load calc ?

[gordonfan]

i am going to add 16 welders to a 480v/800a-3ph mdp. the current load is 73 amps. i am not sure i understand nec 630-11 ? what would my added load be?

16 welders @ 480v/50a-3ph, 70% duty cycle.

 

[gordonfan]

would this be correct ?

1)100 amps (first 2 largest @100% 2x50)
2)42.5 amps(third largest @ 85%x50)
3)35 amps (fourth largest @70%x 50)
4)360 amps(the remaining 12 welders 12x50=600 x60%)
------
537.5 amps total


could i include the 70% duty cycle multiplier .84 to the calc ?
537.5 x .84 = 451.5

 

[BAHTAH]

16 Welders

16 Welders

IMO all the welders would have the same load current based on Table 630.11(A)
Depending on the type of welder that would be 73amps x .84 or .86 to get the load for one welder. 630.11(B) says the minimum load would be based on the 70% duty cycle load of each welder. So using the 73amps x .84= 61.32 amps per welder.
According to 630.11(B) the first two at 100%= 122.64amps, the third at 85%=52.12amps, the fourth at 70%=42.92amps and the balance of 12 at 60%=441.50amps for a total of 659.18 amps. See the Exception and FPN. The actual load will have alot to do with how all these welders are really going to be used. I used the 73amps you listed if its 50amps then the load will be lower but I think the process is correct. Hope this helps..