pulling grounding conductors

[crossman]

One consideration concerning using EMT (or other metallic wiring methods ) as the EGC is the construction of the building itself. If it is all metal structure with metal columns and bar joists, and the conduit is strapped/tie wired to the metal, with multiple conduits from the panels, we end up with a bunch of parallel paths for ground fault current, which is a good thing. The overall impedance of multiple ground fault paths will be lower than a single path.

Throw in the building steel itself bonded at the service, also possble metallic water piping /sprinkler piping/other piping attached to the building structure and/or bonded, the whole thing makes up multiple paths for ground fault current. In this case, a loose EMT coupling screw or corroded fitting will make no difference because of all the other paths available.

Now, with a wood structure, the single EMT path becomes critical for a good ground fault path.

 

[chris kennedy]

I find this to be one of those issues that electricians do just so they can say they are better then those that don't.

Ouch!!! I'll never be better than you Bob. Your a living legend!:grin:

 

[crossman]

I would still run a ground wire, even if that's the case.

There was an article in a past EC&M about a maintenance electrician who was killed when he contacted a piece of EMT that had become disconnected as in the photo. The difference was that it was an all wood structure. In the attic, there was a circuit in EMT that fed a sign on the outside of the building. The EMT pulled loose, leaving the sign without a bond. In the sign, the hot wire faulted to the metal frame. Because there was no bond, the sign frame was energized, and with it, the EMT. The electrician was in the attic, and he made contact from that EMT to another piece of EMT from a different circuit.

While the loose fitting in the photo is certainly not a good thing, depending on the strapping of the conduit downstream, and its attachment to the metal structure, we may still have a good fault path. Of course, this fact does not mean we should be careless when making up fittings. Workmanship is key.

As for the photo. I contend that if the fitting was installed properly, and if the EMT was properly strapped, then it shouldn't have come loose.

 

[infinity]

I have found that the guys who like to always run an EGC in EMT are the ones who don't really need to because their conduit is usually installed properly. It's the ones who slop the stuff in with no supports and exceptionally poor workmanship that should be using EGC's and usually don't.

 

[iwire]

I have found that the guys who like to always run an EGC in EMT are the ones who don't really need to because their conduit is usually installed properly. It's the ones who slop the stuff in with no supports and exceptionally poor workmanship that should be using EGC's and usually don't.

Now that is probably very true. :smile:

 

[iwire]

Ouch!!! I'll never be better than you Bob.

I am not better then anyone.

I just will never say that I always pull an EGC as I don't, and when I don't I do not feel that I am short changing the customer.

If it was a PVC job do people pull two EGCs just in case a wire nut comes off on one EGC?

 

[iwire]

Now, with a wood structure, the single EMT path becomes critical for a good ground fault path.

I agree.

Now can you explain why this is such a bigger concern then a wood structure wired with NM?

A single failed splice in the EGC can do as much as one pulled apart coupling and no one seems to be concerned with that at all.

 

[480sparky]

I have found that the guys who like to always run an EGC in EMT are the ones who don't really need to because their conduit is usually installed properly. It's the ones who slop the stuff in with no supports and exceptionally poor workmanship that should be using EGC's and usually don't.

I find that to be generally true, but I myself have installed devices into boxes and only then noticed I missed a locknut.

Wanting to be good does not mean perfection. :smile:

 

[crossman]

Now can you explain why this is such a bigger concern then a wood structure wired with NM?

Well, I never said it was a bigger concern! They are both equally critical.

I suppose there may exist a perception, when comparing wiring connections to EMT fittings, that EMT fittings and set screws have a higher rate of improper installation or subsequent continuity failure due to corrosion or excess movement which compromises the electrical integrity of the fault path. I cannot say that the perception does not have some validity.

 

[George Stolz]

I'll admit it, there have been a few times I've gone back through pulling conductors in EMT I've installed, to find an untightened set screw in a connector at the box. I try really hard, and make a conscious effort to do a good job, but on occasion I screw up.

I usually pull in a conductor; belt and suspenders can't hurt.

However, just the other day I ran out of green on something I was working on, and was confident that I hadn't left a screw loose, so I used the EMT as the EGC. It was a short run, and one that I could quickly verify everything was tight once I realized I was short. Dragging a big roll of #12 over to my 50' run just seemed like a waste of time to me at that point, I needed to get on to the next task.

 

[chris kennedy]

I find this to be one of those issues that electricians do just so they can say they are better then those that don't.

Your right Bob. I spend the extra money and do the extra work just so I can say I'm better than some one else. Has nothing to do with your saftey, mine or the next guy's!

 

[augie47]

it's there, but it ain't right ?

it's there, but it ain't right ?

I think one of the interesting delimas is when you find a job with a metallic conduit and a EGC but the EGC is smaller than the Code requires.
The job would be fine (as in Code compliant) if there was no EGC.
Now what should the inspector do ??
Reject it and have the electrician remove the undersized GEC and rely soley on the conduit system ??

 

[infinity]

I think one of the interesting delimas is when you find a job with a metallic conduit and a EGC but the EGC is smaller than the Code requires.
The job would be fine (as in Code compliant) if there was no EGC.
Now what should the inspector do ??
Reject it and have the electrician remove the undersized GEC and rely sole on the conduit system ??

As an inspector you enforce the code as written. The guy has the option to re-pull, or pull out the undersized EGC. It's not really the inspector's call.

 

[augie47]

I agree, and that is what I do, but, when the elect to just pull the EGC out I can't help but wonder if I lowered the safety level of the job..

 

[nakulak]

If you guys will get the utility companies to run a grounding wire along with their conductors (instead of using the dirt for a ground fault path) I will be happy to change my ways and run an egc in metal raceways (unless of course my boss finds out and fires me first for wasting his money)

 

[infinity]

If you guys will get the utility companies to run a grounding wire along with their conductors (instead of using the dirt for a ground fault path) I will be happy to change my ways and run an EGC in metal raceways (unless of course my boss finds out and fires me first for wasting his money)

Is the dirt really a path for the fault current or is the bonded neutral at the service responsible for that task?

 

[micromind]

I generally don't pull grounds in EMT unless it's required by code or specs., or looks likely to be ripped apart. Like a recpt. on a column in a warehouse, where it'll almost certainly be smashed at some point.

The city of Reno, where I do alot of work, has an ordinance that requires a ground in EMT when it's installed anywhere on the exterior of a building. Makes alot of sense to me. How many times have you seen EMT across a roof pulled apart at nearly every joint?

 

[nakulak]

Is the dirt really a path for the fault current or is the bonded neutral at the service responsible for that task?

don't know if I'm qualified to answer that, but, in view of the fact that
current is known to exist on the parallel path in the dirt (so called "stray current"), does it really matter which path is responsible for the task ?

 

[crossman]

I say it matters alot. The neutral path is most likely going to allow enough current to flow to trip the OCP. The path through the dirt may or may not do that. The path through the dirt may also set up some hazardous potential differences in the vicinity of the electrode which will persist until the fault is cleared.

The point is... on the line side of the service, the grounded conductor is not only a circuit conductor, it is also the path for ground fault current, in essence, it is the equipment grounding conductor (which may as well be more appropriately called the "equipment bonding conductor).

 

[nakulak]

I say it matters alot. The neutral path is most likely going to allow enough current to flow to trip the OCP. The path through the dirt may or may not do that. The path through the dirt may also set up some hazardous potential differences in the vicinity of the electrode which will persist until the fault is cleared.

The point is... on the line side of the service, the grounded conductor is not only a circuit conductor, it is also the path for ground fault current, in essence, it is the equipment grounding conductor (which may as well be more appropriately called the "equipment bonding conductor).

-are you saying that a neutral is going to trip a primary ?
-the whole fact that the dirt may or may not do it is part of why its dangerous to not have a separate utility grounding conductor
-the stray current due to poor utility neutrals causing current to flow through water mains and such is also another reason that the utility should have a grounding conductor, taking the current off all these unwanted things and putting it directly back to source