Hello:

I am installing a new elevator controller on the top of a 23 story building that requires a dedicated equipment grounding conductor that will be run back to the service equipment location. Running this EGC, with the existing phase conductors is not possible without first removing them. The raceway is a 3 inch Rigid Galvanized Steel Conduit, and appears to be a good grounding path with no corrosion, and all fittings are tight.

I have a spare conduit that runs along this conduit that I would like to use.

This appears to be a code violation per Article 250, but I wonder if the CMP is referring to the service conductors, and not to an equipment ground.

I am aware that the impedance of the system may be higher if I do this.

Is this allowable?

Thanks,

Peter Volpe
Electrical Engineer


[This message has been edited by Joe Tedesco (edited 05-21-2002).]

I haven't seen the 2002 version, but Phillip Simmons' Soares Book on Grounding on the uses and abuses of grounding has been outstanding.

Peter,
You did not say if the service is a separate service or not. Most elevator rooms I've done are so we will assume this one is also.

You can install an equipment ground in it's own conduit. Yup it raises the impedance WAY high in this case but don't forget, it plays almost no role in fault clearing at any rate, it's only there as a 0 point reference.

My big question is WHY do you need one running all the way back down to, I assume, the building grounding electrode from the 23rd floor? Is there no building steel? In lieu of that, is there no grounding electrode in the closets for xfrmr reference?

If elevator equipment is that sensitive, this stuff is doomed anyway, or are the elevator people becoming like computer people, you know "Our stuff is special".

Good luck.

George,
This is an EGC not a grounding electrode conductor and it will carry the fault current. I don't see any exceptions even for an isolated EGC. It is required by 250.134(B) and 300.3(B) to be in the same raceway as the power conductors. If the circuit is above 200 amps or so, the additional inductive reactance of an EGC in a second matallic raceway may very well be high enought so that the OCPD does not open.
Don(resqcapt19)

Don,
OOOOOOPS, I did get that wrong. agreed

If this is an IGC [Isolated Grounding Conductor] I think you could run it separate from the Subfeeder or Branch Circuit's Conduit and comply with the NEC.

The "Gurus Of The NEC" have the answers, whereas I only have suggestions and thoughts.

Scott S.E.T.

Scott,

Doesn't 250.146(D) Say " - - - run with the circuit conductors. - - - ." ?

The basic rule of 250.134(B) is not altered by the word " Isolated " of 250.146(D) which is part of 250.146 Section.