Thread: Metal Nipple for ground

Yesterday I inspected this home with an older type main service disconnect box (not able to open it - would have to shut off main switch interlock) that fed an adjacent panel. A metal nipple was used to bond the panel. I'm not sure if that disconnect box was just a switch or if it was also fused. You can also see that the disconnect switch is rated for 200A, but the adjacent panel, main breaker, and wire size are rated for 100A.

As seen in the picture, there is not a separate neutral and ground bar or a separate ground wire to the adjacent 100A distribution panel. I will be writing it up as such. I started thinking though and wondered if that metal nipple (close coupled) connection would classify the adjacent panel as part of the main service equipment?

You can see the ground wire coming out the bottom of the old main disconnect, so I considered the switch the service equipment and not the adjacent panel.

Does the adjacent panel require a four wire connection with separate ground and neutral bars or does the metal nipple make this panel part of the service equipment?

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Originally Posted by Ken Amelin

Yesterday I inspected this home with an older type main service disconnect box ...

Let's stop right there at what that is: "main service disconnect".

Where is the neutral bonded to ground, and only where is the neutral allowed to be bonded to ground?

From that point on (an obvious follow-up to the above) the neutral is required to be isolated from ground.

I believe you will find your answer to what is required to feed the panel from the service equipment in the above and whether or not the neutrals and grounds are allowed to be on the same terminal bar in that panel.

The nipple in your picture can be used as the grounding conductor but the grounded conductor should not be connected in any way to the grounding conductor after leaving the service eqipment. The picture shows a bonding screw that should be removed seperating the grounding conductor from the grounded conductor and if any grounding conductors are on the grounded bar they should also be removed. That is a square D panel and the grounding bars would be located on both sides of the panel under all the ungrounded conductors so I cannot tell if they are present and being used but I do not see any grounding conductors on the grounded bar with the picture shown so I would have to believe they are present.

from tho 06 IRC

E3808.8 Types of equipment grounding conductors.

The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:


1. A copper, aluminum or copper-clad conductor. This conductor shall be solid or stranded; insulated, covered or bare; and in the form of a wire or a busbar of any shape.
2. Rigid metal conduit.
3. Intermediate metal conduit.
4. Electrical metallic tubing.
5. Armor of Type AC cable in accordance with Section E3808.4.
6. The combined metallic sheath and grounding conductor of interlocked metal tape-type MC cable where listed and identified for grounding.
7. The metallic sheath or the combined metallic sheath and grounding conductors of the smooth or corrugated tube type MC cable where listed and identified for grounding.
8. Other electrically continuous metal raceways and auxiliary gutters.
9. Surface metal raceways listed for grounding.


























t

Hard to tell from the description if the original disco is even being used anymore. Perhaps someone ran the unfused conductors thru the old box as a raceway and there is no connection with the current service.

Originally Posted by Jim Port

Perhaps someone ran the unfused conductors thru the old box as a raceway and there is no connection with the current service.

Good thought, Jim. That panel to the right does have a main disconnect in it, so you might be right there - I never thought about that possibility.

But one needs to stress "perhaps" and "possibility" and not presume that is the case, as such a recommendation would be in order to have the electrical contractor very what is in the original service equipment and if it is still being used as anything other than a gutted "wire way" or "junction box".