Isolated Ground circuits combined with standard circuits in the same conduit

[mikederuby]

We are constructing an elementary school that has circuits from both normal panels and isolated ground panels. We are keeping the home runs seperated to a common junction box. We then are running a common conduit system combining the circuits as they are carried to adjacent classrooms and the drops down into the walls. The specifications for our project are vague at best as to the engineers preference. Now that the installation has started the engineer wants the circuits seperated in different conduits. Is there a standard for the installation of isolated ground circuits?

 

[tom baker]

First of all, an isolated ground circuit is of little use. According to the IEEE, the results range from no effect to worse.
The NEC does not require an isolated ground but allows it.
Perhaps when we had computers that were networked with RG59 or RS232, the ground issues were signficant. Now with CAT 5 type wiring, its just not an issue.
No standard that I know of for IG installations
I would be curious as to why they want an IG circuit?

 

[infinity]

I agree there is no real standard but if the customer is paying for separate conduits then he should get separate conduits. This is a design issue, not a code issue and as Tom pointed out a waste of money.

 

[LarryFine]

Just to mention it, though, there is no electrical problem with both types sharing a raceway. Just treat the insulated EGC as you would any ungrounded conductor, using wirenuts, etc.

 

[iwire]

The specifications for our project are vague at best as to the engineers preference. Now that the installation has started the engineer wants the circuits separated in different conduits.

If it was not clear on the specs IMO it is up to the engineer to provide some sort of evidence that you should have known to keep them separate.

Is there a standard for the installation of isolated ground circuits?

None that I know of and will point out it is very common to run the circuits together.

The manufacturers of modular office partitions run IG circuits and non IG together in common raceways.

I also have seen or worked with a lot of pre-manufactured wiring systems that run the circuits together.

Sometimes when confronted by this type of problem I will point out that every nut, bolt, device, equipment etc has detailed specifications but you (the engineer) did provide any clear specification for this item you feel is so important.

 

[mikederuby]

More Detailed Info

More Detailed Info

The engineer came out to the project and made a report. In the report we were instructed to install piping and conductors in seperate conduits at computer panels.

Specification section 16120, page 3, line 31 thru 34 says we can install up to 6-#12AWG current carrying conductors per conduit. The plans do not indicate seperate conduits for computer runs.

The engineer responded as follows: Specification section 16110-2, lines 26-33, states to install complete, seperate conduit systems for all electrical systems on this project to include, but not limited to the following. New service entrance, electrical power and lighting feeders, electrical power and lighting circuits, control wiring furnished by this contractor, communication systems and other electrical systems. The drawings also indicate seperate home runs for clean and dirty power and is shown seperate in the wire routing on the drawings. Six conductors (3 circuits, 3 neutrals) may be combined in one conduit provided that all are either general purpose power or isolated ground power.

The engineer is hanging his hat on the "other electrical systems" as to mean the isolated ground circuits. We feel that the isolated ground circuits fall under the category of "electrical power and lighting circuits" and not an other electrical system.

The remark that the drawings indicate seperate conduit systems is misleading. The drawings indicate a home run arrow for each and every circuit. The drawings are diagramatic indicating which devices are served by which circuit.

 

[iwire]

Good luck, I can see both sides of this.

I think some moderating will need to be done by the project owner or GC.

IMO the circuits to the PCs are power wiring.

 

[infinity]

Good luck, I can see both sides of this.

I think some moderating will need to be done by the project owner or GC.

IMO the circuits to the PCs are power wiring.

I agree, the engineer is trying to cover his butt because he forgot to add one sentence in the specification stating that IG circuits require separate conduits. Sounds like the owner should pay for the additional work or it should all go in the same conduit.