my buddy just bought a miller tig welder and wants me to run a circuit for his welder. i was checking out the owners manual and it recommends using a 80a breaker w/ 8awg copper conductors. should i up the wire size to 6awg or go with the manufacturers recommendation?? anyone w/ experience hooking up welders?? i looked in 630.11 but couldn't interpret it.
[img][IMG]http://img104.imageshack.us/img104/9372/millerzj1.th.png[/img][/img]

You should be fine with the manufacturer's recommendation.
It looks like they've just taken into account the duty cycle of the welder and applied the proper multiplier.

Looking at the specs it says:
Min Grounding Conductor #8
with a footnote (4) size per 310.16

Why would they size the EG using 310.16?
Why do they call for the EG to be the same size as the current carrying conductors? Extra safty or a mistake?
I would say it should be sized per 250.122.

Also it lists the unit as:
Drawing 54 amps at rated output
Use #8 min input conductors
With the same footnot size per 310.16

If I look at 310.16 #8 is good for 55 amps if you could use the 90 degree column. In the 75 degree column it is only good for 50 amps.

I agree you can derate it for duty cycle per 630.11.
It does not list the duty cycle on this page. And still why would they say size per 310.16 with no mention of derating. Would derating the conductors per duty cycle be concidered by some as failing to follow manufactures instructions.

To me it just looks like the manufacture stumbled with the NEC when printing the manual.

Stick with the owners recommendations. They know what the equipment needs better than anyone. I'm sure they didn't guess at wire size of grounding requirements. Unfortunately everything in life will not make sense.

On the other hand... oversizing the feeder will only harm the owner's wallet. Technically it will increase the life expectance of the wire since the insulation temperature will be lower. And NO, I'm absolutely not sure if the people printing a tech manual really know what they're doing.

Kojunho,
Just curious of the model of the Miller Tig. I would like to read the manual. I looked at a couple of Maxstar models on the website. The manuals seem to be on the money with ground and sizing recommendations. It seems like like the sizing recommendation in your post is based on motor sizing rules. I have hooked up welders and used to clean the Miller hard-wired welders at my last shop. Really wierd, but with todays technology anything is possible.

Would it be a violation to use #8 awg on a 80 amp breaker?
60c wire max is 40 amp column 1
75c wire max is 50 amp column 2
90c wire max is 55 amp column 3
No derate calculated.

The equipment conductors can be whatever the manufacturer wants to use. As they calculate at diferrent wire temps.

If it were my welder, I would use a 60 amp breaker with #6 wire and 90c or 75c wire. My first thought was a 50 amp breaker but your load is 54 amps.

The manufacturer may be considering the high inrush current when you start welding. (thus 80 amp breaker)?

The manufacturers care nothing about the code. What you do for the hook up is in your lap, not theirs.

Welders are in article 630. The rules allow fairly small conductors for a low duty cycle welder.
You can never go wrong using 310.16 but that will be more wire than you need in most cases, particularly for the typical homeowner welder. I used 310.16 for mine but I knew I might be using that outlet for other things, another consideration when you turn Harry Homeowner loose with an extra circuit.

the welder is a miller syncrowave 200. im thinking about using the time delay fuses instead of the 80a breaker. 80a breakers aren't easy to find. by the time i get home the supply houses are closed. if i hook it up using the 60a time-delay fuses, would i still run 8awg from the panel to 60a time-delay disconnect, and use a 40a breaker in the sub-panel?? my foreman tells me to run 6awg but want to see what others have to say

The characteristics of the welder itself will not be changed.
The wire size will remain the same with the exception of the equipment grounding conductor, which with a 60A overcurrent protection could, by NEC, be reduced to a #10.

You've just had an easy hundred or two years of combined experience explain this to you.

Are you sure you want to put that 40Amp breaker in the subpanel? You've now gone from a matter of the manufacturer's recommendations at 80A OCPD with #8 to a 40A OCPD with #6??

Does your foreman have any reason that he can cite for the increased conductor size to #6? That's just nonsense.

sorry i probably didnt explain it clearly. but if you click on the image again it gives two choices on hooking up the welder.
-60a time delay fuses with 8awg conductor
or
-80a breaker with 8awg conductor

i couldnt find a 80a breaker so i want to use the 60a time-delay fuses. my question was, from the sub-panel to the 60a time-delay disconnect, can i use 8awg with a 40a breaker to feed the 60a time-delay disconnect??

thanks for your guys advice....

Kojunho, you are reading the chart incorrectly

The table you posted shows subnote (1) for circuit breakers
"Consult factory for circuit breaker applications"

Subnote (2) for Time delay Fuses recommends 60Amp fuses.

Subnote (3), which is the one that you keep referring to, is not for circuit breakers, it's for Normal Operating (non delay) Fuses, and is where you are getting your 80 Amp figure from.

Simply put, a welder with a 54 amp load will not work reliably, when turned up, on a 40 Amp breaker. A 60 Amp time delay fuse will not serve any purpose whatsoever when fed with a 40 Amp breaker.

You should call Miller, see what they recommend for a circuit breaker size, and then follow their instructions.
The same goes for the conductor sizing.

Just a little anecdotal experience. I have a 230a "buzz box" that said it should be on a 48a breaker (unobtanium). Since I didn't have any easy way to put in another circuit when I bought it about 37 years ago I just put a dryer plug on it and plugged it into the 30a circuit my dryer was on. It has never blown a fuse or tripped a breaker and I still run it on 30a circuits.
I may have never used it on the highest setting with the biggest rod it will handle, using it at the maximum duty cycle but I doubt anyone else does either.