Welder Control Panel Wiring

H

holysmartone

Member
Location
Michigan
Occupation
Controls Engineer
Hello all! Let me start out by saying that I am junior controls engineer. I have been doing panel designs and builds for a few years now. I normally work in low power situations, just simple control panels with 24v circuits and a couple amps of 480v to power a robot or two. My new job has me designing a panel with more power than I've ever worked with before, and has me struggling.

I am building a panel for a automated projection weld machine. My question comes from the wiring for the welder. The manufacturer recommends a 160amp circuit breaker, so I have one of those designed in. When it comes to the wiring, my NFPA chart tells me that for 160amps I would need to use 3/0 wire at 60 degrees. If that is true, why does the manufacturer supplied control cabinet for the welder only use 2 AWG? The manufacturer also recommends 2 AWG for up to a 10 meter pull to the controller. Isn't this wire undersized? Or is the manufacturer doing something to derate the wire based on the max 20% duty cycle?

Looking for any help you guys can provide. I would greatly appreciate it.
 
A lot of it is about the welder duty cycle- if the welder is only used or rated for a lower duty cycle, Art. 630 allows a smaller wire than you'd expect for a continuous load because it has a chance to cool off during the non-use time.

Take a look at some of the other topics for welder circuits in these forums and also at 630.
 
Art 630 is interesting when you look at duty cycle. A little buzz box welder may have a 20% duty cycle meaning it can be used 2 minutes out of every 10. So the branch ckt wires are much smaller than would expect
 
Looked it up, and projection welding is similar to spot welding, the current is high, but for a very short period of time. I had one that was on a 200 amp 480 breaker, but only called for #2 cu. I had already ran 2” pvc, because the manufacturer said not to use metal conduit. If I had known beforehand, I would have run smaller conduit, as the conductors were slapping inside the conduit due to the high electro magnetic force.
 
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