I'm installing an extra ground bar into a 200A Cutler Hammer panel. There are no threaded holes to attached the ground bar. Does anybody know if: 1) Can use a screw and attach the bar by screwing through the panel and into the wood behind the panel. 2) Do I have to use a Cutler Hammer Buss bar, or will any manufacturer work. 3)Is there a requirement to have an insulator behind the ground buss bar? Thanks - KD

1) A screw going into the wood behind the panel is incorrect. You can drill and tap the correct holes in the panel tub and use the screws that came with the bus bar.
2) The CH bus bar is probably the only one listed for use in that panel. Even the big orange store has them.
3)Nope, that's just for neutrals or IG's

If there is a field drilled and tapped hole for a grounding bus I would want to see a #4 jumper wire to the main bus where the grounded conductor from the service resides.
The "factory" holes are usually formed with a bubble of extra metal that allows a couple of threads to bite. You will only get one good thread with a tapped hole in most cabinets and I doubt that is sufficient. It certainly isn't "listed" that way.
I personally am not a big fan of the "screw" MBJ in the first place but I would certainly want to see it in the factory hole it was tested with.

I would just get the kit,the bar,drill bit and fine thead self tapping screws come in a little sealed bag.If you order just the bar (usually 10' lengths) ask for a bag of screws.You can put a tap into the cordless drill and run through the holes also.Ive never seen insulators used unless it's an isolated ground system.Wood screws or anything with a course thread makes a bad electrical connection and passing a screw into the wall may jack the holes in the panel.You must have good electrical connection to the panel or you compromise all circuit grounds that you terminate to this grounding bar.Make sure the proper screws are used so the just get the kit.

It should be clear that "sheet-metal" type self-tapping screws are a NO-GO, and violate 250.8. Like wise on the use of "Wood Screw"! You could post a picture of that in violations forum.

If this is a newer cut-ham panel, it will have 2 sets of the holes intended for this use, 1 on each side. And the applicable listed ground bar will be listed on the door lable.

If not available, most inspectors will accept a like-in-kind installtion. Using parts "listed for the purpose", like a simular ground bar with (2) 10/32 threaded screws that come with it.

gfretwell, I don't think a #4 to the main is nessesary. You'd have to find a code for that one to not twist my arm for that. Although it does the job, and does it well, it's over-kill. Conduit, cable or sized for the feeder, OK, #6 max to feeder source.

BTW, the one of very few panels that have that extra thick or deep sleeve for ground screws is SqD. Cut-ham and murray are tin-can thin these days.

I will have to disagree with e57, but not for the reasons you might expect. As I see, you can mount any bar, any way you like...but you cannot rely upon the metal of the case for bonding the new bar to the old one. I believe that you are required to connect the two with a jumper no smaller than #8.

I just like the jumper as opposed to depending on a tapped hole, field cut to be both the attaching and bonding screw.

I only said #4 since you probably have a scrap left over from the main bonding jumper.
I agree #8 would be fine. I would trust a foot of #12 to operate any branch circuit O/C device you are likely to have but why not use the biggest wire in your scrap bag that fits the lug?

I agree with Mark (e57). There is no need to install a bonding jumper between multiple grounding bars. Why wouldn’t the box be a sufficient connection between the bars? If all metal raceways are use the box is sufficient to bond all the raceways together.

Curt

Curt, I would agree if the "listed" bar was attached in the factory tapped holes with the screw supplied. (per manufacturer's instructions)

THAT is what was tested and approved. Anything else would kick me back to a 250.66 sized main bonding jumper.

Every ground bar I have purchased came with screws and directions for drilling, tapping, and mounting in "non-factory" holes.

The "dimple" created by the panel manufacturer does not change the thickness of the metal therefore it cannot change or increase the number of threads formed by tapping a "flat" surface.

Minor point but, most ground bars are not UL Listed, rather they are Recognized as components which means they are intended (must be) to be mounted into something.

I guess it all comes down to how you read 110.3(B) and the label in the panel.

If it takes a little extra time to make the any installation better or safer why not?Inspection has never requested or ordered that i install a the jumper but it is logical code or not.The code is just the bare minimum required by law.Good call gfretwell.

If you need more grounding terminals how about replacing the exsisting ground bar with a longer one that has more terminal screws?

Blessings.

Mark

Use existing holes, drill and tap, whatever. No need for a jumper.

Not long ago I had a similar problem with an old exterior main. Factory ground bar and no exra mounting screw holes( they didn't need them a few years ago). I choose the bonding jumper option ( solid #4). Since your not trying to bond the panel it doesn't matter about mounting hardware( can tap holes ). The rule on not using sheet metal screws is to keep people from using them to bond the panel, if they loosen, you would not have a good mechanical connection.I agree with gfretwell. I have seen loose ground bars in panels with factory screws.I think there should be a nice big factory welded lug there for bonding. I have this fear of grabing a live panel cover. allways touch with the back of my hand first.

Seems to me that the machine thread screw is there to bond the panel enclosure. I don't think that screw would be rated to carry a fault from say a 50 amp range. Seems the screw would burn up if it were trying to carry that load to ground. I agree it should have a jumper wire from a lug on the original ground bar to a lug on the second ground bar.

I noticed that the original poster never responded, but I took the question to mean that he's installing a grounding bar to separate the grounds and neutrals, as in a sub-panel.

If this is correct, then naturally, the jumper mentioned first by GF would be contra-indicated.

As an aside, in most cases, a 1/4x20 screw is used to bond a breaker cabinet, and would most certainly be capable of carrying a 50-amp fault current.

Why not just bolt and nut an extra ground bar to the side of the panel. That would work just as well as the factory and don't forget to remove the paint for a good connection.

Harold, the reason I see this a a situation requiring a bonding jumper is that I don't see the steel case as mich of a cunductor at all. Why, even if the case were made of copper, how much of a cross section is there (think diameter of screw x thickness of case). What is that equal to? 10 gage wire? I see the screws bonding the case to the bar, and not the other way around. I'd bond the bars together with a piece of #8 wire. Just to be sure.

For you guys that feel a bonding jumper is neccesary, why would not on manufacturer or the NEC require it? Because it is not needed.

Scott, I understand your position...the box is bonded, and conducts, so there's the electrical continuity you need....and why should we ask more of this connection than we ask of every coupling in the conduit? I will also admit that I am completely unaware of any bad things happening as a result of using the mounting screws as your bond.

Here is where I find the requirement....you are required to have a bond sufficient for anticipated overcurrents, so as to clear a fault (as the code explains). With a ground bar, you need a bond ing connection able to carry everything that bar can- and with multiple circuits, I question the capacity of the screw connections. The code constantly refers us to table 250.66- and the smallest wire listed is #8 copper. Finally, in 250.92(B) the code discusses "bonding at the service."

250.92(B) lista any number of permitted methods of bonding, but using the monting screws isn't one of them. The closest suggested way is #4, which suggests 'bushings with bonding jumpers.'


Another point that has influenced my thinking was demonstrated when I wired an audio recording studio. There I learned that even properly made-up pipe produces some radio static from tiny amounts of arcing at every connection. To reduce this electronic noise, ground wires were run to isolated devices. (The conduit then acted as a "shield" for the ground wires). In using such a jumper, I am trying to reduce the current that will flow through the mounting connections.

Is it overkill? Probably. Does Code require such a jumper? I think so. Has anyone ever been cited? I doubt it.

And, as to the "Panel or sub-panel" issue, I am only speaking of bonding one ground bar to the original ground bar. The connection to the "neutral" system hasn't been changed at all.

Everyone seems to take it for granted that this a service.
The original question referred only to a 200 Amp Panel.
Here's a pic of a Cutler Hammer ground bar, properly installed in a 200 amp panel with no jumper.



I've got no objection to putting a jumper on of course, but I wouldn't have any objection to putting grounding bushings on every conduit in the building, either, as long as someone else was doing it.

It is funny how some topics really can get peoples "dander" up

If the enclosure for a service or a subpanel does not have the threaded holes for a "KIT" that can be mounted via the installation instructions, than the bus/bar that is mounted by an installer without these provisions has not been tested as effective, and will require bonding to the original bus in the enclosure.

250.130(A), 250.24(B) and the UL Directory that also has specific language on this topic.

I know that we all know this is the most important connection that we make everyday - the effective ground fault current path!!!