Yeah, me too....
Required wire size for 220v welder
- Thread starter KillNThrill24
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Yeah, me too....
sberry
Banned
The original question was,, what wire required. I believe in this case it is 14 but limited to a 30A breaker with the minimum wire. Whoops,,, I could be wrong,, not sure of the particular machine. The new Miller's in that class do.
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ssdave
Banned
We're beating a dead horse: but, to answer the original question, let's go to the information given, the code requirement, and wire ampacity.
The information given is it's a welder with 25% duty cycle, and manufacturer recommendation of 50 amp breaker.
First way is to assume manufacturer has sized max breaker to correspond with actual machine max current.
From ampacity chart below, for NM-B cable, 50 amps requires #6 copper wire. So, from a strict non/exception standpoint, you would install a 50 amp breaker, and 6 ga copper NM-B. If you installed conduit, and 90 degree wire, you could go to 8 ga copper.
However, the NEC Article 630.11 allows derating conductors for welding circuits, based on duty cycle. for 25% duty cycle (interpolate between 20% and 30% duty cycle), a 50% derating is allowed. So, the 50 amp circuit could be derated to 25 amp. This would allow 10 ga NM-B to be used, or 14 ga 90 degree THHN in conduit. The breaker can remain the same as the un-derated value, or 50 amps. In fact, the code will allow the breaker to be upsized one size if nuisance trips occur. However, the code also limits breaker size to 200% of derated wire ampacity. So, the 50 amp max breaker would be required. Of course, a smaller breaker could be used, but could result in nuisance tripping.
Now, the question comes up of what is the real max current draw of the welder? It is likely less than the breaker recommendation, as the manufacturer probably took into account some of the derating in code in their recommendation. If it is actually less than the manufacturers breaker recommendation of 50 amps, then the calculations would need to be run again with the real current.
So, the OP's decision to go with 8 ga NM-B wire, is code compliant and slightly conservative for a welder circuit that could be derated to 10 ga.
Given the constraints that sberry has put on his installation recommendation, he could use 14 ga THHN in conduit, and meet the letter of the code for a derated welder circuit. However, the 30 amp breaker he recommends might be subject to nuisance trips, and could be upsized to 40 or 50 to eliminate nuisance trips and still meet code.
The information given is it's a welder with 25% duty cycle, and manufacturer recommendation of 50 amp breaker.
First way is to assume manufacturer has sized max breaker to correspond with actual machine max current.
From ampacity chart below, for NM-B cable, 50 amps requires #6 copper wire. So, from a strict non/exception standpoint, you would install a 50 amp breaker, and 6 ga copper NM-B. If you installed conduit, and 90 degree wire, you could go to 8 ga copper.
However, the NEC Article 630.11 allows derating conductors for welding circuits, based on duty cycle. for 25% duty cycle (interpolate between 20% and 30% duty cycle), a 50% derating is allowed. So, the 50 amp circuit could be derated to 25 amp. This would allow 10 ga NM-B to be used, or 14 ga 90 degree THHN in conduit. The breaker can remain the same as the un-derated value, or 50 amps. In fact, the code will allow the breaker to be upsized one size if nuisance trips occur. However, the code also limits breaker size to 200% of derated wire ampacity. So, the 50 amp max breaker would be required. Of course, a smaller breaker could be used, but could result in nuisance tripping.
Now, the question comes up of what is the real max current draw of the welder? It is likely less than the breaker recommendation, as the manufacturer probably took into account some of the derating in code in their recommendation. If it is actually less than the manufacturers breaker recommendation of 50 amps, then the calculations would need to be run again with the real current.
So, the OP's decision to go with 8 ga NM-B wire, is code compliant and slightly conservative for a welder circuit that could be derated to 10 ga.
Given the constraints that sberry has put on his installation recommendation, he could use 14 ga THHN in conduit, and meet the letter of the code for a derated welder circuit. However, the 30 amp breaker he recommends might be subject to nuisance trips, and could be upsized to 40 or 50 to eliminate nuisance trips and still meet code.
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sberry
Banned
That's a good post,, but,, it's not my reccomendation. It's the requirement. I don't use the smallest wire, it's just the code and in the instruction manual. I have never wired one with 14. I have wired a couple new small machines 12 with 30 but have wired a lot of buzzers 10 as did thousands and thousands of other electricians when these machines became popular in small garages.
Back in the day when fuses were the norm garages had 60A entrance, they used the feed thru with 10 to 1 arm bandits for compressors, lots of times mechanic comps, 3 hp and used the "range" side of the panel with 50A fuses and 10 cable to a welder outlet. I still remember replacing one in my Dad's farm shop, have seen them elsewhere and they were installed by legit electricians.
You could also tell the install was done by trained men as they followed the staple requirements.
Back in the day when fuses were the norm garages had 60A entrance, they used the feed thru with 10 to 1 arm bandits for compressors, lots of times mechanic comps, 3 hp and used the "range" side of the panel with 50A fuses and 10 cable to a welder outlet. I still remember replacing one in my Dad's farm shop, have seen them elsewhere and they were installed by legit electricians.
You could also tell the install was done by trained men as they followed the staple requirements.
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dr_clyde
Well-known member
My shop has a few 50 amp circuits, used mostly for a welder, occasionally a plasma cutter or some other non-motor related activity.
I have #8 THHN in conduit, wired to 50 amp breakers. Installed by a licensed electrician to code.
My Syncrowave 350 takes a 100 amp breaker, and is hard wired to the panel with #2 conductor cord.
All my motors (save for a couple 120V) are on either 480V or 208V 3 phase, and are run on separate circuits, the high voltage stuff is on fused disconnects.
You could probably get away just fine with #10, but for the very minimal cost difference, why wouldn't you use #8? Then you're covered if you want to run a small heat treat oven, big compressor, or just a couple loads on a single circuit.
I have #8 THHN in conduit, wired to 50 amp breakers. Installed by a licensed electrician to code.
My Syncrowave 350 takes a 100 amp breaker, and is hard wired to the panel with #2 conductor cord.
All my motors (save for a couple 120V) are on either 480V or 208V 3 phase, and are run on separate circuits, the high voltage stuff is on fused disconnects.
You could probably get away just fine with #10, but for the very minimal cost difference, why wouldn't you use #8? Then you're covered if you want to run a small heat treat oven, big compressor, or just a couple loads on a single circuit.