Equipment Bonding Jumper

[crossman gary]

Two weeks ago I would have sworn it was an EGC, and that in the sections concerning EGCs, there was a reference to use 250.122 for feeders and branch circuits, and to use 250.66 or the 12.5% rule for EGCs on the line side of the service disconnect or first disconnecting means on the SDS.

I was wrong! Years of assumptions down the drain and now I have to rethink all this.

 

[crossman gary]

Ooops. My answer to charlie's Question 6 and response to RUWired is in error. You are correct. It is an EBJ, but not one which meets the definition. It is an EBJ as implied by section statements only... namely 250.30(A)(2), and thus 250.102(C).

Smart, I agree, there is something out of whack here. The definition doesn't match with the sections. And I'm not even sure of the intent here. Is an EGC only for use on the load side of the first disconnect?

I always have considered the panel enclosures and raceways and such to be equipment grounds, even at the service or transformer.

Hmmm..... gotta do some checking. I am betting there are conflicts in the code concerning this.

 

[don_resqcapt19]

Questions:
1. Would I be right in calling ?conductor number 1? a ?grounding electrode conductor??
2. Would I be right in calling ?conductor number 2? a ?system bonding jumper??
3. Would I be right in declaring that the existence of ?conductors number 1 and 2? causes the N-G bonding to have taken place at the transformer?
4. Would I be right in saying that, at the transformer, I could connect ?conductor number 3? to either the center point of the transformer secondary, or to the transformer?s case, as they are essentially the same point now?
5. Would I be right is saying that, at the distribution panel, I connect ?conductor number 3? to the ground bar?
6. What is the correct name for ?conductor number 3??

1) This is the GEC assuming that the bus that it is connected to complies with 250.64(F)(3).
2) This is an Equipment bonding conductor. It does not connect the grounded conductor to the EGCs and that is the function of the system bonding jumper.
3)Yes.
4) Conductor #3 is the system bonding jumper and it must connect to the grounded conductor at the transformer.
5) Yes.
6) This conductor is the system bonding jumper.

 

[crossman gary]

From the center point of the transformer secondary, I run ?conductor number 2? to the case of the transformer.

Would I be right in calling ?conductor number 2? a ?system bonding jumper?

There is absolutely no doubt (in my mind) that conductor # 2 is the system bonding jumper.

There is no way that conductor 3 can be the system bonding jumper.

250.30(A)(1) says that the system bonding jumper is used to connect EGCs to the grounded conductor and that his connection must be made at any single point from the source to the first disconnect. By single point, the intention, in my opinion, is that the system bonding jumper must be contained within the same piece of equipment. In this case, it can be in the xfmr, or it can be in the panel, but there is no way it can be run from one enclosure through conduit to another enclosure.

The SBJ in a SDS is the equivalent ofthe MBJ at the service.

 

[crossman gary]

But over the past two weeks, I admit that this forum has me rethinking about just exactly what is the EGC at an SDS. I always took it that the xfmr case and the panel enclosure were equipment grounds, and that there would be an EGC in between them.

Yes, I already mentioned this.

 

[Smart $]

I am betting there are conflicts in the code concerning this.

There certainly are conflicts. You can start at 250.102(C)... I forget the subsection numbers right now, but one is regarding EBJ on line side of service disconnect, the next on the load side... and 250.30(C)(#>???re:EBJ) also sends one to this section regarding the bonding of an SDS. And all this does not meet the definition of an EBJ (as I interpret it).

 

[Smart $]

There certainly are conflicts. ... And all this does not meet the definition of an EBJ (as I interpret it).

Forgot to say, if a grounding conductor is run between the transformer and the first disconnect without meeting the defintion of an EBJ, then it is an EGC... so we're back to my incorrect answer earlier actually being correct using this logic :grin:

Offhand I can't recall there actually being an explicit requirement to run an EBJ... whereas there are requirements for equipment grounding. Can someone point me to an explicit requirement for running an EBJ...???

 

[don_resqcapt19]

There is absolutely no doubt (in my mind) that conductor # 2 is the system bonding jumper.

And there is no doubt in my mind that it can't be the system bonding jumper per the same section that you cited. It does not connect the grounded conductor to the equipment grounding conductors. Wire #3 does that in Charlie's set up.

 

[Smart $]

And there is no doubt in my mind that it can't be the system bonding jumper per the same section that you cited. It does not connect the grounded conductor to the equipment grounding conductors. Wire #3 does that in Charlie's set up.

If Conductor 2 connects C-tap to T-case (or a grounding bar/bus connected to case) and Conductor 3 is connected to T-case end of Conductor 2, then Conductor 2 is an SBJ.

However, if Conductor 3 were connected to the C-tap end of Conductor 2, Conductor 2 would be an EGC.

In either case, Conductor 3 would be either an EBJ or an EGC (the jury within myself is still out on this one).

Note: for the sake of discussion, the C-tap could interchangeably be X0.

 

[Smart $]

If Conductor 2 connects C-tap to T-case (or a grounding bar/bus connected to case) and Conductor 3 is connected to T-case end of Conductor 2, then Conductor 2 is an SBJ.

However, if Conductor 3 were connected to the C-tap end of Conductor 2, Conductor 2 would be an EGC.

In either case, Conductor 3 would be either an EBJ or an EGC (the jury within myself is still out on this one).

Note: for the sake of discussion, the C-tap could interchangeably be X0.

Pictures :grin:

Case #1

Case #2

 

[don_resqcapt19]

Smart,
Thanks for the nice drawings of this.
In both cases, I don't think that there is any question that conductor #1 is the GEC. In case 1, #2 is a system bonding jumper and #3 is an equipment bonding jumper.
In case 2, #2 is an equipment bonding jumper and #3 is a system bonding jumper.
I say equipment bonding jumper in place of equipment grounding conductor, because it is my opinion that EGCs do not exist on the line side of the SDS OCPD.

 

[Smart $]

In both cases, I don't think that there is any question that conductor #1 is the GEC.

Agreed.

In case 1, #2 is a system bonding jumper and #3 is an equipment bonding jumper.
...
I say equipment bonding jumper in place of equipment grounding conductor, because it is my opinion that EGCs do not exist on the line side of the SDS OCPD.

I can live with that, but I still say calling it such and having it meet the definition of such is contradictory. If it were made more clear that it bonds the primary grounding system to the secondary grounding system, then we'd have no room for disagreement as it would then clearly meet the definition. However, if a bond to the primary grounding system were made through connection to X0 in the pictures, I would still have to call Conductor #2 in Case #2 an EGC.

In case 2, #2 is an equipment bonding jumper and #3 is a system bonding jumper.

I have to disagree with you here regarding #3. I've always had the impression an SBJ is limited [though quite vaguely] to the extents of one piece of equipment. There are accepted proposals for the 2011 edition that, if passed, will clarify this perspective at least a little bit... :grin:

 

[crossman gary]

I was always under the impression that xfmr enclosures, panel enclosures, switchboard enclosures, etc, were part of the EGC system.

For example, if we have a feeder in RMC, and the feeder does not have a wire type EGC, and we take the feeder to a subpanel, we can certainly attach a ground bar to the panel enclosure and connect branch circuit wire type EGCs to that. The panel enclosure is no doubt extending the feeder EGC to the BC EGC.

As evidenced in this thread, if intelligent people are disagreeing/not certain about code rules that are very basic, then something is wrong with the way the code is written. There is a definite discontinuity between the Art 100 definitions and code sections.