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Welder Sub Panel

2K views 8 replies 2 participants last post by  NolaTigaBait 
#1 ·
Im adding a subpanel that will feed 3 arc welders. A little confused on 630.12b...it says I can have ocp at 200% of the conductor ampacity. Total for 3 welders is 79 amps...so im thinking #4 copper on a 150 amp breaker...It doesnt sound right...it would seem that if I want to use a 150 amp breaker for a sub-panel , I would have to use 1/0 copper or am I good using #4??
 
#3 ·
625.11 determines the conductor size

625.12 determines the overcurrent size.

Without knowing the welder info all we can say is maybe.

How did you come up with 79 amps?
First one is 36 amps @ 60% duty cycle...the second and third are 60 amps @ 30% cycle...
480*36*.78= 13478
480*60*.55=15840
480*60*.55=15840

Ok 100% of first 2= 31680
85% of 3rd=11685

First 2 are 1phase so 31680/480=66
3rd is 3 phase so 13748/830=17

So base my feeder off of 83 amps...
#4 copper good for 85 amps...ocp at 175 technically...
I figured 150 is a good round number:jester:
 
#4 ·
I feel like my numbers are right...just not sure if that 200% would apply to a panelboard...Kinda seems wrong...Ive used the 200% for a feeder ocp going to a "6 pack" of welders...but that came with a factory installed trough with ocp for each welder built in...
 
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