Grounding conductor based on GFP setting for breaker

[coop3339]

We recently had a situation where a tap box in a gear lineup was replaced with a 480V, 4000A breaker. The tap box used to serve as a line side tap and feed outside to a solar disconnect where the neutral and grounds were bonded. Since the system now has a main breaker instead of a tap, the conductors that feed to the existing disconnect outside are no longer considered service entrance conductors, they are now a regular feeder. Also this means that the neutral to ground bond must be removed.

The problem is that the grounding conductors run with the parallel sets are now sized too small. They are 3/O and should be sized at 500KCML for the 4000A breaker. The feeders are also in 4" rigid metal conduit. Also because of the size and voltage, the GFP on the new main breaker is limited to 1200A for 1 sec per 230.95

The install is on 2017 code

The problem is that the original plans called for grounds to be routed with the phase conductors. Otherwise there wouldn't be an issue because the conduit could act as the ground. My thought is that since the NEC 230.95 requires the GFP to be set at 1200A and T250.122 states that a 1200A breaker would need a 3/O ground there is a good case for leaving the size as is. This would have to be under engineering supervision...

Unfortunately, I don't see a path to make this code compliant without removing or upsizing the grounding conductors. Please let me know if I may be missing something...

 

[don_resqcapt19]

At one time the code said you could do that if the ground fault protection device was specifically listed for the protection of the EGC. There was never a device with that listing so the language was removed from the code. You are stuck with having an EGC that is suitable for the 4000 amp OCPD.

 

[coop3339]

At one time the code said you could do that if the ground fault protection device was specifically listed for the protection of the EGC. There was never a device with that listing so the language was removed from the code. You are stuck with having an EGC that is suitable for the 4000 amp OCPD.

Thanks Don. This project has been an ongoing nightmare. At least the mistake is on the engineer but it is going to require a lot of work and a shutdown for us to repair it...

 

[letgomywago]

This is something I don't understand why there isn't any allowance for it since the rigid on its own satisfies the egc for this amd you're allowed to run as many eqc as you want just one of them needs to be large enough for the circuits in the conduit why can't a parallel feeder in a metalic raceway listed as a egc and then have an additional smaller wire type.

 

[texie]

Assuming that the steel conduit is properly done end to end, then yes and as the OP mentioned, one could just remove the original SSBJs and be compliant. If this was on my turf as the AHJ, I would be inclined to allow as it is given the steel raceways and recognizing that removing the original SSBJs is not likely possible without completely repulling the entire set(s) as a practical matter. I just don't see any safety issue by just leaving the ground conductors as is.

 

[don_resqcapt19]

While the code clearly would permit the RMC to be the EGC, the OP says the project specifications require a wire type EGC run with the circuit conductors.

 

[coop3339]

Thank you for your responses. Because this is an addition to an existing system, the engineer of record agreed to add a note to clarify that the GRC shall be the EGC and the existing 3/O will remain as a redundant grounding conductor.

 

[texie]

Thank you for your responses. Because this is an addition to an existing system, the engineer of record agreed to add a note to clarify that the GRC shall be the EGC and the existing 3/O will remain as a redundant grounding conductor.

As I said in my previous repsonse, I think this is a good solution. But you better verify that the AHJ will go along with it as it technically does not meet code.

 

[wwhitney]

As I said in my previous response, I think this is a good solution. But you better verify that the AHJ will go along with it as it technically does not meet code.

Only if you try to call the redundant conductor an EGC, which calling it a grounding conductor comes very close to. Better to just call it a redundant conductor, safed off by bonding at both ends, and remove any green markings.

Cheers, Wayne