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#179106 06/26/08 06:22 AM
Joined: Jul 2007
Posts: 265
I just finished the slab work on a metal building. Building will have a 600a service, 600a distribution panel, and several smaller panels through out. Now the question, the drawing specified a 3/0 copper wire to bond the plumbing, is this the norm or is it a little large for its use? Just wondering.


Life is tough, Life is tougher when you are stupid
Joined: Oct 2002
Posts: 482
I don't see any reason to deviate from the drawing twister, unless the drawing violates code. If the engineer has determined that 3/0 copper is required to clear the worst-case short, then I would not argue with him. Deviating from the engineer's specs can only lead to trouble for you.

Good Luck!

Zapped #179109 06/26/08 10:33 AM
Joined: Mar 2005
Posts: 399
Seems a little larger than normal. What size service entrance conductors ? Section 250.66 would list the required GEC. What the Eng. specified is what you need to build, unless he allows a change order.
What is built can always exceed Code.

If it was easy, anyone could do it.
Joined: Mar 2005
Posts: 1,213
What service conductors did he spec out? 3/0 is the right size for 1500kcmil USE (625A ampacity) or similar. If multiple smaller cables are used, 2/0 may be acceptable, but you'd end up having to derate for # of conductors in a raceway, which would put you right back at 3/0. Seems like a reasonable requirement to me.

You could always call the engineer and ask.

Joined: Jan 2005
Posts: 5,370
Likes: 1
Cat Servant
It's a situation like this that highlights some of the confusion the code has in it, especially in Article 250.

After all, just what are we attempting to accomplish with that wire? The ground rod / ufer / whatever only requires a #6, regardless of the service size.

Clearing faults? Is there ANY possible circumstance where the plumbing could possibly be exposed to the full service fault current? Does it ever make sense to require more copper in the wire than there is in the pipe itself?

I think we're wrestling a dinosaur here .... the water line once was the grounding electrode, yet today we're -at most - using it as a supplementary electrode. More realistically, we are bonding the pipe, to protect against it being accidentally energized.

Still, no harm done .... and until the code panels get their acts together (maybe even get an grammar expert involved), engineers will be stuck specifying idiocy.

Joined: Jul 2004
Posts: 9,788
Likes: 14
I agree with John, the 250.66 requirement for connection to water pipe is a remnant of the days when water supply lines were metal and that was your best ground electrode. Now days the plumbing lateral into a building will generally be PVC and the only real grounding will happen with the inadvertent connection to building steel via the pipe supports.

Greg Fretwell
Joined: Jan 2005
Posts: 316
Yes it does seem to be large.
But keep in mind the nEC is a minimum

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