1st post for me here. I am installing a arc welder which calls for in it's litature using art. NEC 630-11 a OCPD @ 150 amps and conductor @ #4 (95 amps @ 90c table 310.16). The welder is single phase with a # 6 cord and a 50 amp plug. I ran the #4, but put in only a 50 amp OCPD backing up the 50 amp cord non fused disc. Duty cycle is 60%
My questions; Why do they use 90 c column, most OCPD's and devices are 75c? Should I have replaced the factory cord with 100 amp and direct wire with a disconnect or sell the cust a 100 amp cord, plug and recept.? OR just slap in a 150 amp backing the 50 amp recept! What if a different piece of equip is plugged in that location.
The little extra amperage you can use for derating purposes like for wire count in conduits and ambient temperture corrections.
Welders wired under provisions of Article 630 Cord can use derate wire sized based on its duty cycle. The thought is with a 60% duty cycle meaning it is not to ran no more the 36 minutes per hour(60% of an hour). Even if the welder is cranking out 100 amps which will be rare with you welder if properly sized for the work, the cord will not get hot enough to cause damage. Besides the cord is part of the equipment which is not covered by the NEC. The outlet though is a different story. In theory, some other piece of equipment could be pluged in the the receptacle. The circuit must be able to carry the load.
The welder should be wired per the maufacuter's instuction. Failure to do so can void warranty and listing. If you void the listing, you can not use it. NEC requires all electrical components be listed or approved by a third party tester facility such as UL. That is why you see the little stamp like on a 4" square blank cover. Although it is just a square piece of metal, it still must be listed.
Flexible cables for cords use table 400.5(B). #6-2 90°C Type W is rated for 99 Amps.
Personally, if it's cord-and-plug, I'd size OCPD for the cable & plug, too, regardless of what 630 says, because *anything* could be plugged into that receptacle. The breaker is designed to mimic cable heating, so (in theory) it shouldn't trip prematurely if the welder's duty cycle is OK for a 50A plug, even if current exceeds 50A.
thanks for your thoughts guys. I knew I came to the right place.
Right now I have a 50 amp OCPD, and watching how she does with the work. I'm not comfortable going up in size with the OCPD unless I change out the receptacle and plug to maybe just a disc. I know we size motor discs, plugs and recept's and to FLA and HP. That's EZ. Perhaps I'll call the mfg. I know we upsize OCPD for inrush on a still rotor with a motor. I'm wondering how the welder does on initial amps with that 50.