leboot
Member
- Location
- Baltimore, MD United States
- Occupation
- Electrical Engineer
I'm working on a commercial project in an industrial complex.
Existing there are :
-two sets of 3/C #350 + #3GW (CVTC multiconductor cable) currently serving an existing piece of equipment (motor) that has been removed.
-Cable is routed in tray from gear and then transitions to rigid metal.
-a 800A feeder breaker that was set to 600A to serve demolished equipment
- system is 480V,3PH,3W
The owner would like to re-use these cables to feed a new distribution panel in the same place as the removed equipment. They initially wanted an 800A panel, but the cables aren't large enough to allow for that. Based on the #3 GW, my thought is that we could only have a 300A panel using one set of cables. The cable is rated for 310A and we only have a #3 GW. Using two sets of cable would require a larger GW bc of 250.122(B) where the undergrounded conductors are increased from minimum size, the EGC shall be increased proportionally.
The owner came back and said they want to use all the cables and set the breaker for 400A and implied that there are different interpretations of the NEC on this.
My question is: am I missing something? Is there something in the code that allows for smaller equipment grounding conductors? In looking at the previous installation with the 600A CB and #3GW, I think the #3GW is too small.
Maybe they were using tray and conduit as the EGC before?
Any thoughts would be helpful.
Existing there are :
-two sets of 3/C #350 + #3GW (CVTC multiconductor cable) currently serving an existing piece of equipment (motor) that has been removed.
-Cable is routed in tray from gear and then transitions to rigid metal.
-a 800A feeder breaker that was set to 600A to serve demolished equipment
- system is 480V,3PH,3W
The owner would like to re-use these cables to feed a new distribution panel in the same place as the removed equipment. They initially wanted an 800A panel, but the cables aren't large enough to allow for that. Based on the #3 GW, my thought is that we could only have a 300A panel using one set of cables. The cable is rated for 310A and we only have a #3 GW. Using two sets of cable would require a larger GW bc of 250.122(B) where the undergrounded conductors are increased from minimum size, the EGC shall be increased proportionally.
The owner came back and said they want to use all the cables and set the breaker for 400A and implied that there are different interpretations of the NEC on this.
My question is: am I missing something? Is there something in the code that allows for smaller equipment grounding conductors? In looking at the previous installation with the 600A CB and #3GW, I think the #3GW is too small.
Maybe they were using tray and conduit as the EGC before?
Any thoughts would be helpful.