GEC in metallic conduit

[Clark Mason]

I am working for an engineer who wants me to install a GEC to the building's underground metal water pipe in rigid metallic conduit. I know I can do this if I install bonding bushings on each end.

My question is should I do this. It's my understanding that the GEC will be a more effective conductor in a lightening event if the GEC is not in a ferrous conduit.

Any thoughts and/or research reports I can take to him might help.

 

[peter d]

Re: GEC in metallic conduit

While I don't do much work where this situation is encountered, I would say that PVC is a far more preferable approach. The few installations I have worked on or reviewed plans for called for PVC. You will experience a big labor and material savings by using PVC.

Is there some particular reason, such as physical damage, why RMC is being specified?

 

[Clark Mason]

Re: GEC in metallic conduit

Peter,
Thanks for the thoughts. The EE is stuck in some specs written 50 years ago I guess. I am trying to convince him it would be a better performing system if he let me run the GEC exposed (there are no physical damage issues) or at in PVC. The whole GEC is only about 40' long so cost is not a huge concern.

 

[peter d]

Re: GEC in metallic conduit

You're welcome.

There is a thread, now buried deep in the forum, where this very topic [The "choke effect" of metallic conduit on a GEC during a transient event] was debated. I don't remember the concensus, but there were arguments on both sides.

If damage is not an issue I see no problem with running the GEC exposed. This is very frequently done, at least in most residential situations.

[ March 30, 2005, 01:17 PM: Message edited by: peter d ]

 

[wirenut1980]

Re: GEC in metallic conduit

Mr Mason, just out of curiosity, why do you think the GEC will be a more effective conductor in a lightning event if it is not in a ferrous conduit?

 

[Clark Mason]

Re: GEC in metallic conduit

Peter, I found the thread this morning before I made the original post.

It gave a decent explanation but I was looking for something more "expert" to take to this guy.

 

[Clark Mason]

Re: GEC in metallic conduit

Originally posted by wirenut1980:
Mr Mason, just out of curiosity, why do you think the GEC will be a more effective conductor in a lightning event if it is not in a ferrous conduit?

I did a little research before hand on the "choke" effect.

 

[roger]

Re: GEC in metallic conduit

Clark, when the conduit is bonded to the GEC at both ends, there will not be a choke effect, the conduit and wire simply becomes one conductor.


Roger

[ March 30, 2005, 03:12 PM: Message edited by: roger ]

 

[wirenut1980]

Re: GEC in metallic conduit

After a little reading on some great threads found here and Here , I agree with Roger in that if the GEC is bonded to the conduit at both ends, then there will be no choke effect. I could not locate any books or other publications online.