Sharing a Conduit?

[Sparks4All]

We are doing a tenant improvement in a large building. The contractor that wired the shell ran (3)3" conduits into the space. We are installing an 800 Amp MDP in the retail space with 3 parallel runs in the 3 conduits. We will need a grounding conductor for the transformers and an isolated ground in a addition to the EGC's. There is not structural steel. The entire structure is concrete. There is no way to add a new conduit back to the GES. I don't believe we can run the grounding conductors inside one of the conduits of the parallel runs. Is this the case?

 

[petersonra]

I don't believe we can run the grounding conductors inside one of the conduits of the parallel runs. Is this the case?

What provision of the code would prohibit this? are these metal conduits? If so maybe if they ran a green wire in them you could just repurpose those wires if sized correctly.

 

[Sparks4All]

What provision of the code would prohibit this? are these metal conduits? If so maybe if they ran a green wire in them you could just repurpose those wires if sized correctly.

Yes, the conduits are EMT. Each Parallel run will have a 1/0 equipment grounding conductor. We need a 3/0 ground to a ground plate for the transformers ran back to the buildings electrode system.

 

[Dennis Alwon]

I believe you are talking about the grounding electrode conductor. This conductor can be run inside the conduit, AFAIK, but it cannot be solid. Obviously at 3/0 it won't be.

 

[iwire]

You could run the IGs with the feeder without much issue.

The GEC could be a PITA due to bonding requirements

But regardless keep in mind the amount of conductors in each raceway must be the same so you would be running three IGs and three GECs.

310.10(H)(3) Separate Cables or Raceways. Where run in separate
cables or raceways, the cables or raceways with conductors
shall have the same number of conductors and shall have
the same electrical characteristics. Conductors of one
phase, polarity, neutral, grounded circuit conductor, or
equipment grounding conductor shall not be required to
have the same physical characteristics as those of another
phase, polarity, neutral, grounded circuit conductor, or
equipment grounding conductor.

 

[GoldDigger]

I believe you are talking about the grounding electrode conductor. This conductor can be run inside the conduit, AFAIK, but it cannot be solid. Obviously at 3/0 it won't be.

But will the AHJ consider that putting the GEC into only one conduit breaks the parallelism of the three sets of circuit conductors?
The GEC is not itself a circuit conductor, but the fill ratio of one conduit will be different from the other two.

 

[infinity]

It's a technical violation as Digger has outlined but electrically it probably won't make any difference. If you need the GEC in a separate conduit and cannot run another you might have to somehow if possible reconfigure you feeder in two of the 3" EMT's and use the third one for the GEC.

 

[Sparks4All]

It's a technical violation as Digger has outlined but electrically it probably won't make any difference. If you need the GEC in a separate conduit and cannot run another you might have to somehow if possible reconfigure you feeder in two of the 3" EMT's and use the third one for the GEC.

We are looking at running 4 parallel runs in two of the conduits. The issue is the breakers on both ends are Square D I-line breakers with triple lugs on each phase. We are having the supplier see if we can get 4 lug terminals for each phase. The current lugs only accept 1 conductor, up to 500 MCm for each of the 3 lugs.

 

[infinity]

We are looking at running 4 parallel runs in two of the conduits. The issue is the breakers on both ends are Square D I-line breakers with triple lugs on each phase. We are having the supplier see if we can get 4 lug terminals for each phase. The current lugs only accept 1 conductor, up to 500 MCm for each of the 3 lugs.

Depending on the manufacturer there are typically several different configurations when you get into the 800 amp category. Maybe you'll get lucky.

 

[petersonra]

By any chance does the underground EMT qualify as a grounding electrode?