Welder calc question

[Steve McKinney]

Fellas,

630.12 Overcurrent Protection..........................."Where the values as determined by this section do not correspond with the standard ampere ratings provided in 240.6 or the rating or setting specified results in unnecessary opening of the overcurrent device, the next higher standard rating or setting shall be permitted."

630.12(B) For Conductors. Conductors that supply one or more welders shall be protected by an overcurrent device rated or set at not more than 200% of the conductor ampacity.

My question, what if the next "standard size" exceeds 200%? This question came up in class last night and I could not answer it.

Thanks guys,

Steve

 

[BAHTAH]

Welder Calc

Welder Calc

Steve, I have always taken 630.12(b) to mean 200% of the conductor ampacity is as high as you can go with an overcurrent device. This applies to circuits with only one welder or a circuit with more than one welder. An example would be a welder with a 40amp primary rating and a 50% duty cycle. 40amps x .71 (nonmotor generator type)=28.4 amps so you would use #10awg that is rated for 35amps at 75-degc. This would allow you to go as high as 70amps on the primary protective device. On a single welder circuit I cannot remember going more than 125% on the primary protection, I guess on a multiple welder circuit this could be an issue, in which case I think you would need to size the conductors to allow for the possibility of having to use a higher ampacity breaker.

 

[Steve McKinney]

Thnx Grant,

I appreciate your response. Maybe I am reading too much into this. I can see that the conductor ocp will always be less than 200% because of the duty cycle multiplier and we can round up to the next standard size, then double it. Also with arc welders, with nameplate or I/max can be no more than 200% overcurrent protection for the welder. And we would figure that at 100% of nameplate.

I tried working some more examples and never could get it to be a problem. I see what you are saying Grant. I suppose the "not to exceed 200%" in 630.12(B) would take priority over "next higher standard rating shall be permitted" in 630.12.

Thanks for your time!

Steve