Welder branch circuit sizing?

whoaru99

Epic Member
Sometime in the coming weeks I'm going to help a buddy put in a dedicated circuit for a simple AC/DC buzz-box style stick welder.

The nameplate on the welder says 42A max primary current at 20% duty cycle rating. The welder power cord has a 6-50 plug (50A - 250V, uses two hots and grounding wire).

According to my interpretation of NEC section 630 re. arc welder, the 42A can be derated by 0.45 due to the 20% duty cycle rating. This gives 19A in round numbers so it looks like I could use 12ga wire, but will go up to 10ga just because.

Then, for the breaker, NEC 630 also seems to say for a dedicated welding circuit you can install overcurrent protection up to 200% of the conductor rating. For 10ga wire that means up to 60A. However, it still appears the overcurrent protection can't be more than 50A due to the receptacle rating.

With all considered, it looks like the install would be fully Code-compliant if we put in a 6-50R receptacle, wired to a 50A breaker, using 10-2 w/ground cable.

Looks correct?
 
I'm not an electrician but I play one on TV. Looks like you're on the right track...not overly conservative but should get the job done safely.
 
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