Parallel conductors for 600A distribution panel

[NOV]

For a 600A feeder, using the 75 deg C column, wouldn't parallel 300KCMIL be acceptable based on Article 240.4(B)? And would that also hold true for parallel 250KCMIL since at 75 deg C it's good for 510A and the next standard overcurrent device would be 600A? It seems like I always see parallel 350KCMIL specified for 600A, and it looks like it would be a pretty nice cost savings if the smaller conductors are permitted.

 

[d0nut]

You wouldn't have a 600A feeder in either of the cases you mentioned. You would have a 570A feeder or 510A feeder, respectively. You could still protect the conductors with a 600A breaker, but you can't put 600A of load on them. Your feeder is required to be sized according to the load on it, so by using the smaller conductors you would be limiting the load you can put on the panel.

 

[NOV]

Thank you and yes, I should have said 600A overcurrent device, not feeder.

 

[Carultch]

Thank you and yes, I should have said 600A overcurrent device, not feeder.

If the feeder supplies a panelboard where loads can be added, it isn't obvious to a future user to know that they are limited to 510A or 570A. It might be compliant with the load in your plans, but someone in the future might see vacant space on that 600A panelboard as an opportunity to use the full 600A. Or your own crew might have a change of plans of how to distribute circuits, and realize it is more convenient to move a couple circuits to that 600A panel that seemingly has 90A or 30A of extra load capacity.

Opting not to take credit for 240.4(B), mitigates the risk that the feeder gets overloaded by someone who doesn't realize you took credit for that rule. It also helps standardize on the sizing to make all 600A OCPD's have a full 600A of feeder.

 

[infinity]

510 amps with a 600 amp OCPD is code compliant, is it a good design that depends on who's paying the bill.