Using the conduit as the ground.

[rogerpopa]

We have two conduits running parallel to a distribution board to create 400 amps. They are two 2" EMT with 4 4/0 cables each. We are running 1 additional conduit with the same cables to the same switch board to create 600 amps. The existing conduits are being used as the ground. Can we do the same with the new conduit, and where can I find this in the code book?

[renosteinke]

No you can't. Ground must be sized for the amount of fault current available. While a run of pipe will carry enough to trip a 20A breaker, it won't be reliable for 600A.

[tom baker]

Originally posted by renosteinke:
No you can't. Ground must be sized for the amount of fault current available. While a run of pipe will carry enough to trip a 20A breaker, it won't be reliable for 600A. Can you cite a code rule that prevents use of the raceway as an equipment grounding conductor?

[dereckbc]

Roger, you can do this. You will find it in 250.118. However I would suggest also running an EGC.

[ April 01, 2003, 07:01 PM: Message edited by: dereckbc ]

[tom baker]

Derek, you are correct. Its important we note the NEC is a minimum standard and the poster was asking if he could use the raceway as an equipment grounding conductor.
Later I'll look at the GEMI software program from the Steel Tube Institute and it will calculate the required size, but its not a code requirement to use an equipment grounding conductor.

[dereckbc]

Tom, I know it is not required. Just a professional suggestion. :)