were needed, people would be selling cords, so maybe 8 is enough.

So far, everything in the circuit is 6 or bigger.

[Radishfever]

Here is a voltage drop calculator.

I played with it and if you got 8 gauge copper at 25' and the percentage of voltage drop was .62%

According to a quick look it appears National Electric Code accepts up to a 5% voltage drop.

I have heard a few welders swear that the commercial available welding extension cables were better and cheaper than homemade versions. One thing to consider is getting really good cord receptacles with a commercially made cord.

Get multiple opinions and it would be good to hear what you decide.

Do not decide on my opinion. Worked in construction and do my own work no problem but I'm not a licensed Electrician.

https://www.powerstream.com/Wire_Size.htm

[Bill Beauregard]

Most power companies strive for 240 Volts at the street transformer.
Most of my welders are designed to operate at 230 volts.
If I lose 3 volts between the transformer, and the meter, a bit more between the meter, and the house panel, then more in the feeder to the sub panel in the house where a second feeder goes to the garage. Then a circuit for the outlet. finally an extension cord.
Each of these runs loses some voltage. Whenever cumulative loss lowers voltage below design volts, the machine's performance is affected. Voltage loss is cumulative.

Some inverter machines are designed to run on a wide range of voltages. These machines don't perform poorly if voltage loss is not great. Though amperage will rise with voltage loss, in turn causing more voltage loss.

Transformer welders get hotter internally with voltage loss. It's about magnetic choke. Electromagnets impede the flow of electricity. At design voltage, or slightly above, current is limited. As voltage falls current increases. Energy not used otherwise becomes heat.

Manufactured cords might be very well made, or they may not be.
A #8 copper cord insulated for 125 degrees C will not overheat from your welder. Consider total voltage loss. Code recommended 5% is 12 volts. I would strive for design voltage at the welder. Less than that performance will suffer.

[Chips O'Toole]

Thanks for the replies. I get 250 at the panel here, almost exactly.

[LanceR]

I suspect that the reason you are unlikely to see a 6 ga. cord is that there are darn few things that draw that much power that aren't hard wired and stationary. And unless you will be spending a significant amount of your welding time running long beads near the top of the machines capability you'll never need to worry about heating the cord up too much or starving the machine.

[cornmuse]

I got for free, (no, not stolen, legally!!) 150' in 2 pieces of 6-4 ex cord (4 = red black white green). Used 'kearny' nuts to splice, cut green short, 50A plug & outlet. Old Miller thunderbolt AC - Lincoln 180 dual mig - TA 185 tig. All worked most excellently at the end of 150'. Peace of mind would justify how much to spend, , , , ,

[Radishfever]

Um, ok but for a small mathematical difference between your situation and the original poster. You are running 150' of 6 gauge and the original poster is wondering about running 25' of extension cord. You have a grand total of 125' difference in length. I'm not going to bother plugging the numbers into a voltage drop calculator because if you are running fine off 6 gauge at 150' the original poster will be saving money, carrying less weight and will be experiencing less voltage drop at 25' of with 8 gauge.

That leaves you extra money for things like mortgage, health insurance and ride to the voting booth next November!

[Louie1961]

You are forgetting that the calculation of wire size and ampacity requirements change for a welder circuit, based on duty cycle. Unless the duty cycle is 100% at your 46 amps, you do not need 6 gauge wire. In fact, my Millermatic 252 draws 46 amps at max output and per the owners manual I only need to feed it with 8 gauge wire. And I wouldn't sweat the voltage drop, unless you are more than 130 feet from the main panel including the length of the extension cord.

[Chips O'Toole]

Louie, I think you have the right answer. I didn't think about duty cycle. My machine's duty cycle is 50%, but in actual use, it would be more like 10%, because I don't sit around cutting thick steel for 5 minutes at a time.

The cord on the machine is like an elephant's trunk. Very thick. Somewhere, when I was installing the circuit for it in my previous location, I got the idea that I had to have a 60-amp breaker and #6 wire. Maybe that was because the run to the panel was over 20 feet, and I wanted to go oversized.

I am looking at the manual, which I found online. It recommends #8 extension cord, but a 100-amp slow-blow fuse. I don't get that. They must be expecting a gigantic but very brief surge every time I turn it on. The idea of putting a fuse that big on #6 or #8 wires seems strange.

[Louie1961]

I am looking at the manual, which I found online. It recommends #8 extension cord, but a 100-amp slow-blow fuse. I don't get that.

My Syncrowave draws something like 90 amps at max output. I run it (as per the owners manual) on 6 gauge feeders and a 110 amp breaker. The NEC has a formula for how much a circuit breaker can be over rated vs the conductors, based on the duty cycle and a couple of other factors. The fact is a 6 gauge wire can easily carry 100 amps for 2 minutes out of 10, if you allow for proper cooling time.