grounding of conduits

[copper chopper]

There are 7 - 4 inch rigid metal conduits underground for a 2500 amp service with bonding bushings on 1 end of each pipe. can i run a 4/0 ground wire to each of them and end up on the ground bus with it, there is a 5000 kcmil equipment ground in each pipe? there is no way to get a larger size conductor on these bushings. any ideas would be greatly appretiated. also code articles..

 

[don_resqcapt19]

What size are the ungrounded conductors in the conduits? Is this a service or a feeder? I know you said service, but service raceways do not normally have EGCs.

 

[petersonra]

There are 7 - 4 inch rigid metal conduits underground for a 2500 amp service with bonding bushings on 1 end of each pipe. can i run a 4/0 ground wire to each of them and end up on the ground bus with it, there is a 5000 kcmil equipment ground in each pipe? there is no way to get a larger size conductor on these bushings. any ideas would be greatly appretiated. also code articles..

If this is an EGC on a 2500A breaker, 250.122 would require at least a 350. A 4/0 would not cut it.

I am pretty sure a 5000 kcm conductor would cover it though.

Why would you need to bond the RGC anyway? isn't it already bonded at the other end?

 

[kwired]

I am assuming service raceways that likely run from a transformer to the service equipment.

Are these raceways bonded to anything else on either end, like with a locknut through a KO? If they are isolated - I understand what you are doing, you need to bond this raceway, only bond it on one end so the raceway doesn't become a parallel to the neutral. I believe you need to bond with a conductor sized to T250.66. As been mentioned - if not service conductors then it is sized to 250.122.

 

[infinity]

I'm confused, if these are service entrance conductors then why is there an EGC in the raceway? It may be possible to size the bonding jumper for each raceway can be sized according to the ungrounded conductors in each raceway.

 

[texie]

As others have noted, I'm wondering if you are referring to service conductors or a feeder. If these are in fact service conductors in metallic raceways, then you don't have any equipment grounding conductors in the raceways and you would bond the raceways at the service per 250.102 (C)(2). Note that the bonding jumpers in this case only have to be sized to the conductors in each raceway if you use a separate jumper to each raceway. If you choose to use one and loop it through each bonding bushing then it would have to be sized on the total area of the conductors, which in most cases is not practical. You didn't mention the conductor sizes but that is key here.
If we are talking about a feeder, then that is a different story.