Bizare welding receptacle question

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SceneryDriver

Senior Member
Location
NJ
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Electrical and Automation Designer
Hi All,
My company is moving into a new shop building, and as we've been setting up, we discovered the EC did something strange with the receptacles meant for our MIG and TIG welders. I'm fairly certain I've identified the code violation(s) that we can hang our hats on in order to request a fix, but I wanted to run it by the brain trust here.

Here's the situation:
(3) separate shop areas; Metalworking, Assembly/Carpentry, and Machine Shop.

In the Metalworking area:
(6) 6-50 straight-blade receptacles, all on (1) 80A 2-pole breaker #4 CU THWN supply conductors, #6 taps at the receptacle, splices with split bolts and tape.

In the Assembly/Carpentry area:
(7) 6-50 straight-blade receptacles, all on (1) 50A 2-pole breaker. Unsure on supply conductor size; I haven't been in those boxes yet.

In the Machine Shop:
(6) 6-50 straight-blade receptacles, all on (1) 50A 2-pole breaker. Unsure on supply conductor size; I haven't been in those boxes yet.


Code violations I believe I've identified (assume 2011 code)

-630.11(B) Minimum conductor ampacity shall
be based on the individual currents determined in 630.11(A)
as the sum of 100 percent of the two largest welders, plus
85 percent of the third largest welder, plus 70 percent of the
fourth largest welder, plus 60 percent of all remaining welders.

Even in the Metalworking Area, which is fed from an 80A breaker, we can easily find ourselves operating (4) welders at a time. Based on the draw of our welders, and the math in 630.11(B), we exceed the ampacity of the supply conductors for the circuit (#4 CU, THWN). That said, we'd trip the 80A breaker as well.



-Table 210.21(B)(3) Receptacle Ratings for Various Size Circuits

Circuit Rating (Amperes)Receptacle Rating (Amperes)
15Not over 15
2015 or 20
3030
4040 or 50
5050

At least in the Metalworking area, the receptacles, rated for 50A, are fed from an 80A circuit.


I believe the j-boxes with the split-bolt splices are over-filled; I had a devil of a time getting the receptacle I pulled for inspection back into the box. I will do the wire fill math tomorrow and get back to the thread. Incidentally, how does one account for the considerable bilk of split bolts and tape when doing wire fill calcs?

I know the NEC isn't a design guide, and you can do dumb things that aren't a violation, but these welder outlets seem to be a screw-up on the part of the EC. Especially in the Metalworking area, where they're fed from an 80A breaker. Please let me know if I've missed a code violation, or if I'm off in the weeds. We'd like to try to find a violation or two to strengthen our case with the EC that it's their problem to fix, not ours.



Thanks!

SceneryDriver


edit: formatting
 
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You had me at split bolts....

Seriously though, if it were me I typically quiz people pretty hard on what they run in their shops and try to find out what kind of loads I expect to have to supply power for.

If you are running 4 welders at once I would have just pulled 4 separate circuits. I'm not one for tapping unless it's panel feeders.
I'm pretty sure you aren't supposed to put a 80A breaker on a 50A recep.
 
Without the rating plate numbers it's difficult to comment on the wire sizes and OCP size. Because of the exception in 210.21 for welders, the receptacle can be rated less than the overcurrent protective device.

As far as box fill, keep in mind if #4 conductors are involved, volume is not the deciding factor. 314.28 becomes you guide,. not 314.16. If the job is in ciompliance with 314.28, the split bolts would likely not be a problem.
 
augie47 said:
Without the rating plate numbers it's difficult to comment on the wire sizes and OCP size. Because of the exception in 210.21 for welders, the receptacle can be rated less than the overcurrent protective device.

As far as box fill, keep in mind if #4 conductors are involved, volume is not the deciding factor. 314.28 becomes you guide,. not 314.16. If the job is in ciompliance with 314.28, the split bolts would likely not be a problem.
Click to expand...
I agree, this install may actually be NEC compliant. Nameplates and box/raceway size details must be known before we can call anything a violation.
 
As far as tripping the 80 A breaker in the Metalworking area, my reading of 630.12(B) is that the #4 in question could be behind a 175 A breaker and be Code compliant. Unless I am missing something and may well be.

Ben
 
mwm1752 said:
Agree, do not know what was previously used in the shop prior to your move.
Click to expand...


The building is actually newly built, just for us. As it turns out, it's a moot point. The Boss is going to take it to the contractor and have the receptacles placed on their own breakers; while it might be code compliant, he agrees with me that it's a dumb design and we are going to have it changed. As to who pays for it, that's thankfully well above my pay grade.

Thanks!


SceneryDriver
 
Great, prop guys deciding something they don't know about is 'dumb'. :D

Well good for the EC that gets paid to fix what is not broken.:)

The key is duty cycle and understanding your shops don't all weld continuously, at the same time at full current settings.
 
Actual draw on welders ??

Actual draw on welders ??

In a typical machine shop; a welder rarely gets close to nameplate amperage, unless they are using spot-welding ,or, using sub-arc's, or large scale fill. The amp draw is typically less than what a person might think.

I have seen many welders run rod/Migs all day and never trip a 2-pole 30amp breaker.
 
SceneryDriver said:
The building is actually newly built, just for us. As it turns out, it's a moot point. The Boss is going to take it to the contractor and have the receptacles placed on their own breakers; while it might be code compliant, he agrees with me that it's a dumb design and we are going to have it changed. As to who pays for it, that's thankfully well above my pay grade.

Thanks!


SceneryDriver
Click to expand...
Who designed it and was it done to the design specs, or was it design as you go?
 
kwired said:
Who designed it and was it done to the design specs, or was it design as you go?
Click to expand...

I believe it was the consultant/architect. It wasn't caught by anyone at design review time. There's plenty of FUBAR to go around. The EC is landing a subpanel and running the necessary circuits and pipe.



SceneryDriver
 
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