If it is a new welder, the included instructions will specify the minimum wire gauge. If not new and no manufacturers instructions, what is the duty cycle of the welder?

This is for a relative in another state, which is why I don't know distance for sure. The welder has not yet been purchased; and won't be when I get there to install. The one presently being looked at specifies 30% duty cycle @ 135 amps. It also says it operates on standard 210-240V / 22A circuit. The other one that is being considered said 30% duty cycle @ 130Amps; and specifies 20 A input current at rated output current. Seemingly they are very close in their power requirements. Neither specifies type of plug.
Appreciate whatever you can offer / suggest . . ..

Welders in attached residential garages present significant fire hazards- and that is a real understatement. For larger welders that might be purchased in the future, install a 50 amp circuit. But for one of these welders, and anticipating no present or future other use for the circuit, for a minimum installation, install 12-2 with ground, circuit breaker up to 30 amps. Those who disagree should read Article 630 of the NEC. Install the receptacle to match the provided male plug on the welder

Arc welders have their own articles in the NEC.

The breaker is only for short circuit protection of the feeder, NOT overload protection.

Arc welders provide their own overload protection.

The wire size is not as directly connected to eh circuit breaker rating as with general use receptacles.

I'm with Petey on this one, he makes a LOT of sense. There's no way to predict what the current or future owner of the property may decide to do with that circuit.

How does this work in a commercial/industrial setting? Does the circuit need to be labeled? I can imagine opening a small welding shop and installing a circuit per Article 630. Because my business is wildly successfully I quickly outgrow the space and move on. What happens to the next guy who has a kiln, table saw, etc. and sees a convenient receptacle?

Evidently the many qualifiers I included were overlooked by rushes of adrenalin from those anxious to insult. The person asked a specific question, that specific question was answered. Others had prior opportunity for over 12 hours to answer in their own way. I did post the possibility of installing a 50 amp circuit. I meant a 50 AMP CIRCUIT, no other way to interpret it. I know of no way to wire anything to preclude the wrong use of it in the future. And I would never put a welder in a residence. I have too many observations as a volunteer fireman.

I'm not familiar w 630 . . . but get the drift of what it says, and the possible danger(s) in the future by a different owner / user. Think I'll do 10 Ga, explain to my nephew the possible concerns, and label the outlet clearly for welder use. That should at least "spark" someone to look further into it if ever to be used by someone else for another type use.

Thanks to you all for you thought / ideas / suggestions / concerns . . . .

Bob

Just found some more info on welder . . . specifies that it comes with 6-50P and should be connected to a 50 amp rated circuit. Sounds like they suggest against the "lower" / special ratings of 630. So what's the ga required for 50 amp circuit @ ~ 60 feet ? At what distance would it warrant bumping up the gauge ?

Thanks again to all . ..

Bob

I'm not an expert and I'm going from memory here (actually if you search this forum, you'll find additional discussion on the subject) but the gist of Article 630 is that it allows you to undersize the wires serving the circuit of a welder. The reasoning is that welders have duty cycles and generally can't be used continuously. If I recall correctly, the calculation is a function of the duty cycle of the welder. Which poses the question, what happens if you buy a new welder with a different duty cycle.

As suggested, run full-size conductors. What gauge you need depends on what kind of wire or cable you plan on using.

Bus, don't be so sensitive. I was not insulting you. I was making a point I feel very strongly about.
There was no adrenaline involved nor was I anxious about anything. My main point was that your statement quoted in my last post makes it look like you are saying anyone who does not agree with you does not know what they are talking about. I was merely explaining how and why I disagree, not that you were technically wrong.

Of the "many qualifiers" you refer to, I see "and anticipating no present or future other use for the circuit," as pretty much the only one. HOW in the world can you predict or ensure this???

That was directed at rcmjr, the installer. So how do/did you ensure that your installations would not be abused/misused in the future?

"There's no way to predict what the current or future owner of the property may decide to do with that circuit. "

You cannot protect fools from their own errors.

The article is there and has no restrictions on commercial or residential use.

I have numerous large 240 V power tools, and even a couple of 3-phase tools.
They are all wired to the correct code articles.

If a subsequent fool tries to use them for an inappropriate use that is NOT my problem.

OK Bus. Sorry then.

"The article is there and has no restrictions on commercial or residential use.

IMO there SHOULD be!

If a subsequent fool tries to use them for an inappropriate use that is NOT my problem. "

All well and good. But what if the fool has NO idea that the circuit is wired for a welder according to Art.630 of the NEC??? Then what you have is an unsafe installation, simply by changing occupants.

I can see if the receptacle is labeled for welder use only (although not required) and someone uses it for something like a kiln. That is their foolish problem.

"All well and good. But what if the fool has NO idea that the circuit is wired for a welder according to Art.630 of the NEC??? Then what you have is an unsafe installation, simply by changing occupants. "

If another person wants to install and use heavy equipment it is incumbent on THEM o make sure the installation is correct.

Special use circuits should be identified i the panel with their purpose as part of routine labeling, but restricting the use of dedicated circuits is not going to be very productive.
They are allowed and should be used when needed.

Every hermetic compressor for HVAC gets special permission also.
The motor is cooled by the returning gas and contains overload protection.

What if the next owner wants a larger condenser?

"If another person wants to install and use heavy equipment it is incumbent on THEM o make sure the installation is correct"

Do you honestly thing someone who needs a 50A circuit in a garage for a kiln (for instance) is going to open a box, or check the wire size, to make sure it is not on old welder circuit legally wired to Art.630 yet not sufficient for most any other use of a circuit that size???
I am all for not idiot proofing things, but your suggestion that someone would or should know something like this is absurd IMO. All they will see is a 50A receptacle on the wall and a 50A breaker in the panel. And IMO it would be a fair assumption that the circuit was properly wired, and NOT just for a welder.

Special use circuits should be identified i the panel with their purpose as part of routine labeling, but restricting the use of dedicated circuits is not going to be very productive.

I don't get what you are saying. The ONLY way to assure safe and compliant use of such a circuit would be to restrict it to a welder. A label would help, but it is not required and not permanent.

What if the next owner wants a larger condenser?
Apples and oranges. They cannot simply plug in an A/C condenser.
99.999% of the time something like this would be professionally installed, assuring a proper installation.

Do you honestly thing someone who needs a 50A circuit in a garage for a kiln (for instance) is going to open a box, or check the wire size, to make sure it is not on old welder circuit legally wired to Art.630 yet not sufficient for most any other use of a circuit that size??? "

Why are you so convinced this is YOUR problem?

It is THERE problem.

I have no compunction about wiring what I need to the code.
It is NOT incumbent on me to guard latter fools who do not know what they are doing.

Any responsibility ends when you do the work to code as the present owner requests.

I have installed kiln circuits a number of times, and between the kiln manufacturers and the potters using them there is a great sensitivity to what it takes to run a kiln in a residence.

They tend to be far more paranoid than ANY code requires.
They are sleeping upstairs with a kiln in the basement at many thousand of degrees F that requires a 24-48 hours at temperature for the material, and in many cases multiples of that for cooling off before you dare open the kiln (the quick cooling would cause all the pottery to instantly shatter, so no peeking).

Three-five-seven day kiln cycles are not at all uncommon.

I don't consider it my problem. I don't consider it a problem at all. I consider it good wiring practice.

Some things I do according to code minimums, many I do not. This is one I do not.

"I don't consider it my problem. I don't consider it a problem at all. I consider it good wiring practice.

Some things I do according to code minimums, many I do not. This is one I do not. "

Correctly wired special use circuits are pretty far from mimimum.

Do you oversize the branch circuits for HVAC work in case somone later needs a bigger unit?

You could make thins even safer by using #10 for ALL 20 amp circuits, and #12 for 15 amp circuits.

I have actually never met anyone stupid enough top just plag a kiln, large compressor, welder, or other large equipment into any handy spot.

The equipment contains all sorts of warnings and installation instructions.

My 3 hp table saw requires a 45 amp breaker for reliable repeated starts.
There is no reason to use wire larger than #10 since the motor cannot overload the circuit and the starting surge is what is driving the breaker larger (NOT the running load).

Again, the A/C comparison does not hold water for obvious reasons.

Plug something like a kiln into a "handy spot"??? Come on, it's not like there are 30 or 50A receptacles all over the place.

Sorry brick, I like you a lot, but I can tell we are not going to see eye-to-eye on this one.

I would match the wire size to the breaker that is being installed so some day down the road regardless of who lives there or what they do at a minimum. If code stated you could wear pants that were 36 and a belt that was a 40 would you do it and if so what would happen?

I have 30 A receptacles in my garage. There have to be at least 2. Do I have to check out the cable before I plug in a kiln? Seriously, my wife wants a kiln!

I rest my case.

As a follow-up; here's what I ended up doing. Length ended up being a bit less than 40 feet. Used the 6-50 outlet required by the welder. Used 8-2 w/ground through underground flex conduit and mounted the outlet high on the wall right next to garage door; ie to encourage outdoor usage. Put in a 30 amp breaker. While maybe not 100% in agreement with all; I figure it should be very safe. It meets s 630, and if someone plugs in something that's drawing more than the wire can support continuously; the breaker will trip. If someone wants to put in a bigger load and trips it; they'd be crazy to put in a larger breaker than the wire can support. That's about akin to putting a penny in for a fuse.

Sound like a good, safe compromise that doesn't really violate anything ?

Thanks again for your suggestion(s) / ideas / concerns.

Bob

"I have 30 A receptacles in my garage. There have to be at least 2. Do I have to check out the cable before I plug in a kiln? Seriously, my wife wants a kiln!"

Yes.

Without knowing what they are designed to supply (and more than one 30 amp receptacle on a circuit is a BAD sign) you cannot just use them for a kiln, or any other load.

"I rest my case."

What is so darn hard about checking the circuit?

A 50 amp receptacle on a 30 amp circuit? Something sounds amiss there.

What's the duty cycle of the welder?

"A 50 amp receptacle on a 30 amp circuit?"

Not necessarily.

Breaker rating and things like wire size and device rating are not related on special use circuits in the same way as on general use circuits.

If the receptacle is also being used as a final disconnect (instead of an actual switch, allowed in some cases) it may need a larger rating than the operating rating.

"Without knowing what they are designed to supply (and more than one 30 amp receptacle on a circuit is a BAD sign) you cannot just use them for a kiln, or any other load."

Thanks, In fact, there are two inside and one outside. The outside one was probably for RV or boat use. I understand about more than one on a circuit being a bad design. I have to confess that I have not checked them out yet. I would say it is likely that they are on separate circuits due to the location of the panel (100 amp) and the outlets. (There is no economy to running them in a string.) Since I recently found some 240V open splices where baseboard heaters were removed, I guess I can't take anything for granted. The sad thing is that the former owner was an electrician.

"The sad thing is that the former owner was an electrician."

Not at all unexpected. The best auto body repairman in town often drives a car covered in primer. And many a good carpenter lives in a half finished house.

And let us not forget the cobbler,
his kids go bare foot.

I am new here and joined due to this particular discussion. I am an electrical contractor and recently bought a miller thunderbolt ac dc stick welder that I plan on wiring a receptacle for. The cable feeding the unit is only #10 AWG 3 conductor with what looks to be a 30 amp cord end attached (could have been added later--I bought it used. The welder input power is listed at 240 volt 46 amps if I remember right. My plan was to run #6 AWG wire and terminate to a 50 amp 3 wire twist lock receptacle. I would also replace the male cord end and wire on the welder to #6 wire and a different 50 amp cord end.

The fella named rcmjr had a good question. He asked what size wire should I run for a 50 amp circuit? Well typically without considering Art 630 of the NEC we would run #6 THHN wire to the receptacle unless special circumstances are present such as a long run (over 100 foot), or it is feeding a motor or other instance. If you wanted to go what I would consider "over and above" and leave the receptacle in the home after moving out wired correctly thats how I would run it. That way when so and so moves in and plugs their 45 amp device into the unit they would be safe.

A circuit breaker is kind of like a thermostat. It senses heat and opens the circuit. The problem with art 630 is that if you run #10 wire from a 50 or 60 amp breaker and terminate onto a 50 or 60 amp rated receptacle someone could theoretically come by and plug something other than a welder with a low duty cycle and the WIRE WOULD MELT BEFORE THE BREAKER TRIPPED!!! the size and rating of the insulation of copper wire is listed in 310.16 or thereabouts in the NEC. We usually size wire using the 75 degree column since most panel lugs are only rated for 75 degrees Celsius. That puts you right at about 30 amps.

Now art 630 says I can run #10 wire to my receptacle to feed my 46 amp welder. What it does not say (but I believe it is implied) is that same wire will be terminated into a receptacle and breaker greater than the 30 amp rating of that wire. There are a couple problems with this. But perhaps most frightening is the fire risk. You can either terminate into a 30 amp receptacle for instance or say a 50 amp one. Well, in my opinion it is safer on a higher ampere rating receptacle because the receptacle is rated for a higher ampacity and would not be the weak link in the circuit. Since people who write code do their research I feel safe doing so as long as I prevent unauthorized access to the receptacle and if I was to move I would simply remove it or install a 240 volt 30 amp twist lock receptacle thus providing a safe circuit in most instances.

The ideal situation would be to run wire rated for the amp draw of the machine regardless of what art 630 in the code says about duty cycle and downsizing conductor size. That would mean running #6 to a 50 amp plug and terminating into a 50 amp 2 pole breaker. Or #4 onto a 60 amp breaker and receptacle.

I will probably run #10 wire though to my welder and remove the receptacle and pull the wire off the breaker if I move. I am new to welding but I am comfortable with electricity so I hope that helps someone out.

I am new here and joined due to this particular discussion. I am an electrical contractor and recently bought a miller thunderbolt ac dc stick welder that I plan on wiring a receptacle for. The cable feeding the unit is only #10 AWG 3 conductor with what looks to be a 30 amp cord end attached (could have been added later--I bought it used. The welder input power is listed at 240 volt 46 amps if I remember right. My plan was to run #6 AWG wire and terminate to a 50 amp 3 wire twist lock receptacle. I would also replace the male cord end and wire on the welder to #6 wire and a different 50 amp cord end.

The fella named rcmjr had a good question. He asked what size wire should I run for a 50 amp circuit? Well typically without considering Art 630 of the NEC we would run #6 THHN wire to the receptacle unless special circumstances are present such as a long run (over 100 foot), or it is feeding a motor or other instance. If you wanted to go what I would consider "over and above" and leave the receptacle in the home after moving out wired correctly thats how I would run it. That way when so and so moves in and plugs their 45 amp device into the unit they would be safe.

A circuit breaker is kind of like a thermostat. It senses heat and opens the circuit. The problem with art 630 is that if you run #10 wire from a 50 or 60 amp breaker and terminate onto a 50 or 60 amp rated receptacle someone could theoretically come by and plug something other than a welder with a low duty cycle and the WIRE WOULD MELT BEFORE THE BREAKER TRIPPED!!! the size and rating of the insulation of copper wire is listed in 310.16 or thereabouts in the NEC. We usually size wire using the 75 degree column since most panel lugs are only rated for 75 degrees Celsius. That puts you right at about 30 amps.

Now art 630 says I can run #10 wire to my receptacle to feed my 46 amp welder. What it does not say (but I believe it is implied) is that same wire will be terminated into a receptacle and breaker greater than the 30 amp rating of that wire. There are a couple problems with this. But perhaps most frightening is the fire risk. You can either terminate into a 30 amp receptacle for instance or say a 50 amp one. Well, in my opinion it is safer on a higher ampere rating receptacle because the receptacle is rated for a higher ampacity and would not be the weak link in the circuit. Since people who write code do their research I feel safe doing so as long as I prevent unauthorized access to the receptacle and if I was to move I would simply remove it or install a 240 volt 30 amp twist lock receptacle thus providing a safe circuit in most instances.

The ideal situation would be to run wire rated for the amp draw of the machine regardless of what art 630 in the code says about duty cycle and downsizing conductor size. That would mean running #6 to a 50 amp plug and terminating into a 50 amp 2 pole breaker. Or #4 onto a 60 amp breaker and receptacle.

I will probably run #10 wire though to my welder and remove the receptacle and pull the wire off the breaker if I move. I am new to welding but I am comfortable with electricity so I hope that helps someone out.

My Miller Thunderbolt XL 225/150 AC DC came from the factory with a 12/3 SPT cord and a Nema 6-50 Plug cap. I use it all the time with a 50 foot, 10 gauge extension cord, with no problems. Although I usually weld at around 125 amps I have welded heavy material at 200+ amps AC and the cord didn't get hot at all. I believe the owner's manual specifies a 10 gauge extension cord.

According to Article 630 what conditions must be present to be able to use the #10?

BusDriver let's take a closer look at the article in the NEC. It basically states that if it is only one welder you are feeding and it is an arc not a spot welder you may multiply the listed max amps on the nameplate of the welder by a multiier shown in table 630.11(A). In my case 20% duty cycle is listed as .45. So 47.5 (X) .45 = 21.5 amp rated wire. Now we have to go to table 310.15(B)(16). I was taught if you are sizing wire under 100 amps to use the 60 degree column which shows #12 good for up to 20 amps and #10 good for up to 30 A. But my 2011 NEC handbook shows an exams using the 75 degree column so let's use that. This comes to a minimum of #12 conductors (THHN).

630.11 basically let's you size your over current protection (circuit breaker) at 200% of the maximum primary amps listed on your welder. So for my welder I can actually use a breaker up to 200% the rating of my rated primary amps on the welder (47.5) which would be 95 amps. The code allows the next biggest size so that would be a 100 amp breaker. That is the maximum in practice I would never need one that big for my buzz box.

Sounds crazy!! 100 amp breaker with #12 conductors!!!! It wouldn't happen since you would also be required to use a 100 amp receptacle (not all tha common). For my welder I will run #10 wire from a 30 amp breaker and land it on a 30 amp 3 wire twist lock receptacle. I will also install #10 type SO cable to the switch on my welder and put a 30 amp twist lock cord end on be cable. I hope it doesn't trip the 30 amp breaker. If it does the code allows me to go up one breaker size to the next common size to prevent undesired operation. Or I could just put a 50 amp receptacle on number 10 wire protected from a 50 amp breaker. This is probably the standard practice for most small 240 volt welding machines (I am a new welder but have wired a few).

Disclaimer: the stuff I wrote is for informational purposes only and you and you only are responsible for the work you do electrically. I take no responsibility for any fires or other undesired effects of advice given here.

Article 630 states that the ampacity of the supply conductors shall not be less than the I-1 eff value on the rating plate, if given. If not given, it goes on to say to use the rated input amps off the rating plate and table 630.11(A) for a single nonmotor generator machine. The instructions provided with the Thunderbolt also follow table 630.11(A). Note however that the instructions say to install the conductors in conduit "or equivalent", which seems to disallow a cable type of wiring method. Article 630 does not contain this requirement.

This post was edited by joefixit2 on Thu, Jan 23, 14 at 23:51

"According to Article 630 what conditions must be present to be able to use the #10?"

630.1 Scope says "".....equipment that is connected to an electrical supply system"

This could be interpreted at hard wired, not plug and cord. It is clear as mud.

Thanks JoeFixit.

I am by no means always right. The directions online for my model and serial number thunderbolt are a bit vague since it is really old. It does not give a wire size or I overcurrent protection size. The nameplate on my welder does not give an I eff rating. Does yours? Was I incorrect in string that 630 says I could use a 100 amp breaker then (200% primary listed current)??? It seemed you were implying I was wrong.

As far as not running Romex or MC cable I've been doing this quite a while and nowhere I've seen in the code prevents me from wiring a welder with this type of wire. I am going to go with the NEC over the directions of the welder as far as running pipe or running MC or BX. You don't want to run romex Down the surface of a wall without protection but mc cable would be fine this way. Romex in a wall cavity in a residence is also acceptable. Seems
to me Miller might be saying in essence to make sure your wire is protected for damage but I may be mistaken.

Hey Joe,

I believe you are wrong stating that 630.1 restricts the use of a cord an plug connected welder and/ or it's application upon such equipment. Your clock radio is "connected to an electrical supply system" by means of a cord and plug. Are you saying that article 630 does not apply to welders connected by a cord to a receptacle? This is simply not the case.

Jimmy,

I am not saying anyone is wrong or right, I am just putting whatever info I can find out there for discussion. I agree with you that a plug and cord connection qualifies as "connected to an electrical system", but was pointing out how vague the code is and how it could be interpreted differently by different people.

You are correct that the code does not prohibit you from running NM wiring, it is the instruction manual that came with my Thunderbolt that instructs conduit to be used.

My Thunderbolt does not give the I-1 eff value, just the supply amps at full power (47.5 input amps at 225 AC welding amps)

Article 630 has always interested me and not a lot of people are familiar with it, although it is such a short and simple article (as simple as any NEC article can be anyway!). I have always thought in the back of my mind the same thing Speedy Petey brought up in the earlier posts (this thread is nearly 3 years old) about creating a receptacle circuit that is open to misuse by untrained persons without them even realizing the danger. I feel that table 630.11(A) should probably be restricted to hard wired machines only, and probably should not apply at all in residential installations.
Then I see Brickeyes point as well, trying to predict the future of our installations would be never ending.

Happy welding and be sure to check out the Welding Web forums!
www.weldingweb.com/