Main panel grounding

[Smart $]

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".

Doesn't matter if the grounding bar is pre-install or furnished/bought as an add-in kit. Once installed per manufacturer's instructions, it is part of a listed assembly.

There is no requirement which says the grounding bar must be directly connected to the MBJ. 250.24(B) only specifies that the unspliced MBJ connect the enclosure and the EGC's to the grounded conductor (and there is no stipulation the grounding conductor entering the enclosure be directly connected to the MBJ)

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.

Absolutely correct.

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.

I can, and I am... but only under "compliant" circumstances, and this would be based on the bonding screw being a means of connection (under 250.8) rather than the MBJ. Additionally, a terminal bar is also a connection means itemized under 250.8. So the terminal bar must be directly connected to the MBJ and not connected to the grounded conductor except through the MBJ. Note a jumper bus, such as used in many cases to bridge grounded conductor terminal bars on opposing side of a panel, is not one of the itemized connection means under 250.8. If it were to be dubbed the MBJ, the bar on one side could be used for EGC's while the bar on the other side could be used for grounded conductors.

Now it is impossible to elaborate on each and every type of service panelboard here... so it comes down to evaluating each as it applies. And in that evaluation we must consider all the elements which must be in place to be compliant. Additionally we must keep in mind the concept behind each element...

IMO, the basal concept is to provide a star/single point connection for all grounded and grounding conductors... and we know that is impossible mechanically. In so much as separation is required, the concept is expanded upon so as to keep the separated connections of grounded conductors also separated from the separated connections of grounding conductors and bridge the two conglomerations by way of the MBJ.

Given that many service panelboard installers practice landing both EGC's and GNC's (grounded neutral conductors; not the brand name dietary supplements ) on the grounded conductor terminal bar(s) in semi-hap-hazard manner, I view that as an automatic violation of the expanded concept. However, I feel it will remain debatable as to its compliance.

 

[Volta]

He was assuming it to be a violation because it did not connect directly to the MBJ.

Yes.

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.

Doesn't matter if the grounding bar is pre-install or furnished/bought as an add-in kit. Once installed per manufacturer's instructions, it is part of a listed assembly.

We can't justify a splice that way. An irreversible crimp can satisfy 250.8(A)(1), in general, but that is still a splice, and while good enough for a GEC, won't work for a MBJ. Better that we claim that the group known as the 'equipment grounding conductor(s) and the service disconnect enclosure' be connected to the grounded conductor with an unspliced MBJ. I am ok with that.

There is no requirement which says the grounding bar must be directly connected to the MBJ. 250.24(B) only specifies that the unspliced MBJ connect the enclosure and the EGC's to the grounded conductor (and there is no stipulation the grounding conductor entering the enclosure be directly connected to the MBJ)

Or directly to the enclosure either, then. Can we agree that it must connect directly to the group of 'EGCs and enclosure'?

Absolutely correct.

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.

I can, and I am... but only under "compliant" circumstances, and this would be based on the bonding screw being a means of connection (under 250.8) rather than the MBJ. Additionally, a terminal bar is also a connection means itemized under 250.8.

This confuses me. If now we are talking about a grounded conductor terminal bar, we'd not be using 250.8.

So the terminal bar must be directly connected to the MBJ and not connected to the grounded conductor except through the MBJ. Note a jumper bus, such as used in many cases to bridge grounded conductor terminal bars on opposing side of a panel, is not one of the itemized connection means under 250.8. If it were to be dubbed the MBJ, the bar on one side could be used for EGC's while the bar on the other side could be used for grounded conductors.

I follow that, and agree, when using dual bars, a strap we call a MBJ, and a means of connection to the enclosure of, say, 250.8(A)(6), but my question was whether you could be accepting a single grounded conductor terminal bar to have EGCs connected to it. I didn't think you were.

Now it is impossible to elaborate on each and every type of service panelboard here... so it comes down to evaluating each as it applies. And in that evaluation we must consider all the elements which must be in place to be compliant. Additionally we must keep in mind the concept behind each element...

IMO, the basal concept is to provide a star/single point connection for all grounded and grounding conductors... and we know that is impossible mechanically.

Ok.

In so much as separation is required, the concept is expanded upon so as to keep the separated connections of grounded conductors also separated from the separated connections of grounding conductors and bridge the two conglomerations by way of the MBJ.

From a concept viewpoint, why do you feel that separation would be required?

Given that many service panelboard installers practice landing both EGC's and GNC's (grounded neutral conductors; not the brand name dietary supplements ) on the grounded conductor terminal bar(s) in semi-hap-hazard manner, I view that as an automatic violation of the expanded concept. However, I feel it will remain debatable as to its compliance.

 

[Smart $]

We can't justify a splice that way. An irreversible crimp can satisfy 250.8(A)(1), in general, but that is still a splice, and while good enough for a GEC, won't work for a MBJ. Better that we claim that the group known as the 'equipment grounding conductor(s) and the service disconnect enclosure' be connected to the grounded conductor with an unspliced MBJ. I am ok with that.

Or directly to the enclosure either, then. Can we agree that it must connect directly to the group of 'EGCs and enclosure'?

We don't have to justify a splice between grounding bar and an enclosure as a splice... assembled together (per manufacturer) they are a listed assembly, which is considered under 250.8(A)(7) a single connection. Furthermore, the bonding screw can also be considered within the sigle connection, as it too is part of the listed assembly. Thus the conductor that is to be dubbed the MBJ would be at the head end of the bonding screw (typically).

This confuses me. If now we are talking about a grounded conductor terminal bar, we'd not be using 250.8.

Why not. 250.8(A)(2) Terminal bars

A main bonding jumper and a system bonding
jumper shall be a wire, bus, screw, or similar suitable conductor.

Isn't a terminal bar essentially a bus with terminals.

I follow that, and agree, when using dual bars, a strap we call a MBJ, and a means of connection to the enclosure of, say, 250.8(A)(6), but my question was whether you could be accepting a single grounded conductor terminal bar to have EGCs connected to it. I didn't think you were.

I am/would, if it is compliant. For example, the bonding screw (enclosure only) has to be directly connected to it, and egc's must be landed adjacent thereto. Per definition, all the grounded conducotrs must be land to one side or the other of the egc's and the bonding screw. What it amounts to, a section or portion of the grounded conductor terminal bar is not the grounded conductor terminal bar but the MBJ. There cannot be grounded conductors to both electrical sides of the portion, or amid this portion. Also, in this case, the GEC could be connected anywhere along the bar.

From a concept viewpoint, why do you feel that separation would be required?

Not so much in the single panelboard case that we have been discussing, but say in the instance of a many-section switchgear/MCC with the main at one end. If we permitted landing GNC's on the same grounding bus as EGC's (which is usually bonded to the enclosure at each section), we would have GNC currents flowing through the enclosure. If we permitted landing EGC's on the isolated-from-ground busses of the GNC, there could be current flowing on or through many of the non-current-carrying metalic parts throughout the system. Current utilizes all available paths, not just the least resistive. Separating the grounded conductors from the grounding conductors prevents (in most cases) objectionable current.

 

[Volta]

Ok, We are getting close!

We don't have to justify a splice between grounding bar and an enclosure as a splice...

Agreed. The group of Non-Current Carrying Conductors (EGCs + enclosure) can be spliced together.

assembled together (per manufacturer) they are a listed assembly, which is considered under 250.8(A)(7) a single connection.

A permitted method of connecting grounding and bonding (not neccessarily Main) jumpers. I don't think we can call that unspliced, but, we don't need to.

Furthermore, the bonding screw can also be considered within the sigle connection, as it too is part of the listed assembly.

I don't think the listing matters. I mean, 110.3(B) of course, but so what if this stuff isn't listed. It amazes me how many things do not need listing. For 250.8(A)(7), ok, but you can do it with 250.8(A)(2)+(5) too. Remember the conductor(s) need not be in the list of 250.8, these are only the connection methods.

Thus the conductor that is to be dubbed the MBJ would be at the head end of the bonding screw (typically).


Why not. 250.8(A)(2) Terminal bars

​

Isn't a terminal bar essentially a bus with terminals.

Yes, but 250.8 is for the permitted method to connect grounding conductors, not grounded (circuit conductors).

I am/would, if it is compliant. For example, the bonding screw (enclosure only) has to be directly connected to it, and egc's must be landed adjacent thereto. Per definition, all the grounded conducotrs must be land to one side or the other of the egc's and the bonding screw. What it amounts to, a section or portion of the grounded conductor terminal bar is not the grounded conductor terminal bar but the MBJ. There cannot be grounded conductors to both electrical sides of the portion, or amid this portion. Also, in this case, the GEC could be connected anywhere along the bar.

Ok. Now I think we have hammered out a basic agreement. Some central point of a grounded conductor terminal strip (usually a neutral bus/bar) can serve as a MBJ, that point can be where the connection to the enclosure is made (though whether or not the manufacturers typically pick that location for the 250.8(A)(5) screw is a separate problem), with grounded conductors on the "line" side of that point, EGCs on the "load" side, and the GEC anywhere on that bus.

Not so much in the single panelboard case that we have been discussing, but say in the instance of a many-section switchgear/MCC with the main at one end. If we permitted landing GNC's on the same grounding bus as EGC's (which is usually bonded to the enclosure at each section), we would have GNC currents flowing through the enclosure. If we permitted landing EGC's on the isolated-from-ground busses of the GNC, there could be current flowing on or through many of the non-current-carrying metalic parts throughout the system. Current utilizes all available paths, not just the least resistive. Separating the grounded conductors from the grounding conductors prevents (in most cases) objectionable current.

Think big! I like it!