EGC: Conduit vs. Wire

[mhernandez]

Is there a Rule-of-Thumb when deciding to use conduit or wire for an egc?

 

[charlie b]

I never use conduit alone. But that is a design choice, rather than a code requirement.

I may be wrong, or at least out of date, on this statement, but I seem to recall that the city of Chicago specifically requires a separate ground wire. Welcome to the forum.

 

[mhernandez]

Thanks.

Well I'm asking because the project is an existing grounding system assessment. In all our new projects, we specify egc wire to be installed with feeders. If client wants to remain using the conduit as egc, they need to do testing on it, correct?

 

[iwire]

There is no NEC required testing.

 

[iwire]

I seem to recall that the city of Chicago specifically requires a separate ground wire.

They require tubing or conduit but not the wire EGC.

 

[mhernandez]

Although the conduits being used as egc are code compliant, I can't assure in my assessment that the conduit is installed in a correct way that it will provide a low-impedance path with only visual inspection and no testing.

 

[petersonra]

Thanks.

Well I'm asking because the project is an existing grounding system assessment. In all our new projects, we specify egc wire to be installed with feeders. If client wants to remain using the conduit as egc, they need to do testing on it, correct?

Just how would you test it?

My biggest complaint with using the conduit as an EGC is that some very dubious things are done at the ends of the conduits on occasion that make me wonder.

I can't tell you how many times I have seen the set screwed or the dimpled type EMT fittings come loose, especially where subject to vibration. The compression style seem to be a better choice. You still have to worry about whether the guy put the locknut in the right way, or bothered to tighten it up.

I also question whether all the metal parts get bonded correctly if there is no wire. A lot of times there are painted sub panels and it does not appear anyone went to the trouble to make sure the panel is properly bonded to the cabinet.

But, if done correctly, metal conduit is at least as good, and maybe a better EGC than running a separate wire.

 

[mhernandez]

Thank you all for your quick replies. We are being paid for a visual assessment where we can list code deficiencies. We don't do testings so I'm just going to let them know that they can use conduit as egc but that's as far as we can go. If they need a performance assessment, they'll need to do some testing for low-impedance path and continuity bonding. Thank you all again.

 

[LarryFine]

Although the conduits being used as egc are code compliant, I can't assure in my assessment that the conduit is installed in a correct way that it will provide a low-impedance path with only visual inspection and no testing.

The same can certainly be said about a conductor-based EGC system.

 

[mcclary's electrical]

The same can certainly be said about a conductor-based EGC system.

I agree, and bad wirenut joint on a wire is just as like ly to come loosed under vibration than a setscrew.

A properly sized, properly installed pipe EGC, will IMO be a better fault current path than the same comparable wire EGC.

 

[jumper]

The same can certainly be said about a conductor-based EGC system.

I agree, and bad wirenut joint on a wire is just as like ly to come loosed under vibration than a setscrew.

A properly sized, properly installed pipe EGC, will IMO be a better fault current path than the same comparable wire EGC.

I am with my fellow Virginians. I used to think differently, before I joined this forum, but I now agree. Conduit or tubing EGCs are just fine.

 

[erickench]

I would think that a ground wire comes in handy if the conduit breaks. You would have a continuous fault current path back to the service.

 

[iwire]

I would think that a ground wire comes in handy if the conduit breaks. You would have a continuous fault current path back to the service.

In a NM job do you run a second wire EGC in case a splice opens in the first EGC?

In a PVC job do you run a second wire EGC in case a splice opens in the first EGC?


In my experience the conductor most likely to be poorly spiced, or not spliced at all is the EGC.

 

[petersonra]

I have had a fair number of issues on machines with wire nuts vibrating loose. Its only happened a few times but they always seem to be buried somewhere non-obvious and a machine can be down for a relatively long time waiting for someone to find it.

If a light or a receptacle stops working in my house due to a loose wire nut it is no big deal. If a 5 cent wire nut comes loose and shuts down a car plant for a couple of hours, its a huge deal.

 

[resistance]

In my experience the conductor most likely to be poorly spiced, or not spliced at all is the EGC.

I agree! I see EGC un-spliced too often.

 

[mhernandez]

So can we agree that for existing conditions, were conduit is used as EGC, is not worth it to pull the existing feeders out just to add a wire EGC? If installation is correctly done, conduit EGC is fine.

But for new projects, Am I over-designing it by bonding the conduits and providing a wire EGC with all feeders and branch circuits?

 

[jumper]

So can we agree that for existing conditions, were conduit is used as EGC, is not worth it to pull the existing feeders out just to add a wire EGC? If installation is correctly done, conduit EGC is fine.?

IMHO, yes

But for new projects, Am I over-designing it by bonding the conduits and providing a wire EGC with all feeders and branch circuits?

See post #2, it is a design issue, unless it is a health care facility and needs redundant grounds. You draw it up and we install it.

 

[LarryFine]

So can we agree that for existing conditions, were conduit is used as EGC, is not worth it to pull the existing feeders out just to add a wire EGC?

Definitely not worth it, unless the customer wants to pay for it to be done. I wouldn't.

I don't know if it's Kosher, but you could always to a load-test on EGC's for important circuits, measuring voltage rise.

 

[kbsparky]

On jobs that have steel structures, we will install metal conduit systems w/o any additional EGCs. The conduit is firmly fastened to the building steel with every strap, box, etc. A loose fitting won't make much difference in the event of a ground fault condition.

OTOH, if the conduits are installed in wood framing, or in other less conductive structures, then we will install a supplemental EGC, and bond it to every box to maintain a good grounding continuity.

 

[e57]

On jobs that have steel structures, we will install metal conduit systems w/o any additional EGCs. The conduit is firmly fastened to the building steel with every strap, box, etc. A loose fitting won't make much difference in the event of a ground fault condition.

Effectively grounded to mounting means is not an effective fault path per se - but does help - in most cases - hurt if isolated and energized. Someday ask me about the dishwashers who went on strike due to multiple faults at various equipment and WALLS..... Boy ....was that a fun job!