220V Extension Cord for Welding

erikmannie

erikmannie

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I ran out of space in my garage, & now I am moving my welding table outside.

My 220V, 40A outlet needs to stay where it is because it is needed for 3-phase machine tools.

At this welding outlet (I will post a photo), I have an extra 4-prong, single phase female receptacle which is no longer needed.

I want to dedicate that second outlet (which also has a 40A circuit breaker) for my welding. My welding will occur about 50 feet away from here. My welding machines are all single phase 220V & only go up to 255A.
 
I will TIG inside the garage (distance from outlet is 20 feet), and MIG + stick outside at a distance of 50 feet.

My Dad is a retired electrician, but he has some health challenges which affect his manual dexterity. He will direct me to do the work. We don’t need to work at the panel because I have been using the 40A circuit breaker for years, & it has never tripped.
 
My questions are:

(1) Should I run wire (in a conduit) from the outlet along the garage wall in order to hard wire a welding outlet closer to the welding site? I don’t see what I would gain from this. The wire coming from the panel is either 8 or 10 AWG, and the extension cords that I am looking at are 8 AWG. A conduit along the wall would be ugly, & would move the outlet farther away from the TIG welding area.

(2) Am I okay with a 50 foot, 8 AWG extension cord for my 220V welding up to 255A?
 
As I understand it, the penalty for using an extension cord (or a longer electrode lead, as in stick welding) is the need to turn up the Amps on the machine every time you weld using an extension cord. This will nerf my machines a little; where I could have run a single bead on 1/4”, for example, I may now need to add another pass for that.

I understand that I will pay a little more money for kWh that were lost to heat, but I am prepared to accept this.
 
One wonders what percentage of extra Amps are required for every 25’ of lead.

My machines came with a 6’ cord. I could have tried to make do with a 25’ extension cord, but that would have been too short for some jobs.

With a 50’ extension cord, I can do everything that I want to do.

Hopefully I will be okay to move forward welding up to 255A with an 8 AWG, 50’ extension cord on a 220V, 40A circuit.
 
8 AWG copper has a resistance of .064 ohms/100ft. Power lost will be I*I*R, so worst case is 40 amps * 40 amps * .064 = 102 watts per 100ft. Call it 1 watt per foot. Additional voltage drop for the extension cord will be about 40A * .064 ohms = 2.56 volts. You'll get some extra loss due to the additional plug but not much. Overall I doubt you'll notice the difference.

editted to add: That said, I'd probably look for 6 awg cord since you're probably using a 50A plug. That way your cord is safer for use on any 40A or 50A circuit.
 
Last edited:
rabler said:
8 AWG copper has a resistance of .064 ohms/100ft. Power lost will be I*I*R, so worst case is 40 amps * 40 amps * .064 = 102 watts per 100ft. Call it 1 watt per foot. Voltage drop will be about 40A * .064 ohms = 2.56 volts. You'll get some extra loss due to the additional plug but not much. Overall I doubt you'll notice the difference.
Click to expand...
So 2.56V per foot, or 128V over 50 feet.

128V sounds like a lot!

I guess the welder adjusts for this by turning up the machine a bit.
 
Here is the outlet that I am working on today. I am going to change the 4-prong female to a 6-50R (3-prong) female.

image.jpg
 
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