Parallel ?

[Ed Carr]

I have two 4" rigid conduits each containing six
500mcm cu conductors. They are feeding a 3 phase
panel with a neutral. My inspector is telling me
that it may not pass. In conduit #1 I have phase A and phase B.
In conduit #2 phase C and the grounded conductor.
I have been going through my book and can't find anything
that says this is a violation. This is the service entrance
from utility transformer. Anyone?

Thanks, Ed

 

[Dennis Alwon]

Are you reading 310.4(C)-- off the top of my little head I say it's a violation. Well it seems that doesn't help-- sorry.

 

[jumper]

Each conduit should contain a conductor of each phase and a neutral.
What is your grounding method?

 

[Dennis Alwon]

Sorry Try article 300.3(B)

 

[augie47]

agree. afraid it's a violation. see 300.3(B)

 

[Ed Carr]

Grounding is at the pad mount transformer.
Earth ground at the panel is 4/0 cu to a ground
rod and the steel building.

Ed

 

[jumper]

Grounding is at the pad mount transformer.
Earth ground at the panel is 4/0 cu to a ground
rod and the steel building.

Ed

So these are sevice entrance conductors and the panel is the first means of disconnect?

4/0 cu to a ground rod?

 

[Ed Carr]

Jumper, yes.

 

[Ed Carr]

Dennis & Augie, what about 250.122 F?

Ed

 

[Dennis Alwon]

Dennis & Augie, what about 250.122 F?

Ed

This means that you need an egc in each conduit. Figure the size needed based on 250.122 then put that size egc in each conduit.

 

[iwire]

Dennis & Augie, what about 250.122 F?

Ed

That applies only to the EGC which if this is a service you will not have.

Unless you can fit into the exception to 300.3(B) that allows isolated phase installations the inspector is correct. You will have to have each phase in each conduit.

 

[Dennis Alwon]

4/0 cu to a ground rod?

This is sometimes speced by the engineers.

 

[jumper]

This is sometimes speced by the engineers.

This I know big time! Engineer up here does overkill all the time.
I assumed it was the OP's call.

 

[Ed Carr]

I think 392.8 D has got me dead in the water.
Could I add 1 grounded conductor to conduit #1?

Ed

 

[Ed Carr]

Iwire, I missed egc. You are correct.

Thanks, Ed

 

[roger]

Besides the already mentioned article sections, we can just apply theory and think about inductive heating. Depending on how the loads are distributed at any period in time, there is a possibility that you could have non canceling current flowing because of the separation in separate metallic raceways which would result in heating of these raceways and conductors.


Roger

 

[roger]

I think 392.8 D has got me dead in the water.
Could I add 1 grounded conductor to conduit #1?

Ed

No, there would still be a possibilty of non-cancelling current flowing in both raceways.

Why would article 392 come into play?

Roger

 

[Ed Carr]

Roger I read 392.8 D as saying I would need 3 conduits
or am I wrong?

Ed

 

[Dennis Alwon]

Roger I read 392.8 D as saying I would need 3 conduits
or am I wrong?

Ed

Ed, 392 is for cable tray. I thought you had conduits run

 

[Ed Carr]

I need new glasses Dennis, thanks.

Ed