Equipment Grounding Conductor

[lmmillican]

I have an existing school that was built in late 70's or early 80's. For a summer renovation part of the scope was to replace a 400 amp and 600 amp 480 volt fusible panels with new panels and breakers. When the existing panels were opened it was discovered that the 400 amp was fed with 4 #500 KCM and 1 #6 ground and the 600 amp was fed with parallel sets of 4 #350 KCM and 1 #10 ground. The school district does not have money to re-pull the existing feeders with the appropriate sized equipment grounds (approximately 300 feet each). In looking at section 300.3, B (2) and 250.130 (C) it appears that running an equipment grounding conductor outside the raceway is not acceptable except for receptacles and branch circuits. I was just curious if anyone knew of anything else in the code that would allow the contractor to ground these panels so they would comply with code without having to re-pull new feeders. I forgot to mention that the raceway is below a suspended slab and is PVC.

 

[david]

I have an existing school that was built in late 70's or early 80's. For a summer renovation part of the scope was to replace a 400 amp and 600 amp 480 volt fusible panels with new panels and breakers. When the existing panels were opened it was discovered that the 400 amp was fed with 4 #500 KCM and 1 #6 ground and the 600 amp was fed with parallel sets of 4 #350 KCM and 1 #10 ground. The school district does not have money to re-pull the existing feeders with the appropriate sized equipment grounds (approximately 300 feet each). In looking at section 300.3, B (2) and 250.130 (C) it appears that running an equipment grounding conductor outside the raceway is not acceptable accept for receptacles and branch circuits. I was just curious if anyone knew of anything else in the code that would allow the contractor to ground these panels so they would comply with code without having to re-pull new feeders.

from my experience feeders installed in the 70's usually where in metal raceways.

 

[lmmillican]

When I got on site yesterday I was hoping they were installed in metal raceway but found out it was PVC. Not to say that the feeder conduit could have been changed at some point

 

[GoldDigger]

...
The school district does not have money to re-pull the existing feeders with the appropriate sized equipment grounds (approximately 300 feet each). In looking at section 300.3, B (2) and 250.130 (C) it appears that running an equipment grounding conductor outside the raceway is not acceptable except for receptacles and branch circuits. I was just curious if anyone knew of anything else in the code that would allow the contractor to ground these panels so they would comply with code without having to re-pull new feeders. ....

That is a tough one. Unfortunately anything except a metallic path back to the POCO transformer secondary is not likely to have a low enough resistance to qualify as a fault clearing path. And I do not know of any way to add an EGC totally separate from the feeder wires themselves.
The closest thing to not requiring an EGC is limited to separately derived systems, and I think installing a transformer would not help either, since there would have to be an EGC on both the primary and secondary side.

Maybe, if there is a way to convert the feeder into service conductors instead. That distance under the building could be allowable since the wires are buried under concrete. In that case you would just have to connect a GES to the neutral at the load end of the run.

 

[jap]

I have an existing school that was built in late 70's or early 80's. For a summer renovation part of the scope was to replace a 400 amp and 600 amp 480 volt fusible panels with new panels and breakers. When the existing panels were opened it was discovered that the 400 amp was fed with 4 #500 KCM and 1 #6 ground and the 600 amp was fed with parallel sets of 4 #350 KCM and 1 #10 ground. The school district does not have money to re-pull the existing feeders with the appropriate sized equipment grounds (approximately 300 feet each). In looking at section 300.3, B (2) and 250.130 (C) it appears that running an equipment grounding conductor outside the raceway is not acceptable except for receptacles and branch circuits. I was just curious if anyone knew of anything else in the code that would allow the contractor to ground these panels so they would comply with code without having to re-pull new feeders. I forgot to mention that the raceway is below a suspended slab and is PVC.

What are the Existing 400 and 600 amp fused panels fed from?

JAP>

 

[jap]

That is a tough one. Unfortunately anything except a metallic path back to the POCO transformer secondary is not likely to have a low enough resistance to qualify as a fault clearing path. And I do not know of any way to add an EGC totally separate from the feeder wires themselves.
The closest thing to not requiring an EGC is limited to separately derived systems, and I think installing a transformer would not help either, since there would have to be an EGC on both the primary and secondary side.

Maybe, if there is a way to convert the feeder into service conductors instead. That distance under the building could be allowable since the wires are buried under concrete. In that case you would just have to connect a GES to the neutral at the load end of the run.

There should not be an Equipment grounding conductor or Metallic path back the Power Company's Transformer for a fault clearing path.
The Neutral from the Power Company Transformer to the 1st means of disconnect serves that purpose.


JAP>

 

[lmmillican]

What are the Existing 400 and 600 amp fused panels fed from?

JAP>

The existing panels are fed from a 1600 amp Main Switchboard. The switchboard is grounded properly based on observations at the site.

 

[GoldDigger]

There should not be an Equipment grounding conductor or Metallic path back the Power Company's Transformer for a fault clearing path.
The Neutral from the Power Company Transformer to the 1st means of disconnect serves that purpose.


JAP>

I carefully stated "metallic path" and not EGC since the POCO neutral will be part of that path. When you say that there should not be a metallic path from EGC to transformer secondary, you are wrong. The path is not a dedicated path that does not also carry normal current, but it is a path.

 

[jap]

What metallic path between a padmount transformer and the first means of disconnect clears a fault?


JAP>

 

[GoldDigger]

What metallic path between a padmount transformer and the first means of disconnect clears a fault?


JAP>

Does not matter, as that is not usually covered by NEC.

Seriously, it depends on the fault. If the fault is hot to neutral, then the neutral is part of the fault clearing path and is covered by what I said. I have no problem with that.
If the fault is from hot to "earth" in some form, then it is the fault itself which is limiting the clearing current, not any path external to the fault. Chances are good the fault will not be cleared until something burns out or somebody sees the smoke and calls POCO.

Practically speaking, there is no reliable way to clear an overload, as opposed to a bolted fault, on the POCO side of the service disconnect.

 

[jap]

Does not matter, as that is not usually covered by NEC.

Seriously, it depends on the fault. If the fault is hot to neutral, then the neutral is part of the fault clearing path and is covered by what I said. I have no problem with that.
If the fault is from hot to "earth" in some form, then it is the fault itself which is limiting the clearing current, not any path external to the fault. Chances are good the fault will not be cleared until something burns out or somebody sees the smoke and calls POCO.

Practically speaking, there is no reliable way to clear an overload, as opposed to a bolted fault, on the POCO side of the service disconnect.

So again,,,, what metallic path between a pad mount transformer and the 1st means of disconnect clears a fault?

JAP>

 

[jap]

If I have pvc (Non Metallic) only running underground from the secondary of a pad mount transformer inside to a Main Distribution Panel , and the service conductors short out either line to ground or line to neutral,,,,, what metallic return path is there available to clear that fault other than the Neutral ?


JAP>

 

[GoldDigger]

So again,,,, what metallic path between a pad mount transformer and the 1st means of disconnect clears a fault?

JAP>

Same answer, but without the POCO references.

For an SDS, there will be some fault locations where there is not a metallic fault clearing path (in the specific case of a fault to earth.)
But for faults beyond the first OCPD there has to be an adequate path according to the NEC, which, except maybe when following European earthing standards, comes down in practice to a metallic path.

 

[jap]

Does not matter, as that is not usually covered by NEC.

Seriously, it depends on the fault. If the fault is hot to neutral, then the neutral is part of the fault clearing path and is covered by what I said. I have no problem with that.
If the fault is from hot to "earth" in some form, then it is the fault itself which is limiting the clearing current, not any path external to the fault. Chances are good the fault will not be cleared until something burns out or somebody sees the smoke and calls POCO.

Practically speaking, there is no reliable way to clear an overload, as opposed to a bolted fault, on the POCO side of the service disconnect.

So I guess your saying the metallic return path you brought up that's supposed to clear a fault from a power company's pad mount transformers to the first means of disconnect doesn't actually exist

 

[ActionDave]

So I guess your saying the metallic return path you brought up that's supposed to clear a fault from a power company's pad mount transformers to the first means of disconnect doesn't actually exist

I think what he is saying is nothing before the first disconnect matters.

As far as the NEC is concerned nothing exists before the first disconnect so there is nothing there to cause a fault or clear a fault.

 

[GoldDigger]

I think what he is saying is nothing before the first disconnect matters.

As far as the NEC is concerned nothing exists before the first disconnect so there is nothing there to cause a fault or clear a fault.

Which is why jap brought in the case of an SDS instead of a service. A fair point, and it comes down to there being no dependable fault clearing path for a ground fault between the transformer and the first disconnect. (Actually, it depends more on where the bonding jumper is than where the OCPD is, since at some fault level the primary OCPD to the SDS is likely to trip.)

 

[jap]

Which is why jap brought in the case of an SDS instead of a service. A fair point, and it comes down to there being no dependable fault clearing path for a ground fault between the transformer and the first disconnect. (Actually, it depends more on where the bonding jumper is than where the OCPD is, since at some fault level the primary OCPD to the SDS is likely to trip.)

I know this, as well as most others that are reading these posts, but for you to tell somebody bluntly that they're wrong is just wrong.


JAP>

 

[jap]

What I meant was you don't pull a ground wire or use a metallic raceway as an Equipment Grounding conductor as a fault clearing path between a power company's Transformer and the first means of Disconnect.

JAP>

 

[jap]

I think what he is saying is nothing before the first disconnect matters.

As far as the NEC is concerned nothing exists before the first disconnect so there is nothing there to cause a fault or clear a fault.

But there is something there guys,,,,please believe me not the NEC,,,, I know it,,,, I've seen it.....If we didn't have it we'd have no electricity.....

JAP>

 

[jap]

I have an existing school that was built in late 70's or early 80's. For a summer renovation part of the scope was to replace a 400 amp and 600 amp 480 volt fusible panels with new panels and breakers. When the existing panels were opened it was discovered that the 400 amp was fed with 4 #500 KCM and 1 #6 ground and the 600 amp was fed with parallel sets of 4 #350 KCM and 1 #10 ground. The school district does not have money to re-pull the existing feeders with the appropriate sized equipment grounds (approximately 300 feet each). In looking at section 300.3, B (2) and 250.130 (C) it appears that running an equipment grounding conductor outside the raceway is not acceptable except for receptacles and branch circuits. I was just curious if anyone knew of anything else in the code that would allow the contractor to ground these panels so they would comply with code without having to re-pull new feeders. I forgot to mention that the raceway is below a suspended slab and is PVC.

With all else aside, I would guess these 2 feeders were either changed or installed after the original school was built.
Generally, especially on a school project, there is a set of plans to go by and the wire size is indicated on the original drawings or the contractor is usually competent enough to know what size needs to be pulled.

Beyond all that more than likely it would have had to pass inspection back then also.

Seems odd since like others have mentioned, back then it was more common to see metallic conduit with no EGC pulled in with the feeder conductors at all.
Which if that were the case you wouldn't have the problem your faced with.

JAP>