Main panel grounding

[Volta]

Well, let's work it through.
-Section 250.24(B) has us using the MBJ to connect the EGCs and enclosure to the grounded conductor.
-250.24(C) has us using the MBJ to connect the enclosure to the grounded conductor.
-Art 100 definition has us using the MBJ to connect the EGC to the grounded conductor.

All three similar descriptions have us connecting the grounded conductor to some combination of the enclosure and/or the EGCs with the MBJ. If the terminal strip for the grounded conductor can be considered similar to a "bus" per 250.28(A) the common method would be compliant. I think that it is, and that may be our best way out.

If not though, and one uses a factory supplied screw or offset bar to bond the grounded terminal bar to the enclosure, and installs a separate EGC bar, we have two options.
1. Install the correct size wire, bus, or screw between the grounded conductor directly (with a split bolt or similar) and the EGC bar, or
2. Accept that the enclosure material is the second "suitable conductor" between the grounded and grounding conductor(s).

In either case, the grounded conductor is often connected to a terminal bar. If you accept the factory supplied MBJ (screw or bar), then for some short distance, you are accepting that the strip with lug qualifies as a MBJ bus, at least from the source terminal to the bonding connection. If that is so, the the EGCs are in fact connected to the MBJ bus.

 

[Smart $]

Well, let's work it through.
-Section 250.24(B) has us using the MBJ to connect the EGCs and enclosure to the grounded conductor.
-250.24(C) has us using the MBJ to connect the enclosure to the grounded conductor.
-Art 100 definition has us using the MBJ to connect the EGC to the grounded conductor.

All three similar descriptions have us connecting the grounded conductor to some combination of the enclosure and/or the EGCs with the MBJ. If the terminal strip for the grounded conductor can be considered similar to a "bus" per 250.28(A) the common method would be compliant. I think that it is, and that may be our best way out.

If not though, and one uses a factory supplied screw or offset bar to bond the grounded terminal bar to the enclosure, and installs a separate EGC bar, we have two options.
1. Install the correct size wire, bus, or screw between the grounded conductor directly (with a split bolt or similar) and the EGC bar, or
2. Accept that the enclosure material is the second "suitable conductor" between the grounded and grounding conductor(s).

In either case, the grounded conductor is often connected to a terminal bar. If you accept the factory supplied MBJ (screw or bar), then for some short distance, you are accepting that the strip with lug qualifies as a MBJ bus, at least from the source terminal to the bonding connection. If that is so, the the EGCs are in fact connected to the MBJ bus.

You are examining this fully and I welcome the attitude

Now consider the fact, per service disconnecting means enclosure (and I am assuming herein and thereafter, until stated to the contrary, we are discussing a service panelboard in which the main breaker is the service disconnecting means), you are only permitted one MBJ in the enclosure and the one MBJ cannot be spliced [250.24(B)]. If the enclosure is bonded to the neutral busbar using a screw/wire/strap/busbar, that is the MBJ. If you land EGC's on the neutral busbar, they are on the wrong end of the MBJ.

If you could manage to have the MBJ as a terminal busbar, you could then land your EGC's and branch-circuit grounded conductors thereto. In all panelboards I've seen, no part of the neutral bar(s) is(are) in direct contact with the enclosure. So I don't see how the neutral busbar can ever be the MBJ.

 

[Volta]

You are examining this fully and I welcome the attitude

Now consider the fact, per service disconnecting means enclosure (and I am assuming herein and thereafter, until stated to the contrary, we are discussing a service panelboard in which the main breaker is the service disconnecting means)

Ok.

you are only permitted one MBJ in the enclosure

Maybe, but I can't find a specific restriction. Plurals are used in 250.28. I agree in principle, though.

and the one MBJ cannot be spliced [250.24(B)].

True, that one cannot be spliced.

If the enclosure is bonded to the neutral busbar using a screw/wire/strap/busbar, that is the MBJ.

That would be a MBJ. That meets the 250.24(C) requirement (grounded to enclosure).

If you land EGC's on the neutral busbar, they are on the wrong end of the MBJ.

They may be.

If you could manage to have the MBJ as a terminal busbar, you could then land your EGC's and branch-circuit grounded conductors thereto. In all panelboards I've seen, no part of the neutral bar(s) is(are) in direct contact with the enclosure. So I don't see how the neutral busbar can ever be the MBJ.

Ok, I agree. It could often be a violation to land the EGCs in a "neutral" bar.

I can conceive of no reasonable means to connect the grounded conductor (if an insulated terminal bus) both to the enclosure and to the EGC(s) through an unspliced MBJ. Wire to lug/terminal to screw to enclosure may work for the Art. 100 and Section 250.24(C) MBJs, but not for 250.24(B). Those multiple series connections are splices. We could weld the jumper to the enclosure, but that is unreasonable. :roll:

So unless this were to be rephrased, we will (almost) have to pick our violation of choice. Either we splice the bond to the enclosure, via screws and lugs, or we don't use a MBJ between the grounded and grounding.

On the other hand, if we allow more than one MBJ in an enclosure, then a screw can be used to connect to the enclosure, while some section of the neutral bus serves as a bond to the EGCs. Electrically, this normal everyday method is best, but I think you are right that it does not allow the MBJ to serve its stated purpose.

 

[Smart $]

Let's clarify one thing before we move on...

...

you are only permitted one MBJ in the enclosure

Maybe, but I can't find a specific restriction. Plurals are used in 250.28. I agree in principle, though.

The reason plurals are used in 250.28 is because you can have more than one service/system disconnecting means in separate enclosures. Probably would have been more appropriate to put the "s" in parentheses to indicate singular being a possibility also. Using only the plural in 250.28 could be interpretted (errantly, btw) as requiring more than one always.

If you land EGC's on the neutral busbar, they are on the wrong end of the MBJ.

They may be.

Come on now. 250.24(B) uses the singular term "unspliced main bonding jumper" and it is to connect EGC's AND enclosure TO the grounded conductor. How can EGC's be connected to the neutral "grounded conductor" busbar and the MBJ both especially when the neutral busbar is not the MBJ?

I think many believe the neutral busbar is because the GEC is terminated to it. But that is simply not true.

Ok, I agree. It could often be a violation to land the EGCs in a "neutral" bar.

"Often"??? Come again! I have yet to speculate one possible scenario where it is not a violation, and you have yet to provide a potentially feasible one for consideration. Though you immediately resort to...

I can conceive of no reasonable means to connect the grounded conductor (if an insulated terminal bus) both to the enclosure and to the EGC(s) through an unspliced MBJ. Wire to lug/terminal to screw to enclosure may work for the Art. 100 and Section 250.24(C) MBJs, but not for 250.24(B). Those multiple series connections are splices. We could weld the jumper to the enclosure, but that is unreasonable. :roll:

Yes, welding is quite a stretch

So unless this were to be rephrased, we will (almost) have to pick our violation of choice. Either we splice the bond to the enclosure, via screws and lugs, or we don't use a MBJ between the grounded and grounding.

And how do you propose we do the latter?

On the other hand, if we allow more than one MBJ in an enclosure, then a screw can be used to connect to the enclosure, while some section of the neutral bus serves as a bond to the EGCs. Electrically, this normal everyday method is best, but I think you are right that it does not allow the MBJ to serve its stated purpose.

To say the scenario we are attacking is unsafe, I cannot. Yet it sounds like you are at least beyond the midpoint of believing me that it is a violation

 

[mcclary's electrical]

Let's clarify one thing before we move on...


The reason plurals are used in 250.28 is because you can have more than one service/system disconnecting means in separate enclosures. Probably would have been more appropriate to put the "s" in parentheses to indicate singular being a possibility also. Using only the plural in 250.28 could be interpretted (errantly, btw) as requiring more than one always.


Come on now. 250.24(B) uses the singular term "unspliced main bonding jumper" and it is to connect EGC's AND enclosure TO the grounded conductor. How can EGC's be connected to the neutral "grounded conductor" busbar and the MBJ both especially when the neutral busbar is not the MBJ?

I think many believe the neutral busbar is because the GEC is terminated to it. But that is simply not true.


"Often"??? Come again! I have yet to speculate one possible scenario where it is not a violation, and you have yet to provide a potentially feasible one for consideration. Though you immediately resort to...

Yes, welding is quite a stretch


And how do you propose we do the latter?


To say the scenario we are attacking is unsafe, I cannot. Yet it sounds like you are at least beyond the midpoint of believing me that it is a violation

I'm beyond half way. I'm with you.

 

[iwire]

Ground up or Ground down?

 

[Smart $]

Ground up or Ground down?

Up before 5 am on a Saturday and you ask this question???

Now we know why you're not getting enough sleep

 

[Volta]

Yeah, past the midpoint, I'm in your camp. But I'm a recent arrival, so I'm still testing the waters a bit .

Let's clarify one thing before we move on...


The reason plurals are used in 250.28 is because you can have more than one service/system disconnecting means in separate enclosures. Probably would have been more appropriate to put the "s" in parentheses to indicate singular being a possibility also. Using only the plural in 250.28 could be interpretted (errantly, btw) as requiring more than one always.

Ok.

Come on now. 250.24(B) uses the singular term "unspliced main bonding jumper" and it is to connect EGC's AND enclosure TO the grounded conductor. How can EGC's be connected to the neutral "grounded conductor" busbar and the MBJ both especially when the neutral busbar is not the MBJ?

I think many believe the neutral busbar is because the GEC is terminated to it. But that is simply not true.

I know that we did agree that this discussion would consider a MB service panel. But with Main Lugs- Exception No. 1 does not require the MBJ to connect the grounded conductor to anything other than the enclosure. Why?

"Often"??? Come again! I have yet to speculate one possible scenario where it is not a violation, and you have yet to provide a potentially feasible one for consideration. Though you immediately resort to...

Yes, welding is quite a stretch

Oh, I think that Exception No. 1 is the only reason for "often". That, and I am not always an early-adopter.

And how do you propose we do the latter?

Just the way it is done now, a screw from the grounded to the enclosure, and the EGCs landed on the grounded terminal strip.

To say the scenario we are attacking is unsafe, I cannot. Yet it sounds like you are at least beyond the midpoint of believing me that it is a violation

Yes. In a main breaker service panel, looks like it really is.

In MLO panels, I don't know. Tell me what Exception No. 1 to 250.24(B) means to you. I think it would allow EGCs to be connected to the grounded conductor bus with no MBJ between.

What would you propose as a solution? I think that we would want to continue the standard practice and reword 250.24(B), rather than require that the EGCs be terminated in an additional bar, as no safety would be realized that way, and the unspliced MBJ between would simply add two more connection points.

 

[Volta]

Ground up or Ground down?

I know we've hijacked this a bit, but are you trying to get this thread closed? :grin:

 

[Smart $]

Yeah, past the midpoint, I'm in your camp. But I'm a recent arrival, so I'm still testing the waters a bit .

By all means, please continue. You are probably asking all the questions the non-participant readers have in their minds

...
I know that we did agree that this discussion would consider a MB service panel. But with Main Lugs- Exception No. 1 does not require the MBJ to connect the grounded conductor to anything other than the enclosure. Why?

Oh, I think that Exception No. 1 is the only reason for "often". That, and I am not always an early-adopter.

Just the way it is done now, a screw from the grounded to the enclosure, and the EGCs landed on the grounded terminal strip.


Yes. In a main breaker service panel, looks like it really is.

In MLO panels, I don't know. Tell me what Exception No. 1 to 250.24(B) means to you. I think it would allow EGCs to be connected to the grounded conductor bus with no MBJ between.

250.24(B) Exception #1 doesn't say what you think it says. It is regarding a "service assembly" (aka service-rated panelboard, for one) where the enclosure has or may contain one or more service/system disconnecting means. Yes, many are in essence an MLO "panel", but not all. What the Exception actually says is that only one MBJ is necessary, i.e. you don't have to install one for each service/system disconnecting means. I don't know for certain why EGC's are omitted from the Exception. The best I can do there is speculate, so I'll avoid that for the time being.

What would you propose as a solution? I think that we would want to continue the standard practice and reword 250.24(B), rather than require that the EGCs be terminated in an additional bar, as no safety would be realized that way, and the unspliced MBJ between would simply add two more connection points.

While I understand your "safer" perspective, it is not all encompassing. And I don't see the violating past and current practice as unsafe in and of itself. However, I would prefer the wording to only be more clear that it is a violation. As the violations dwindle, unqualified and DIY'ers will be less likely to assume the practice is safe to do in subpanels. Besides, how much more difficult is it to install a grounding bar kit if the panelboard is not furnished with one. Then again, making the violation more evident will perhaps force manufacturers into pre-installing the grounding busbars.

 

[Volta]

By all means, please continue. You are probably asking all the questions the non-participant readers have in their minds


250.24(B) Exception #1 doesn't say what you think it says. It is regarding a "service assembly" (aka service-rated panelboard, for one) where the enclosure has or may contain one or more service/system disconnecting means. Yes, many are in essence an MLO "panel", but not all. What the Exception actually says is that only one MBJ is necessary, i.e. you don't have to install one for each service/system disconnecting means.

You are right.

I don't know for certain why EGC's are omitted from the Exception. The best I can do there is speculate, so I'll avoid that for the time being.

I don't either, but to borrow Bob's phrase, it says what it says, and it doesn't say what it doesn't say. Per that exception: Two to six disconnects (they shouldn't have written 'means', compared to 230.71(A), but that's ok), in one enclosure listed for same, only requires the MBJ to connect the grounded conductor to the enclosure. No reference to the EGCs.

While I understand your "safer" perspective, it is not all encompassing. And I don't see the violating past and current practice as unsafe in and of itself.

Agreed.

However, I would prefer the wording to only be more clear that it is a violation. As the violations dwindle, unqualified and DIY'ers will be less likely to assume the practice is safe to do in subpanels.

True, if we went that way (separate bars) rather than rewording to remove the violation. As it is electrically sound to land the EGCs on the grounded bus in a service disconnect enclosure, and simply use the MBJ to bond the enclosure, I feel that we would be asking too much to require separate EGC bars to remove the violation. Leave the Article 100 definition as is, but add a different name for the Enclosure Bonding Jumper, and reword 250.24(B) and (C) accordingly.

Besides, how much more difficult is it to install a grounding bar kit if the panelboard is not furnished with one.

Not much more. But aside from showing future unqualified persons that we never land EGCs on the grounded bus, what purpose would it serve?

Then again, making the violation more evident will perhaps force manufacturers into pre-installing the grounding busbars.

So, in summary, it is a violation of Section 250.24(B) to connect EGC(s) to a Grounded Condutor's bus or terminal bar in a service disconnecting means that contains only one disconnect, due to the fact that the MBJ is not used to connect the EGC to the Grounded Conductor. Right?

Can you develop similar wording to show the violation with multiple disconnects in a single enclosure?

 

[Smart $]

You are right.

I don't either, but to borrow Bob's phrase, it says what it says, and it doesn't say what it doesn't say. Per that exception: Two to six disconnects (they shouldn't have written 'means', compared to 230.71(A), but that's ok), in one enclosure listed for same, only requires the MBJ to connect the grounded conductor to the enclosure. No reference to the EGCs.


Agreed.

True, if we went that way (separate bars) rather than rewording to remove the violation. As it is electrically sound to land the EGCs on the grounded bus in a service disconnect enclosure, and simply use the MBJ to bond the enclosure, I feel that we would be asking too much to require separate EGC bars to remove the violation. Leave the Article 100 definition as is, but add a different name for the Enclosure Bonding Jumper, and reword 250.24(B) and (C) accordingly.

Not much more. But aside from showing future unqualified persons that we never land EGCs on the grounded bus, what purpose would it serve?


So, in summary, it is a violation of Section 250.24(B) to connect EGC(s) to a Grounded Condutor's bus or terminal bar in a service disconnecting means that contains only one disconnect, due to the fact that the MBJ is not used to connect the EGC to the Grounded Conductor. Right?

Can you develop similar wording to show the violation with multiple disconnects in a single enclosure?

Now I think I know why the Exception doesn't mention EGC's. In using a premise based on "Bob's phrase", you have to remember you are applying it to an Exception to the rule. It says one MBJ to bond enclosure to grounded conductor(s). It does not say you cannot/shall not use one MBJ for each service disconnecting means. It is just letting one-for-all be adequate. Additionally, it does not say where EGC's must land... therefore landing of the EGC's is still mandated by the section's general rule, which squarely puts it back on an MBJ's end opposite the grounded conductor(s)... and in the two-to-six-in-one-assembly case, more than one MBJ can be used.

At this point, I'm not all that concerned with rewording. I'm more interested in what the general consensus is among forum members

 

[Volta]

Now I think I know why the Exception doesn't mention EGC's. In using a premise based on "Bob's phrase", you have to remember you are applying it to an Exception to the rule. It says one MBJ to bond enclosure to grounded conductor(s). It does not say you cannot/shall not use one MBJ for each service disconnecting means. It is just letting one-for-all be adequate. Additionally, it does not say where EGC's must land... therefore landing of the EGC's is still mandated by the section's general rule, which squarely puts it back on an MBJ's end opposite the grounded conductor(s)... and in the two-to-six-in-one-assembly case, more than one MBJ can be used.

At this point, I'm not all that concerned with rewording. I'm more interested in what the general consensus is among forum members

Well, I think we need to decide whether or not it can ever be permitted to have more than one MBJ in an enclosure.

If we may have more than one "main" jumper in an enclosure, then the one bonding the enclosure need not be the same as the one bonding the EGCs.

If we may not have more than one MBJ, then the exception would not be needed at all, unless perhaps it is to allow for a Main Lug Panel "assembly listed for use as service equipment" to not need provisions for a separate EGC terminal bar as most other (non-service rated) main lug only panels would. Wherein CMP 5 intends for the MBJ to simply connect the enclosure to the grounded conductor.

 

[LarryFine]

Ground up or Ground down?

Careful, the Mod Squad doesn't like that one!



Oh, it's you, Bob, setting a good example for the rest of us.

 

[LarryFine]

But with Main Lugs- Exception No. 1 does not require the MBJ to connect the grounded conductor to anything other than the enclosure. Why?

In my opinion, when the jumper is used to bond the panel, it's not the MBJ, the neutral bus itself is. If the EGC's and GEC's are landed on buses that are bolted to the encloisure, then the jumper is the MBJ, but along with the enclosure itself.

Just the way it is done now, a screw from the grounded to the enclosure, and the EGCs landed on the grounded terminal strip.

Agreed, and again, the neutral bus is also the MBJ, because it is what connects the GEC's and EGC's to the neutral. My apologies if any of this is repetitive; I didn't read every post through.

 

[Smart $]

In my opinion, when the jumper is used to bond the panel, it's not the MBJ, the neutral bus itself is. If the EGC's and GEC's are landed on buses that are bolted to the encloisure, then the jumper is the MBJ, but along with the enclosure itself.

Agreed, and again, the neutral bus is also the MBJ, because it is what connects the GEC's and EGC's to the neutral. My apologies if any of this is repetitive; I didn't read every post through.

Hate to say it, but you are wrong. The GEC is required to be connected to the grounded-conductor end of the MBJ. It is only through exception that it is permitted on the other end.

Then we get back to the MBJ has to be unspliced.

***Running late for a dinner engagement. Will add more when I return...

 

[LarryFine]

Hate to say it, but you are wrong. The GEC is required to be connected to the grounded-conductor end of the MBJ. It is only through exception that it is permitted on the other end.

Then we get back to the MBJ has to be unspliced.

Just scanning through 250.24(A)(4) and 250.28(A), I must disagree with your disagreement.

 

[Smart $]

First, I must apologize for misleading. In my haste I referred to an SDS requirement, not a service requirement per se...

The GEC is required to be connected to the grounded-conductor end of the MBJ. It is only through exception that it is permitted on the other end.

The preceding statement stems from...

250.30(A)...
(3) Grounding Electrode Conductor, Single Separately
Derived System. A grounding electrode conductor for a
single separately derived system shall be sized in accordance
with 250.66 for the derived phase conductors and shall
be used to connect the grounded conductor of the derived
system to the grounding electrode as specified in
250.30(A)(7). This connection shall be made at the same
point on the separately derived system where the system
bonding jumper is connected.

Exception No. 1: If the system bonding jumper specified in
250.30(A)(1) is a wire or busbar, it shall be permitted to
connect the grounding electrode conductor to the equipment
grounding terminal, bar, or bus, provided the equipment
grounding terminal, bar, or bus is of sufficient size for
the separately derived system.

This may come up in a later discussion... but for now, let's get back to a service system...

Just scanning through 250.24(A)(4) and 250.28(A), I must disagree with your disagreement.

Looking past my error, 250.24(A)(4) is the correct place, and a rule rather than the exception to the rule. However, note the use of terminology as emphasiszed in quote below.

(4) Main Bonding Jumper asWire or Busbar. Where the
main bonding jumper specified in 250.28 is a wire or busbar
and is installed from the grounded conductor terminal
bar or bus to the equipment grounding terminal bar or bus
in the service equipment, the grounding electrode conductor
shall be permitted to be connected to the equipment
grounding terminal, bar, or bus to which the main bonding
jumper is connected.

Note it says "shall be permitted". So even though this is not an exception, it is an option under a certain set of circumstances (and quite similar to 250.30(A)(3) and its Exception #1 mentioned above, so I wasn't really that far off ).

Next, you stated in your reply to Volta, "the neutral bus is also the MBJ". How can this be when in 250.28(A)(4), for example, four distinctly different terms are given to each item? Let's see, you're saying the grounded conductor terminal bus or bar is also the main bonding jumper and is also the equipment grounding terminal, bar, or bus. WHOA!!! This is giving me a headache. What was that again that "shall be permitted" to be connected to what???

Sort of OT, but yet goes to cohesive interpretation of the Code: which side of the fence are you on regarding using a GEC also as an EGC, say between a main panel and an SDS xfmr? For the record I'm already on record as approving coincidental usage.

Then we get back to the MBJ cannot be spliced [250.24(B)]. Wouldn't your premise mean that if you had a neutral bar in both gutters (i.e. two bars with a jumper bus between them), you could only use the one that the incoming grounded conductor is attached to for EGC's, and the GEC must attach to that bar in order to do so. What if it's a SQD 1? loadcenter where the incoming grounded conductor is connected to the jumper bus???

Well, enough for now... gotta get rid of this headache before posting more...

 

[Smart $]

Well, enough for now... gotta get rid of this headache before posting more...

Hmmm... No additional posts since yesterday. Does that mean the subject is dead???

Well, I'll add something for Volta. He mentioned choosing our violation, one of which was using the manufacturers grounding bar (pre-installed or kit) as one of the two options. The news is, this installation method is not a violation. He was assuming it to be a violation because it did not connect directly to the MBJ. It is not a violation because one of the permitted types of connections are listed assemblies. The grounding bar(s) installed by manufacturer or per instruction therefrom is(are) part of a listed assembly and thus compliant.

Now I know someone is likely to bring up that the grounded conductor terminal or bus is part of a listed assembly... and they would be correct. The only problem is that "listed assembly" as used for the grounding bar is for connections [250.8], and not applicable to grounding and bonding equipment. Which is to say, yes there may be a part of the grounded terminal bus that can be used for EGC's, but only where there is no "splice" (aka connection) involved between the EGC and the conductor performing the function of MBJ.

 

[Volta]

Hmmm... No additional posts since yesterday. Does that mean the subject is dead???

Not at all, we were just waiting for you.

Well, I'll add something for Volta. He mentioned choosing our violation, one of which was using the manufacturers grounding bar (pre-installed or kit) as one of the two options. The news is, this installation method is not a violation. He was assuming it to be a violation because it did not connect directly to the MBJ. It is not a violation because one of the permitted types of connections are listed assemblies. The grounding bar(s) installed by manufacturer or per instruction therefrom is(are) part of a listed assembly and thus compliant.

We know that the grounding bar is not normally pre-installed by the manufacturer in a panel with a main breaker. We would have to define "unspliced" to settle on a connection from the grounded conductor to MBJ (screw or strap, for instance) to the enclosure to an EGC bar as being considered "unspliced".
We know per 250.24(A)(4) that such a connection is not sufficient to allow the GEC to be connected there, it would need to be a wire or busbar.

Now I know someone is likely to bring up that the grounded conductor terminal or bus is part of a listed assembly... and they would be correct. The only problem is that "listed assembly" as used for the grounding bar is for connections [250.8], and not applicable to grounding and bonding equipment. Which is to say, yes there may be a part of the grounded terminal bus that can be used for EGC's, but only where there is no "splice" (aka connection) involved between the EGC and the conductor performing the function of MBJ.

I am having trouble understanding this, I know you can't be accepting the grounded bar for the EGCs. In that instance, a section of the grounded bar is performing the Article 100 function of the MBJ, and the factory provided 'MBJ' (screw or strap) is bonding the enclosure. That section of the grounded bar is unspliced, even if hard to draw the dividing point on.