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Joined: May 2005
Posts: 1
Junior Member
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

Joined: Oct 2004
Posts: 132
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

Joined: Jul 2004
Posts: 9,942
Likes: 34
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.

Greg Fretwell
Joined: May 2001
Posts: 378
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.

Joined: May 2003
Posts: 2,876
e57 Offline
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.

Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: Jan 2005
Posts: 5,445
Likes: 3
Cat Servant
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.

Joined: Jul 2004
Posts: 9,942
Likes: 34
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?

Greg Fretwell
Joined: Apr 2002
Posts: 558
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 Swartz
Joined: Jul 2004
Posts: 9,942
Likes: 34
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.

Greg Fretwell
Joined: Jul 2001
Posts: 599
JBD Offline
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.

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