1 Ph Welder on 3 ph panel - panel sizing

[W6SJK]

Example: Lincoln TIG 255 Arc Welder single phase arc welder rated 81/58/41 amps at 40/60/100% duty cycle respectively, 208/1/60. Assuming 40% duty cycle, NEC 630.11(A) says take the 81FLA x 63% giving 51A min conductor ampacity. For group installations 630.11 (B) says take the first 2 at 100% and 85% for the 3rd, 70% for the 4th, 60% for the rest.

I have 9 welders on a panel...
51+51+(51*.85)+(51*.70)+(5*51*.6) = 334A which would be for a single phase panel.

Now if I have 9 welders on a THREE PHASE panel, 334A would not be correct, since the load is balanced on three phases. The panel would be way oversized. What does the NEC require for panel and feeder ampacity? Divide by 3, then multiply by sqrt (3)?

 

[One-eyed Jack]

Example: Lincoln TIG 255 Arc Welder single phase arc welder rated 81/58/41 amps at 40/60/100% duty cycle respectively, 208/1/60. Assuming 40% duty cycle, NEC 630.11(A) says take the 81FLA x 63% giving 51A min conductor ampacity. For group installations 630.11 (B) says take the first 2 at 100% and 85% for the 3rd, 70% for the 4th, 60% for the rest.

I have 9 welders on a panel...
51+51+(51*.85)+(51*.70)+(5*51*.6) = 334A which would be for a single phase panel.

Now if I have 9 welders on a THREE PHASE panel, 334A would not be correct, since the load is balanced on three phases. The panel would be way oversized. What does the NEC require for panel and feeder ampacity? Divide by 3, then multiply by sqrt (3)?

That would give you 192 amps per phase. Or you could convert to watts and divide by LLx1.73 which would also be 192 amps. Looks good to me. I don't see a ref. to a 3 phase application.