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Old 09-26-2008, 11:57 PM   #1
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Adding ground bar to main panel


I'm in the process of planning a sub-panel addition to my basement workshop since my main 200 amp panel is maxed out with circuits. I will be moving an existing 240 volt 20 amp circuit to the sub-panel to free up space for a 60 amp feeder breaker. So far so good.

When I opened the existing main panel to check out what I'd be dealing with, I notice that my builder had added a few circuits (using half-width breakers) about 19 years ago during a basement finishing project he did for me shortly after my house was built. Since there were not enough existing connection points on the grounded / grounding bus bars (one on each side, tied together), he placed two grounded conductors (white wires) together within one terminal space. (He did this at two locations on the bus bar). This is an obvious code violation, since the white wires should each have their own terminal connection.

In addition, I notice that he mixed the grounded conductors (white wires) and the equipment grounding conductors (bare wires) on both bus bars. This may not be a big deal, since they should be bonded together anyway in the main service panel. It's just that every picture I've seen of main service panels show the white wires all going to one bus bar and the bare grounding wires going to a different bus bar, with the two bus bars bonded together.

Now for my questions:

1. Is it alright to add another grounding bus bar to the main service panel 2 inches adjacent to one of the existing bus bars? I would have to drill a hole through the back of the panel to mount the bus bar since the Siemens panel I have does not seem to prepped for it. I could then move several of the existing bare grounding wires over to the new bus bar and free up spaces on the original bus bar so that each grounded conductor (white wire) can have its own terminal. I would directly connect the new bus bar with the adjacent one using 10 awg wire. My alternative is to move these added-on circuits over to my new sub-panel. This would be more work and expense.

2. Is it considered good practice to separate the white and bare wires onto different bus bars in the main service panel, or is my mixed arrangement commonly seen? I know I have to keep them separate in the sub-panel, since they cannot be bonded. I just wondered what "standard" practice was for the main service panel.

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Old 09-27-2008, 12:49 AM   #2
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Adding ground bar to main panel


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1. Is it alright to add another grounding bus bar to the main service panel 2 inches adjacent to one of the existing bus bars? I would have to drill a hole through the back of the panel to mount the bus bar since the Siemens panel I have does not seem to prepped for it. I could then move several of the existing bare grounding wires over to the new bus bar and free up spaces on the original bus bar so that each grounded conductor (white wire) can have its own terminal. I would directly connect the new bus bar with the adjacent one using 10 awg wire. My alternative is to move these added-on circuits over to my new sub-panel. This would be more work and expense.
No, you shouldn't be drilling and tapping new holes in the panel jacket. It would be a technical violation of the panel's listing and is therefore not permitted. You can usually buy a longer ground bar though that will match up to the holes that the current bar is mounted to.

2. Is it considered good practice to separate the white and bare wires onto different bus bars in the main service panel, or is my mixed arrangement commonly seen? I know I have to keep them separate in the sub-panel, since they cannot be bonded. I just wondered what "standard" practice was for the main service panel.
Provided that the main service disconnect occurs at this panel, you can mix grounded conductors (white) and grounding conductors (bare) on the same bar. It is just fine. They just can't occupy the same slot, and as you said, you can't land multiple neutrals in the same lug. Multiple grounds of the same wire gauge are typically ok...The panel's sticker will give the allowable quantities per lug (usually 2 or 3). Consolidating some grounds together might also buy you the extra space you need in the bar.

On a sub-panel, the neutrals and grounds are not bonded together.

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Old 09-27-2008, 10:41 AM   #3
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Adding ground bar to main panel


As KC mentioned, you have to do what the manufacturer says you can do. Drilling and tapping most likely is not going to be in any of their listed instructions. If available, longer grounding bars listed for use with that panel is what you should look for.

The practice of using one bar for neutrals and the other for grounds makes for a clean looking installation. Other than that, serves no real purpose.

There is a reason though that neutrals can only terminate by themselves. If you were to loose the neutral connection at the panel of a properly connected multi-wire branch circuit, that circuit instantly becomes a 240V circuit. Thus if you were to remove a neutral of a MWBC while removing another wire under the same screw...well, you get the idea.

Personally on a new build install, I like to have the neutrals on the upper half (or so) of the bar and their grounds on the lower half of the same bar. Makes them easier to find and pull out if necessary. Remodels and upgrades rarely give that luxury though.
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Old 09-27-2008, 11:09 AM   #4
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Adding ground bar to main panel


Agreed. Personally, I land my grounds and neutrals on separate bars when I do new panels and can get away with it...That's just for clean looks though, and isn't driven by any safety or code-based requirement (unless it's a subpanel).
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Old 09-27-2008, 12:24 PM   #5
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Adding ground bar to main panel


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No, you shouldn't be drilling and tapping new holes in the panel jacket. It would be a technical violation of the panel's listing and is therefore not permitted.
I'd like to see the documentation showing it's a violation of the listing.

Panelboards are drilled/tapped all day long with no issues from the inspectors. Except for very thin enclosures I've never had a problem tapping a panel, the metal is almost always thick enough. Siemens is no exception.

2008 NEC 250.8(A)5 says that as long as machine screws engage the sheetmetal at least 2 threads or are secured with a nut, it is okay.

By your logic, if I turn an existing obsolete panelboard into a subpanel and need to isolate neutrals/grounds with no factory ground bar(newer grd bars most likely don't line up to the existing panels factory holes) I would have to replace the panel because I can't drill/tap it. That's ridiculous.
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Old 09-27-2008, 01:44 PM   #6
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Adding ground bar to main panel


So we disagree a little bit.
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I'd like to see the documentation showing it's a violation of the listing.
Look no farther than the panelboard's listing. If you make modifications to it that are not permitted by its particular listing, you've violated the listing of a tested/listed device, fixture, or appliance...That's a violation of code. My NEC's at work, so can't give you a code section just yet.

Practicality dictates that there's very little real-world hazard with drilling and tapping in a new ground or neutral bar, and brand name doesn't matter. But if you think you can take one manufacturer's bar listed for use in their panel and fit/install it in another manufacturer's panel...And not violate the listing, you're wrong.

That's ridiculous.
And that's not very nice of you Cow. If you would like to prove me wrong with a Siemens listing, feel free. Some manufacturers may allow it, some do not.
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Old 09-27-2008, 04:52 PM   #7
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Adding ground bar to main panel


Most manufacturers of residential load centers have specific documentation in there technical libraries that will give instructions on how to ad ground bars to the panel back plate. This is usually only needed in panels that were intended to be used only as service equipment. The addition of a 'neutral' bar to which you intend to terminate neutrals and grounded legs is not allowed to be in contact with the metal of the enclosure if a neutral bar already exists in the panel.

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