The plant where I work at had a 1200A 480V 4W 3PH Panel installed. I got involved in shutting down the sub-station so the EC could tie-in the feeders. They ran 4-sets of 350MCM in 3” IMC. They had a 1/0 equipment ground in each conduit, but after checking with the code book it appears it should have been 3/0 according to Table 250-122. Is there some reason the EG was reduced, i.e. because IMC was used or is there some other reason for its reduction? Other then replacing the 1/0 with 3/0, what can be done to remedy this issue? Maybe something like parallel cables in 250-122(F) (2).

Something else that was kind of odd, they installed bonding bushings on all the conduits. But they didn’t run a bonding jumper from the bushings to the ground bar in the panel. Why would you install bonding bushings but not bother with the jumper isn’t that the function of a bonding bushing, to make sure your conduit is electrically bonded to the enclosure? I agree all that was need on IMC are two locknuts one on the outside of the box and one on the inside and then use a plastic bushing. Why go to the expense of bonding bushings and not use them. They also did the same thing at two junction/pull boxes, used bonding bushing at the conduit entries but didn’t bother to put jumpers or bond to the junction boxes.


[This message has been edited by bjwill (edited 07-03-2004).]