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240v wiring Size

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12K views 42 replies 8 participants last post by  Sberry  
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#1 ·
I need to run a 12 foot 240v line for my welder. My welder calls for 50 amp breaker, I need to know what size wire to get and what kind of wire that I need.

My current line is very short and my welders amp and voltage gauge keep droping from what I set it to. Ex. if I set it to 125 amps then Ive seen the amperage drop to 60 and 30 amps while welding.
 
#2 ·
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#3 ·
We use two formulas to size conductors. Then we choose wire size.
Ampacity is defined as the level of current expressed in Amperes a conductor can carry without overheating. Insulation is rated for temperature tolerance. Ampacity of 90 degree conductor is higher than 60 degree. In many cases ampacity is restricted to temperature rating of terminations. Used to be many terminations were rated at 60 degrees F. Now, 75 degrees is more common. In the application of a welder conductor heat is limited by welder limited duty cycle. Code has an article dedicated to welders. Based on your duty cycle, you may be allowed to use smaller conductors.

The other formula you need to consider addresses voltage loss. Voltage loss is a complex formula as it factors each conductor between your transformer at the street, and your welder.

Without running the formulas I say cost difference between #8 & # 6 will not be great. Then you can plug a different welder without concern. You can even upgrade the breaker easily if a bigger welder is in your future.

You say amperage drops off while welding. I once had a welder with VERY low duty cycle. It didn't shut down when it reached duty cycle it tapered off on amperage.
 
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#4 ·
Willie is not wrong, but honestly most manufacturers do the math for you and specify a minimum wire size in the owners manual. I would check your owners manual first. Here is an example from the owner's manual for my MM255. NOTE: normal assumptions around how many amps for what gauge wire do not apply. The electrical code allows for different specifications for a circuit dedicated to a welder. You can see this in the picture below. For my welder, the mfg recommends a 90 amp breaker with 8 gauge conductors.

View attachment Screenshot 2023-06-20 111046.jpg
 
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#6 · (Edited)
I am running two different machines, one is a transformer style stick welder. The other is a inverter style multiprocess machine.

I am using the stick and tig welding process currently, I have tried flux core but am have the same problem on the CV side.

When I start to weld on CC my amps are dropping from my set amperage at 125 amps to 60 and 30 and it fluctuates. The transformer machine will hold a better arc than my inverter will.

I'm running a new line from my electrical panel and replacing the receptical outlet and changing my breaker. Need to know what size and kind of wire to get.
 
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#8 ·
Louie, should be noted that if that machine is wired that way it is for that machine and not a general outlet for other welders. They allow that for an outlet to a dedicated machine. There are a lot to the exceptions above 50 and even 60A. While it lists 8 that is not for a cable but single circuit in pipe and not with 10 ground but it is to be sized up to number 8.
I hate to use a blanket statement that if a guy upsizes some of the wires he can simply use the circuit for all types of machines. May be fine for someone as experienced as Willie to do as he sees fit but the lay people need to follow some basics such as unless its a specialty a 50A breaker on a 50 outlet. The breaker is not really intended to protect this circuit from thermal as much as it is for short circuit and these smaller machines need to be on a current limited circuit.
The straight small 240 machines for sure and maybe the new mvp might not matter???????????????????????? Maybe the adapter is rated for higher fault protection than 50A? I dont know as I would wire it that way without engineer,, it lists max breaker as 50. Is designed to be allowed on a 50 circuit.
 
#14 ·
Sberry said:
Louie, should be noted that if that machine is wired that way it is for that machine and not a general outlet for other welders.
Click to expand...
Granted, but if one machine requires 6 gauge conductors and a 100 amp breaker and the other machine requires 8 gauge conductors and a 50 amp breaker, I would personally install 6 gauge and the 100 amp breaker and use it for either machine (one at a time, not both at once). In fact this is what I did when I owned both a Syncrowave 250 and a Millermatic 252. Now we could get into an argument over whether using a 6/50 plug and receptacle are allowable on the Syncrowave setup (100 amp breaker with 6 gauge conductors), but that's what I did and never had a problem. In fact, when I sold the syncrowave and the MM252, I kept the same wiring and just downgraded the breaker to match the MM255's needs

I am running two different machines, one is a transformer style stick welder. The other is a inverter style multiprocess machine....I'm running a new line from my electrical panel and replacing the receptacle outlet and changing my breaker. Need to know what size and kind of wire to get.
Click to expand...
To the OP...do what I outlined above.
 
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#9 · (Edited)
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#11 ·
As for using this circuit for bigger future welders those are sposed to be dedicated circuits, single circuits in pipe with upsized ground wires that match the current rating of the breaker. Not the 10 wire in a cable. Worth noting the same wire may be listed on couple older 50A machines and on dedicated circuit up to 100, the thermal must not be all that sensitive of an issue if it has such a range but,,,,,,,,,,,,,,,,,,,,,,,,,,,,, very specific change to the ground wire,,, musta been important????
 
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#13 ·
Ground conductor only should carry fault current. A fault to equipment ground is likely to instantaneously be limited in current only by the limits of the power supply (typically 10,000 Amps). The breaker should open near instantly. Heat in the equipment ground conductor is rarely a concern. For the same reason we need a smaller conductor for a low duty cycle welder, it takes time to heat a conductor, we can use a reduced equipment ground conductor. Article 250 NEC gives the specifics.

There are exceptions:
Last week we were replacing an old Federal Pacific Electric service panel. The basement sill had been heavily foamed over & I couldn't see if there were cables there. I probed with a screwdriver & found none. I drilled out through wood & vinyl siding with a 1/4" pilot bit to locate outside. Suddenly, the sky opened up, a real downpour!
Next day, first step, Seth bored in with a hole saw. There was an arcing noise & smoke, lots of smoke! Paniced, I punched the code for the key box, got the key, unlocked, hurried down with fire extinguisher. No visible fire behind the foam.
It continued to buzz, the breaker didn't trip. I turned it off manually
 
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S
#16 ·
There is an exception for the plug for dedicated machine. There is a limit to it. Its for a particular machine and not welding machines which means used by more than the one it was intended for. You will get no argument from me that it wont work just fine. I got one, out of the way, dedicated to 300, I never use it, the other machines have a home and general available, all at 50A, I believe my feeder could be wired 60, its not an issue. Biggest cord I own is 10, longest common circuit could get a 120V welder is 50 ft, meter,,, not a chart but meter says less than 4V drop wide open at 22A.
 
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#17 ·
Seems every welding circuit uses the breaker size to determine the load? Some guy comes to a forum and says I add all the breakers up in my panel, I would be overloaded, he gets an explanation that it dont work that way,,, but Bill comes here and asks about a welder rect 12 ft away and he has to start calculating V drop from his tranny with a 200A load on it????? From some of this it would seem impossible my Bud run a welding shop for 40 years from a used 100A panel, air comp, couple welding machines, a lathe and a few lights. Weld trailers out 2 machines at a time. I have seen several 300 run from 100 service just dandy,, a guy really has to burn to get to 60A,,, super hard at 70
 
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#18 ·
He said his welder drops amperage. I have an industrial facility where they get the same issue in the welding shop. Their feeder is 200 feet long #6. They have resisted my advice to buy an inverter welder & did buy a Miller Bobcat 250 engine welder to resolve the problem. I think there are a good many shops with very significant loss due to long runs & small conductors.
 
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#19 ·
What you might do, a guy like Louie who can work upsupervised is a bit different than a diy guy first timer. You are on the top of the heap and on auto pilot and ready for anything comes along. I am an inverter advocate and not really due to someone thinks they got to max it all to the end but for the guy now can wire for 30A service machines with 12 cords if they want, they can buy an 8 for that matter but 12 is legal with those ends, 50 ft or 2, either voltage and making convenience outlets and branch circuits affordable for these machines instead of cords or allows for utilization as they say is great.
I got no problem with a guy spending up some, certainly have used a lot of chunks of old cable and cords over the years for welding with machines that were rather greedy and we often abused. My neighbor put in a recep 40 yrs ago with a 10/2 w/g, the ultimate wireman, got it still on 2 fuses. Never needed a larger machine, neighbor the other way was a diy in this respect and put in 10/30 and never need a bigger one in 22 yrs. He can/could, just didnt need it.
 
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#22 ·
I take care of the local school. For 120 years the boss of the lunch ladies was wife of my grandfather's extra son. Father never knew why, my grandfather loved this guy. He married, & after my grandfather died, he had a severe drinking problem. My father became his surrogate father, beat the alcohol out of him. He lived 30 years dry. For reasons I never figured out, his wife HATED me.
She was forever having fund raisers at the school where she would plug two power strips end to end into one receptacle. Every borrowed microwave, toaster oven, or crock pot in town was plugged in. It always tripped the breaker, proving I "didn't know what I was doing". By this time, her son Randy had graduated from electrical school. "I asked Randy, he said I should be able to plug in anything I wanted to!" I doubt Randy understood she was plugging 5 microwaves & 5 crock pots into a 15 amp receptacle.
She went to the school board, said I "do not know what he's doing!" I had provided 160 amps of receptacles to the serving counter, she insisted on plugging into one outlet.

When I confronted her, she said "I only want it for one day!"
 
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#24 ·
Nah, they've been a member since 2017. They'll prolly be back soon.

Also -

15 feet of 6AWG copper, 50A, 240V, single phase AC load should be a 0.61V drop. 8AWG would be 0.97V.

I have a voltage drop calculator on my phone...

Sent from my Lincoln Buzzbox using Tapatalk
 
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#41 ·
You are a guy along with a couple others here are sharp enough and got the talent some study with this would be very worthwhile. I got a neighbor the same thing, his mechanical is fabulous but no one ever caught it and go over a couple real fundamentals that they are missing. I try that on occasion here but it gets clouded and some of the guys that should be the most help add to the conclusion,,,, then,,, we get a guy does it right, goes to some effort to learn then we get that guy,,, but I would do it this way if it was mine and cause a loss of well earned confidence from a genius doesnt know shat and aint gonna learn either.
Very good reasons for more senior guys to learn,,, 1,,, can go back and fix some faults they7 may have created along the way, my bucket list is shorter with that and secondly,,, if you know correct then the others, sons grandsons etc will know also instead of another generation of guys learn hand to mouth,,, someone told me, I was always told are the w2orst consultants in world history. Its well worth a code book,,, even old one 2002 or so is fine and find a forum to follow along and thumb thru the book.
There are some smart azzes on forums and a lot of young genius and can almost tell when they are studying for masters or have just finished it. Despite some attitude they are great to follow as they are current with the language and interpretations.
 
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#42 ·
Some of the confusion will disappear with some understanding, the code is not a great diy, its good for some guys with some experience. Once the learning starts the idea that some have that they can outhink it will go,, the way of doing "as I understand it" will be replaced by "following the instructions".
Someone commented the other day, I took a couple minutes and read the instruction sheet come with it. Lots of information in the simple service guide to a we3lder, it almost needs to be understood word for word and meant for someone already has a clue and makes little sense to a handyman type, It involves soooo many principles of rating and protection in one simple circuit that is rather invisible at first glance. Not that it cant be improved but should be understood that its safe and adequate provided the instructions are followed.
There is a great mis understanding about codes, in some cases they are minimums and more used as a design guide, must be 120% of this, 80 that, doesnt mean 310 is the bare min but that it is adequate and to be used as directed,,, and they raise the voltage 10% wayyyy after that chart was adopted, welder used 42 now uses 38A. Higher voltage has improved utilization, every cord carrys the same watts with less current load, less lag and sag on every breaker and circuit with the same piece of equipment. (worrth noting some models use same wire at 208, some they allow less at 240.
My DC buzzer is 92 on an 85 setting and 118 on 105 and the numbers would be closer at its 230 rating, the problem is or isnt that its suffering from V drop,,,, its over on a modern service.
 
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#43 ·
I have to go to work but,,, so much equipment now trips breakers at starts, so close to hot service a chop saw, some small air comps, those motors with close prox to service and huge wires dam near tear out like dragster on starts. My helper at the time, mean well but cant do a fukkin thing like you tell him managed to run to my saw recept where I wanted 12 for some choke. Need a 30 on it or add 25 ft of 16 cord to it to keep it from trips.
 
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