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Bonding the grounding lug to neutral


Marc
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Yesterday's inspection had a typical main panel with what looked like a vertical neutral bar on each side. But in fact, the incoming neutral bar connects solidly only to the neutral bar on the left side. The right side bar is connected only via two green grounding screws (one on each bar) and the enclosure itself. There are no neutral conductors connected to the right bar, just a few equipment grounding conductors.

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The question is this: Isn't an equipment grounding busbar supposed to be solidly connected to the neutral conductor in a main panel? I can't find it in the 08' NEC.

Marc

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Yesterday's inspection had a typical main panel with what looked like a vertical neutral bar on each side. But in fact, the incoming neutral bar connects solidly only to the neutral bar on the left side. The right side bar is connected only via two green grounding screws (one on each bar) and the enclosure itself. There are no neutral conductors connected to the right bar, just a few equipment grounding conductors.

The question is this: Isn't an equipment grounding busbar supposed to be solidly connected to the neutral conductor in a main panel? I can't find it in the 08' NEC.

Try 250.24(B). It says what you're saying.

But also look in 250.28(A) & (B), where it says that the bonding jumper can be a green screw.

- Jim Katen, Oregon

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That right side bus is functioning as a service grounding bus. You can see the service grounding conductor attached at the upper right disappearing out through the upper right side of the enclosure.

The green screws are not "grounding" screws, they are bonding screws. If that were a sub-panel, the bond screw would be left out of the left bus, to isolate the neutral bus from the enclosure, and all grounded (neutral) conductors would be on the left bus. The green bonding screw would still be installed in the right bus to ensure that the enclosure was grounded and all equipment grounding conductors would end on that right bus. When it's a service entrance panel, the the grounded conductors and the equipment grounding conductors don't need to be isolated and the two green bonding screws allow the enclosure the function the same way that a tie bar normally functions.

ONE TEAM - ONE FIGHT!!!

Mike

(Dang, just posted and saw that Katen beat me to it with, of course, a far simple explanation than my rambling.)

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That right side bus is functioning as a service grounding bus. You can see the service grounding conductor attached at the upper right disappearing out through the upper right side of the enclosure.

The green screws are not "grounding" screws, they are bonding screws. If that were a sub-panel, the bond screw would be left out of the left bus, to isolate the neutral bus from the enclosure, and all grounded (neutral) conductors would be on the left bus. The green bonding screw would still be installed in the right bus to ensure that the enclosure was grounded and all equipment grounding conductors would end on that right bus. When it's a service entrance panel, the the grounded conductors and the equipment grounding conductors don't need to be isolated and the two green bonding screws allow the enclosure the function the same way that a tie bar normally functions.

ONE TEAM - ONE FIGHT!!!

Mike

(Dang, just posted and saw that Katen beat me to it with, of course, a far simple explanation than my rambling.)

That's the whole point here. The two green bonding screws along with the enclosure should NOT be used as a tie bar, even for an equipment grounding bus. The usual tie bar that we are accustomed to seeing isn't installed on this particular panel. At least I cannot see any evidence of it.

Jim's suggestion [250.28 (A)] seems to be what I need i.e. panel enclosure cannot be used to form the connection between the equipment grounding bus and neutral bus. Agree?

Marc

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. . . Jim's suggestion [250.28 (A)] seems to be what I need i.e. panel enclosure cannot be used to form the connection between the equipment grounding bus and neutral bus. Agree?

No, because 250.28 allows the screws. Now this is for *equipment grounding conductors*.

You might be thinking of the prohibition against using the screws for the *grounding electrode conductor*. That rule is in 250.24(A)(1).

FWIW, I think that's what's wrong with the panel in your picture. At the upper right side, it looks like the solid #6 copper wire is the grounding electrode conductor. It should have been run to the empty lug at the upper left side, next to the incoming neutral. The little green screws aren't supposed to be part of the grounding electrode system. However, they're fine for regular branch circuit equipment grounding conductors.

- Jim Katen, Oregon

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In those areas where you can use the nylon jacketed SEC, is there any bond to the meter socket or other equipment?

How do you do that?

Here, it's all hard pipe, with bonding cables and clamps on everything.

In that case, we bond the meter can to the service neutral at the meter can. Then we bond the service panel again. The service neutral acts as the bonding connection. Since the meter occurs before the service panel, we can do that. We can't use the neutral for bonding *after* the service disconnect.

- Jim Katen, Oregon

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Do you have a make, model and manufacture of the panel Marc? I tried to save the pic to desktop and zoom in but the file is to small.

Is there a chance the bonding jumper is molded in somewhere unseen?

No, I don't Terry. The original photo is only 0.3 MP. I guess there could be a jumper installed somewhere between the two bars but I couldn't see it.

Chad has a point, maybe this isn't a main panel, but a sub panel. If so, it's built a little differently. I can't even confirm now that the 100Amp breaker at the top is rated for use as a service disconnect.

Marc

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FWIW, I think that's what's wrong with the panel in your picture. At the upper right side, it looks like the solid #6 copper wire is the grounding electrode conductor. It should have been run to the empty lug at the upper left side, next to the incoming neutral. The little green screws aren't supposed to be part of the grounding electrode system. However, they're fine for regular branch circuit equipment grounding conductors.

- Jim Katen, Oregon

It is the GEC. I hadn't noticed that mistake until now.

All posts much appreciated.

Marc

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I understand what those citations say, but in the real world moving that GEC changes very little. What's the thinking there?

It changes the impedance of the grounding electrode system.

Remember that the equipment grounding conductors and the grounding electrode conductors serve two completely different & unrelated functions. The equipment grounding conductor are there to carry fault current back to the panel and cause a breaker to trip. You don't need a particularly low-impedance path for that. Any old conductive thing will do.

On the other hand, the grounding electrode conductor has nothing to do with clearing faults. It's there to deal with surges. Sometimes very large & very sudden ones. For that, you really want as little resistance in the electrical path as you can get. That's one of the reasons why splices aren't allowed in the grounding electrode conductor and its the reason why it's not supposed to rely on the little green screws.

- Jim Katen, Oregon

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FWIW, I think that's what's wrong with the panel in your picture. At the upper right side, it looks like the solid #6 copper wire is the grounding electrode conductor. It should have been run to the empty lug at the upper left side, next to the incoming neutral. The little green screws aren't supposed to be part of the grounding electrode system. However, they're fine for regular branch circuit equipment grounding conductors.

- Jim Katen, Oregon

It is the GEC. I hadn't noticed that mistake until now.

All posts much appreciated.

Marc

Also I forgot to mention (though you probably know this) that an alternative fix would simply be to run a jumper wire from one terminal to the other.

- Jim Katen, Oregon

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