TIG Welder Wiring Question

[Graham08]

I am at the point in my shop build where I'm starting to plan out my wiring. The biggest load in my shop will be my Lincoln Precision TIG 275 welder, which is rated by Lincoln at 95A input current (@ 230V) for the 275A ouput current, and 40% duty cycle.

I'm thinking I want to:

1. Use a 100A breaker in the main panel. (I have 200A service in the shop)
2. Run #2 copper from the panel to a 100A disconnect. (Surface mounted in either 1" or 1-1/4" EMT, about a 20' run)
3. Use #4-3 SOOW cord to connect the welder to the disconnect. This would be about a 10' run of cord, mostly to allow the welder to get pulled out to clean, swap argon bottles, etc. It's on the Lincoln rolling chassis, so I have to allow for some movement.

First, is this kosher as far as the NEC is concerned? I am a little unsure of how derating for duty cycle works.

Second, would you guys do this differently?

And, I almost forgot...do I want a two or three pole disconnect? I am assuming two because this is single phase.

Thanks!

 

[sberry]

You have the owners manual for this? There is electric service guide for it. I suspect you are pretty close in a guesstimate for the wire sizes. If I had 2 I would use it, if I was able to use a 4 cord I might go 3 if I had to buy wire. Miller lists their manuals on line, not sure about Lincoln.

 

[Graham08]

Yes, I have the manual. It's been so long since I've looked at it that I don't remember if it gives any guidance on wiring other than the input voltage and current requirements.

I've been running the machine on a 50A circuit since I bought it new several years ago, and have never tripped the breaker, so I'm not maxing it out by any stretch. I figured since I'm building new, and have to wire it anyway, I should go ahead and make sure I've got the full capacity of the machine available if needed.

I will check the manual.

 

[sberry]

Yes, you will be good to go with either 2 or 3 especially at home, even 3 allows for running it beyond its rated output. As a home brew deal the 4 will be fine for a cord also.

 

[Naq]

Ampacity is calculated using a multiplier from the table based on duty cycle. So 95A@40% duty is 95A x 0.69 = 66A effective

#4CU is good for 70/85A in the 60/75C columns depending on the installation.
#4SO cord is good for 70A as well.

Overcurrent protection is allowed up to 200% of rated input current or conductor ampacity whichever is less so 2x95A=190A, or 2x70A=140A allowed to upsize to next standard breaker = 150A branch breaker maximum.

The disconnect is nice to have, but the SO cord will require a plug and receptacle or cord connector.

Feel free to use larger than #4CU and smaller than 150A breaker if you like.

 

[Graham08]

So it is not legal to wire the cord direct into the disconnect?

 

[Naq]

Technically not if it's connected to an appliance or equipment that can be moved. It just came up recently. FWIW

"400.7 Uses Permitted
(A) Uses. Flexible cords and cables shall be used only for
the following:
(1) Pendants
(2) Wiring of luminaires
(3) Connection of portable luminaires, portable and mobile
signs, or appliances
(4) Elevator cables
(5) Wiring of cranes and hoists
(6) Connection of utilization equipment to facilitate frequent
interchange
(7) Prevention of the transmission of noise or vibration
(8) Appliances where the fastening means and mechanical
connections are specifically designed to permit ready
removal for maintenance and repair, and the appliance
is intended or identified for flexible cord connection
(9) Connection of moving parts
(10) Where specifically permitted elsewhere in this Code

(B) Attachment Plugs. Where used as permitted in
400.7(A)(3), (A)(6), and (A)(8), each flexible cord shall be
equipped with an attachment plug and shall be energized
from a receptacle outlet or cord connector body."

 

[sberry]

The man has quoted the code,,, so this is only an opinion,,, if it was mine would wire it to the disconnect due to the fact the hardware (probably get by with 6-50 stuff though) is harder to source and expensive, you are using this in a limited fashion where the control of this installation remains with you. You have 2 means of service disconnect, if I plugged it I wouldn't bother with the second one. I guess I would tend to do this (wiring to disc), no need to leave 50A hardware where someone could assume it is a 50A circuit.
This is an area where it might not follow the letter but certainly meets the intent for safety reasons and not something I would lose sleep over. We see so many cobble jobs this would be way, way down on the list.

 

[Graham08]

FWIW, the manual recommends #4 Cu wire, and a 125A breaker for DC, balanced AC, or 150A breaker for unbalanced AC.

Any suggestions on a 70A plug/receptacle combo?

I would like to do this by the book, but there is a possiblity I would add after the electrical inspection since it is not shown on any of the plans...In which case I would wire the cord direct to a disconnect and be done with it.

 

[Naq]

I do see the intent of the plug or cord connector to keep people from opening potentially energized boxes to disconnect wires on a portable or serviceable piece of equipment, but I don't know how critical it really is. Someone mentioned that the disconnect lugs weren't rated for the fine stranding of the cord wires, but I don't know that either.

Typically fixed equipment wire/cable is pulled through flexible conduit (eg. sealtite, etc...) with fittings on each end.

If you need it to be mobile you're looking at a 100A welding outlet. Something like these guys:
http://www.grainger.com/Grainger/HUBBELL-WIRING-DEVICEKELLEMS-Pin-and-Sleeve-4TAD1?Pid=search

Ouch!

Ultimately your AHJ has the say it what you can/can't do. Anything beyond that is your own comfort/convenience level.

 

[sberry]

On forums we don't recommend people getting past inspections but if it was being surface piped why put it in till its needed? Or a lot of guys may put pipe in and wire later.

 

[Aceman]

I wouldn't use cord. I'd pipe it to a box on the wall next to the welder, and then flex to it. With no extra disconnect other than the breaker feeding the circuit. This way it's a straight shot from the breaker right into the welder with no extra splices, receptacles, etc to possibly fail or wear out.

 

[Graham08]

Thanks for all the suggestions.

Grainger certainly is proud of those 100A plugs!

Here's a picture of the welder in question:

The only real reason for wanting some mobility is to pull it out from the wall to change cylinders and clean under it. It is a 1000+ pound machine with two cylinders on board, so it's not like it's portable.

Inverter welders are looking better all the time, but this one's paid for!

At least now I am aware of the code and safety implications, and can consider my options. I've got some time before I actually have to do the install.

 

[Norcal]

Instead of flexible cord, use sealtite & THHN conductors, complies w/ code & get the flexibility desired, but how kosher it is will depend on the length of the sealtite......

Sealtite is liquidtight flexible metallic or non-metallic conduit, I normally use the non-metallic variety.

 

[Graham08]

I will look into that. If it's flexible enough, I will go that route. I'm trying to keep the length of the flexible section as short as practical, so I should be code compliant.

What you and Aceman have suggested are definitely the lowest-cost options. (No cord, disconnect, or $$$ plugs).