Resistance Welder

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Nitty

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I am moving some spot welding equipment and am questioning the present installation. Example; Spot Welder 480Volt, Single Phase, 150KVA, 80' from distribution panel. Presently it is being fed with 2) 500 KcMil Copper conductors and a 400 amp breaker. After reviewing NEC 630.31 It seems that the ampacity of the circuit conductors shall not be less than 50% of rated primary current, which means I could refeed the spot welder with 2/0awg Copper (175 amps) provided the distance wouldn't require voltage drop derating, and simply reuse the 400 amp breaker for overcurrent protection. Is there something I may be overlooking?
 
If it's resistive, non automatic and not a seam welder, I would say you were correct, but I would encourage you to investigate further.
 
It is not a seam welder, and is non-automatic. I talked with the operator and found that the duty cycle is quite low. Since full load current would be present on conductors for only a fraction of operation time the conductors would incur a fraction of heat loading thereby allowing the reduction in conductor size.
 
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