3000 Amp Service Ground

[dduffee260]

We have a 3000 amp 208/120 volt service. It starts at the POCO's pad mount transformer then to an outdoor CT enclosure. From there it goes under a slab to a 3000 amp MCB switchboard. It has 8 sets of 4-500 kcmil feeders. We use Table 250.66 which says to use a 1/0 for each service feeder.

Since the CT enclosure is before the MCB, are we required to pull 8-1/0's back to the CT enclosue? Also on the equipment ground do we attach 1-400kcmil to the structure?

There is a table on the plans that tell us the ground is a 400 kcmil. I can't see where we are required to pull a 400 kcmil ground with each feeder service coming in. Also I can't see where we could attach 8-1/0's to the CT enclosure.

The POCO here does not supply the ground, they ground only their equipment with ground rods. So from the transformer to the CT there will be no grounds in the feeders.

 

[iwire]

You keep saying 'feeders' which is confusing as it sounds like the service disconect is at the MCB.

It sounds to me like you have service conductors from the transformer, to the CT and then onto the MCB.

If that is the case you will not pull any GECs or EGCs in with the service conductors.

The CT cabinet will be bonded to the grounded conductor (neutral).

 

[infinity]

I agree with Bob. A feeder wouldn't begin until after the service disconnect. Before that, all bonding is done with the grounded conductor. An EGC pulled in with the service conductors would create a parallel path for the neutral current which is prohibited.