Main Bonding Jumper

[pete m.]

Would it be a violation of the NEC to use the main bonding jumper as a current carrying conductor for the unbalanced neutral load in a main breaker loadcenter? ( By the way this is not a rhetorical question, there is more to the story. Just wanted some professional opinions before I go any further )
Pete

[ May 06, 2003, 10:56 PM: Message edited by: pete m. ]

 

[bennie]

Re: Main Bonding Jumper

Pete: Are you referring to a Siemans panel with a removable bus tie between the two busses on each side of the panel?

 

[don_resqcapt19]

Re: Main Bonding Jumper

The main bonding jumper should not be able to carry load current if properly installed. It connects the grounded conductor to the enclosure and equipment grounding conductors.
Don

 

[pete m.]

Re: Main Bonding Jumper

The loadcenter I am referring to is the Cutler-Hammer style residential loadcenter (it is a fairly new design, sorry I do not have any catalog numbers yet maybe someone talented in the ways of the internet could post a picture of it if they know the type I am talking about.) that has a neutral buss on each side of the panel. The main Bonding Jumper in this panel, with this design, will carry the unbalanced neutral current if any neutrals are attached to the buss on the left-hand side of the panel. This panel is widely installed in residential applications. I do not know of any clear language in the code that would prohibit the use of the main bonding jumper in this panel from being utilized in this manner.
Pete

 

[bennie]

Re: Main Bonding Jumper

Pete: This is where I thought you were going.
I don't like the term "bonding jumper",( what's new ) I don't feel it is a proper name for a bus link.

The removable link is to allow the same panel to be a service, or a feeder panel, supplied by the service.

The equipment ground conductors should terminate on the left side with the dirt rod conductor, the neutral conductors on the right side with the service multi-grounded neutral.

There is nothing wrong with mixing the wires on a service. Should this panel cease to be a service, then the wires will need sorting.

 

[don_resqcapt19]

Re: Main Bonding Jumper

Pete,
Is this a split neutral panel? If so the strap between the two neutral bars is not really a bonding jumper. It is a neutral bus. The bonding jumper would be the screw that bonds the neutral bus to the enclosure. As Bennie said, there is no problem with the mixing of the grounded and grounding conductors at the service panel. If this strap is removable, the panel could also be used as a sub-panel. In some brands the strap between the two neutral bars is not removable and the panel is listed as "suitable only for use as service equipment".

 

[pete m.]

Re: Main Bonding Jumper

This panel is set up to be used as service equipment or as a feeder panel or sub-panel. The main bonding jumper in this panel, unlike the Siemens design, when used as service equipment could and will carry neutral current. Don, you are correct that the screw is essential in bonding the neutral, but this panel also incorporates a factory provided main bonding jumper that would connect the neutral bus to the equipment enclosure via a bonding screw. If this panel were to be utilized as a sub-panel, the factory provided bonding jumper would be removed and the screw re-inserted. This would then cause the neutral buss, on the right hand side of the panel, to become isolated and the buss on the left hand side would be utilized for equipment grounding conductors since it will be the only buss bonded to the equipment enclosure. The instructions provided by the manufacturer allows neutral conductors to be connected to either buss when used as service equipment. There is a buss that runs from the left hand terminal bar to the right hand terminal bar and on the right hand terminal bar is where this main bonding jumper would be installed making a connection via the bonding screw. The service entrance grounded conductor would make its connection on the terminal on the right hand buss.(I really wish there was a picture that I could provide.)
Pete

 

[bennie]

Re: Main Bonding Jumper

Don: The bus link fits the definition of a main bonding jumper as in article 100.

The screw is only a bonding jumper as defined in article 100.

250.28 is misleading and does not match the definition as in article 100.

[ May 07, 2003, 03:46 PM: Message edited by: bennie ]

 

[pete m.]

Re: Main Bonding Jumper

If you go to the Cutler-hammer home page you can look up this loadcenter. The catalog number is ch24b200e
Pete

 

[bennie]

Re: Main Bonding Jumper

The Cutler Hammer catalog indicates this panel is...Factory bonded for service entrance applications. Remove bonding strap for separate neutral and ground bars for sub feed applications.

 

[pete m.]

Re: Main Bonding Jumper

Bennie, did you notice the main bonding jumper on the right hand side of the panel? This will act as a current carrying conductor under normal conditions if any neutral load is present on the terminal bar on the left hand side. My question: Is there a code violation here?
Pete

 

[bennie]

Re: Main Bonding Jumper

If this panel is always a service panel, I can't see anything wrong with the equipment ground conductors and neutral conductors being mixed on both sides.

 

[pete m.]

Re: Main Bonding Jumper

What about 250.6(a) and (c)? Would the current flowing on that main bonding jumper due to the neutrals be considered as objectionable? The way I am seeing 250.6(c) is that temporary currents arising from ground faults shall not be considered objectionable. One could interpret that to say that ground fault current is the only acceptable current on that main bonding jumper. Of course not withstanding the minute current flow that will always be present due to the inherent design of todays grounded electrical systems.

 

[bennie]

Re: Main Bonding Jumper

Pete: You make a good point. To be technically correct a case can be made to only place the current carrying wire on the right side with the neutral.

 

[don_resqcapt19]

Re: Main Bonding Jumper

f the bonding strap in question is connecting the two neutral bars, it is not a main bonding jumper. It is designed and intended to be a neutral bus, it will perform the function of a main bonding jumper when you land EGCs on the neutral bus, but that doesn't make it a main bonding jumper. Look at a service panel with a single neutral bar and no grounding bar. We land the EGCs on the neutral bar, but we don't call the neutral bar the "main bonding jumper". In the case with the single neutral bar the main bonding jumper is the screw that bonds the neutral bar to the panel. It is my opinion, that likewise, in the case of the split neutral, the bonding strap is a neutral bus and the main bonding jumper is the strap or screw that bonds the enclosure to the grounded conductor.
Don

 

[bennie]

Re: Main Bonding Jumper

I agree the screw is the main bonding jumper when conduit is the equipment ground conductors.

Where there is no conduit, the screw is only an enclosure bond jumper.

Cutler Hammer identifies the strap as a bond strap. Removal creates a separate ground, and neutral bus.

[ May 07, 2003, 07:00 PM: Message edited by: bennie ]

 

[pete m.]

Re: Main Bonding Jumper

Don, I also agree with you, but with this particular design the service entrance neutral will be located on the buss to the right hand side. The factory provided bonding strap will be the only connection between the neutral and the equipment enclosure. In my humble opinion this will be the Main Bonding Jumper. Now the question rears its ugly head again, is this a violation of the NEC since neutral current will flow on this connection? I personally have looked at the labeling on the loadcenter in hopes that it would require that the neutrals be located on the same buss as the service entrance neutral, but it allows the electrician to use either. Don, have you had a chance to look at the loadcenter I am talking about? If you see it, you may see where I am coming from. (then again, you may have already seen it and you are saying that I'm all wet!! )
Pete

[ May 07, 2003, 08:53 PM: Message edited by: pete m. ]

 

[don_resqcapt19]

Re: Main Bonding Jumper

Pete,
I've seen many split neutral panels, and in my opinion, the jumper between the two neutral bars is part of the grounded conductor. It is intented to carry grounded conductor current. What if you landed all of the EGCs on the bus where the service grounded conductor is landed and all of the branch circuit grounded conductors on the other bus, then what would you call this bond strap? I still say that this strap is not the main bonding jumper, but only an extension of the neutral bus that also serves as a main bonding jumper.
Don

 

[bennie]

Re: Main Bonding Jumper

A conductor that connects the equipment ground wires to the neutral is a main bonding jumper.

Connecting the equipment ground wires to the neutral bus eliminates the main bonding jumper. The green screw is then only a bond to the can.

 

[pete m.]

Re: Main Bonding Jumper

The only point that I am trying to make about this particular panel is that this piece of metal is serving two purposes; one of those being the connection of the grounded service entrance conductor to the equipment enclosure (what I would call the main bonding jumper) the second function would be to carry the unbalanced neutral current (provided of course that there would be grounded conductors on the opposing buss bar.) Take for example a Square D homeline load-center, it utilizes a "bonding screw" that only under a fault condition to the equipment enclosure or an equipment ground attached to the enclosure would it be required to carry current. The Siemens laod-center utilizes a bonding strap attached with a screw to the enclosure also, the defining difference here is that the Siemens loadcenter has a neutral buss strap that is totally independent of the Main Bonding Jumper assembly and here again the only time the Main Bonding Jumper assembly in the Siemens loadcenter will see current is the same as the conditions for the Square-D loadcenter. The Culer-Hammer design as far as I can see is unique with respect to the function of the Bonding Jumper and current flow. I can see the code issue being interpreted both ways, one seeing this as a violation and the other opinion not. I personally have inspected and approved this Loadcenter on numerous occasions, it only dawned on me that this may be a violation while attending the Ohio Chapter Western Section meeting of the IAEI on the 5th, 6th, and 7th of this month. There was some discussion on Main Bonding Jumpers and this loadcenter came to mind. Just wanted to get some other opinions.
Pete