240.100. 250.187. 250.122 and 250.102(C) (1)

[Dale001289]

Article NEC 240.100 allows feeder protection ‘whendesigned under engineering supervision’. Does this allow Tables250.102(C )(1) and 250.122 to be circumvented for equipment bonding conductors? This is a 13.8kV system and there's a LRG at 400A connected to the bus.

 

[mayanees]

over 1000 VOlts

over 1000 VOlts

Article NEC 240.100 allows feeder protection ‘whendesigned under engineering supervision’. Does this allow Tables250.102(C )(1) and 250.122 to be circumvented for equipment bonding conductors? This is a 13.8kV system and there's a LRG at 400A connected to the bus.

That's not my interpretation. I use that for protection of the ungrounded conductors over 1000 Volts, where ampacity protection can be 3X for fuses and 6X for breakers and electronic trip fuses. It's usually rationalized because the connected load on the MV feeder could never exceed the ampacity of the cable, and it becomes necessary to provide coordination of protective devices. I would also plot out a TCC for something not protected at ampacity, that shows a cable withstand line that's protected against short-circuit damage by the 3-6X setting.

 

[Dale001289]

That's not my interpretation. I use that for protection of the ungrounded conductors over 1000 Volts, where ampacity protection can be 3X for fuses and 6X for breakers and electronic trip fuses. It's usually rationalized because the connected load on the MV feeder could never exceed the ampacity of the cable, and it becomes necessary to provide coordination of protective devices. I would also plot out a TCC for something not protected at ampacity, that shows a cable withstand line that's protected against short-circuit damage by the 3-6X setting.

Thanks, I've spoken to a couple colleagues who basically say the same thing.