Welder Extension Cord Size

[FThera]

I have an Esab Migmaster 250 that I use for home hobby work and would like to add an extension cord to. It's rated input is 62 amps @ 230 volts, and 250 amps output @ 50% duty cycle, and I'm looking to get a 50' extension cord.

I ran several different wire sizes through a couple of different online voltage drop caculators and got the following results. My voltage at my wall plug is 240 volts.

6 awg = .9% voltage drop = 2.16 volts = 237.84 volts.

8 awg = 1.5% voltage drop = 3.60 volts = 236.40 volts.

10 awg = 2.3% voltage drop = 5.52 volts = 234.48 volts.

12 awg = 3.8% voltage drop = 9.12 volts = 230.88 volts.

I appears that all the above wire sizes will provide voltage to the welder that are in excess of its rated input voltage (230 volts), even the 12 awg while marginal (I would not go that light) would work.

Am I missing something here?

 

[Aceman]

Minimum size would be 6-3 SO cord.

With a 62 amp input at 50% duty cycle we're allowed to adjust the required wire ampacity down to 44 amps.

#8 SO cord is good for 40 amps.
#6 SO cord is good for 55 amps.

 

[FThera]

I know that. I'm not talking about what the code says. I'm talking about what the voltage loss calcs say. Real world tells me #10 would be plenty heavy for 50% duty cycle at my rated input to end up with 230 volts PLUS at the welder. Even # 12 would do it, but it would be close.

Hell, the manual for my welder say a 50 amp circuit with #8 (thhn) wire is fine for the service wiring.

Most every welder built today is rated at 230 volts input (not 240), which leaves a lot of margin for voltage drop in the wire length on a 240 volt service. Plus SOOW wire is rated at a much lower temp than service wire. In my world of hobby welding I will NEVER get even close to a duty cycle of 25%.

 

[hidollartoys]

This is NOT about voltage drop but about current. Voltage drop is ONLY a FPN in the code and except for VERY long runs has little to do with wire gauge selection.

Choosing the wrong (lighter) gauge size is not the cheap way out if you have to upsize/replace later. Since this is an extension cord for welding and is exposed to all sorts of potential damage, I would choose the biggest, toughest wire for the job. If you are not inclined to accept Aceman's suggestion then follow the welder's manual. Not sure what answer you are looking for.

 

[nehog]

I have an Esab Migmaster 250 that I use for home hobby work and would like to add an extension cord to. It's rated input is 62 amps @ 230 volts, and 250 amps output @ 50% duty cycle, and I'm looking to get a 50' extension cord.

I ran several different wire sizes through a couple of different online voltage drop caculators and got the following results. My voltage at my wall plug is 240 volts.

6 awg = .9% voltage drop = 2.16 volts = 237.84 volts.

8 awg = 1.5% voltage drop = 3.60 volts = 236.40 volts.

10 awg = 2.3% voltage drop = 5.52 volts = 234.48 volts.

12 awg = 3.8% voltage drop = 9.12 volts = 230.88 volts.

I appears that all the above wire sizes will provide voltage to the welder that are in excess of its rated input voltage (230 volts), even the 12 awg while marginal (I would not go that light) would work.

Am I missing something here?

A bit of Ohm's law and a few other things, shows that (as an example) the 12 AWG dropping 9.12 volts would cause the wire (and connectors) to dissipate about 565 watts of power. That would result in some rather warm wire! Even the 6 AWG would dissipate 133 watts, which would be noticeably warm, but might work OK.

One does need to realize that the 62 AMPs drawn by the welder won't be 100% full time, so you would get cooling effect when not actually welding...

 

[Aceman]

It's clear FTHera likes asking questions he thinks he already knows the answer too.

Next time I won't waste my time.....

 

[Ford12508]

The reason the code is there is for safety. As soon as I opened this, I thought 6AWG before I got half way through the OP. When you are working on something and the wire burns, don't blame us.

 

[sberry]

In a home hobby shop, one wire, one gas, likely 035 wire a 10 will run that machine. But,,, the machine doers have the potential to overload that wire. Personally it would be a ready made 8 cord for me if I had to buy one.

 

[sberry]

Even # 12 would do it, but it would be close.

No, it would not, the machine has the potential to overheat the wire, also depending on breaker it may not be legal to connect a 12 to it. The potential is different between the models, a buzz box may be rated different.

 

[jinotown]

The first question would be what is your 240 volt wall outlet and breaker rated at? You don't want to make an extension rated for 62 amps if you are using a 30 amp outlet. What material do weld? If all of your welding is 1/4" or less and you never use more than 1/2 the welding power, then a lighter extension should be fine. That being said, at least match your existing outlet rating.

 

[sberry]

Good point. I lost my train of thought in previous posts. The original poster did a good job in asking and defining his needs as well as listing the machine and even expressed what he thought he knew. As was pointed out and really there are a lot of numbers thrown into a blender. As was mentioned the rest of the infrastructure wasn't listed but If I was starting from scratch in this scenario, really low demand situation I would install 50A circuit, 50A breaker, depending on length and if I had the wire, etc, cost, etc an 8 or better wire and an 8 ready made cord. You can plug anything in to it that comes with a factory 50A including SMALLER units and it will support the Esab which is going to pull about 40A. Put in a common welder circuit with 6-50-R and plug.
This machine will do beyond and then some that the owner will ever use it for, I think its high end numbers are beyond Miller 252 or Linc 255, they list 50A service. Likely running C25 gas and 035 wire cant even turn it up high enough to trip a 50. Melt the end of the factory gun off, ha.
I reach out the other day with a 250 class machine, add 25 ft of 10, weld as hard as I could for 10 minutes, walk over and grab the cord, couldn't even tell or wouldn't notice, don't care about a few watts loss for few minutes once in a blue moon.

 

[sberry]

The man is right to some extent about getting the thinking convoluted in the real world, here we often see,,, get a 6 so its useful for a bigger machine, well,,, the guy already has a racing unit, more likely to end up with another 180 class or stick unit, having a practical cord for those too is useful vs having a monster 6 to drag everywhere 2 sizes bigger than is needed, than he would ever notice. I got all the cords,, use a 10 about 20 times for every time I use a 6.

 

[FThera]

Just for the record I did not plan to buy anything less than a #8 SOOW for my welder. I was really commenting on how surprised I was that the voltage drop on even a #12 cord was still above the voltage that the welder is rated at (and I was ONLY talking voltage drop). I do run this welder on a 50 amp breaker because thats what the code allows as far as derating based on 50% duty cycle. I can probably count on one hand the number of times ANY of my welders have been run at MAX, usually more like 50%, and like has been pointed out above at that type of output the demand on a cord is WAY lower. If it were a production shop then a whole different story, but in my home shop and at the power and duty cycles it will see....really.....kind of like buying a 10,000 watt generator to run a toaster.