What size Equipment Grounding Conductor would be installed with the tap conductors to a 200a switch. The feeder overcurrent protection is 600 a and the tap conductors run 25 feet and are 3/0 copper and terminate in a 200 ampere switch with 200 a fuses installed.

The EGCs run with the tap conductors will need to be 1/0 copper. You must base the EGC on the overcurrent device it would have be able to open. In this case that would be the 600 amp feeder.

Once you leave the 200 amp switch the EGC may be 6 awg copper.

I agree with you iwire, but it's not thst clear in the NEC. It's one of those things left silent and you need to use logic to figure it out, like you put it, what overcurrent device will it be opening.

As usual the handbook does a better job of explaining things. This is commentary from 250.122
"Equipment grounding conductors on the load side of the service disconnecting means and overcurrent devices are sized based on the size of the feeder or branch circuit overcurrent devices ahead of them."

When in doubt, check out 250.4(A)(5).

In table 250.122 the heading states "Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment, conduit, etc. Sometimes it takes careful reading to get the intent.

[This message has been edited by electricman2 (edited 09-09-2004).]

electricman2 That is exactly what I would have pointed to.

Bob

Bob, where did the 1/0 come from? Table 250.66? or 250.122?

Table 250.122 and it is worth mentioning that the EGCs never have to be larger than the associated circuit conductors. 250.122(A)

[This message has been edited by iwire (edited 09-09-2004).]

Bob,

In that case, wouldn't #1 CU be sufficient for a 600 amp OCPD by table 250.122?

Just trying to figure this out as I rarely work on stuff that large.

Peter

Pete is right Bob, it should be a #1 not a 1/0. You probably let your eyes drift when you were reading the table. common mistake is o size it to the 200a overcurrent device and this would be a mistake.