conduit as equipment grounding conductor

[millivolt]

I am installing a sub pnl 120/208 3ph 200 amp.
I'm using a discontinued circuit which consists of four 300mcm, three hots and a neutral, I want to use this circuit to feed my panel.
Can I use the conduit (3" rigid aluminum) as the equipment ground or do I have to pull in a 5th wire.
Thanks in advance
Millivolt

 

[celtic]

According to 250.118 you can.

How long is the conduit run?

 

[mdshunk]

Not to derail this very worthy post, but it begs a question for me. I've never worked with aluminium RMC. Do you treat the threads with something like Penetrox before you make up the threaded connection when you're using the pipe as the equpiment bond?

 

[celtic]

I can't cite any code/instruction on this - but we always Penetrox AL connections..pipe or wire.

 

[kingpb]

Correctly stating voltages is very important. The voltage you are working with is probably 208Y/120V. Please refer to IEEE C84.1. Also the proper reference to cable size is KCMIL. The usage of MCM went by the wayside a few years back.

 

[millivolt]

equipment ground

equipment ground

The run is about 150' and noalox was used on all threads.

 

[Rockyd]

The code section that covers this is 300.6 Protection Against corrosion and deterioration. It is a round about combination of (A) ferrous metal equipment, and (B) non-ferrous metal equipment. It soesn't say directly for the non-ferrous, but common sense shold take you there.

250.122 says see250.118 IMC is recognized as a method of grounding.

Because it is aluminum underground, and not knowing the soil condition, I would pull a ground, but doesn't appear to be specifically called out in the code that you would be required to.

 

[hillbilly]

Assuming that all of the joints were made up tight, it sounds good to me.
steve

 

[hillbilly]

"Because it is aluminum underground, and not knowing the soil condition, I would pull a ground"

Who said anything about underground?
I didn't see it.
steve

 

[Rockyd]

Underground?

Sorry, I wasn't through my first cup of coffee.

Steve is right, joints tight, money to be made...let's go (assuming everything else is good to go) !

Pass the Poly-water please.

 

[iwire]

250.122 says see250.118 IMC is recognized as a method of grounding.

A small point here, there is no such thing as aluminum IMC.

IMC is always steel.

RMC comes in Steel, aluminum and even stainless steel.

 

[yanici]

I don't see the word "underground" in Millivolt's post.

 

[DaveTap]

Code allows conduit as ECG, but I'd tighten the nuts and add ground-bushings and wire at each end especially if you're going to be using AFCI or GFCI from that panel. (a ground fault will have to travel all the way to the main panel to sense) I figure if NEC doesn't allow just the electrical nuts at the service why would I allow it for a sub panel? That being said I find conduit to be pretty reliable ECG as long as all the fittings and nuts are tight.

 

[Rockyd]

I concede to hiding behind 250.118(2) instead of 250.18 (3)...point noted.

 

[don_resqcapt19]

Dave,

but I'd tighten the nuts and add ground-bushings and wire at each end especially if you're going to be using AFCI or GFCI from that panel. (a ground fault will have to travel all the way to the main panel to sense)

It would be almost impossible to have a metallic conduit that could not handle the current required to trip those devices under ground fault conditions. The maximum current required is 50 mA. The problem comes in where you are using standard OCPDs to clear a ground fault. The fault return path must be able to carry enough current to cause the circuit to open quickly...that would be at least 10 times the rating of the breaker to get into the instantanous trip part of the time current trip curve.
Don

 

[W6SJK]

Small point - NEC REQUIRES metallic conduit to serve as ground. The ground wire is supplementary.

 

[hardworkingstiff]

Also the proper reference to cable size is KCMIL. The usage of MCM went by the wayside a few years back.

Man, old habits are hard to break. I still use MCM.

 

[e57]

The usage of MCM went by the wayside a few years back.

So did the metric system! Didn't it?

 

[iwire]

Small point - NEC REQUIRES metallic conduit to serve as ground. The ground wire is supplementary.

I disagree, could you elaborate?

 

[petersonra]

I disagree, could you elaborate?

I think what he meant was that if you use metallic conduit it is an EGC and has to be bonded so it is an EGC.