Service ground connection

[Ken Amelin]

I saw this at an inspection yesterday.

The meter box mounted outside house with service panel directly inside basement. Main service disconnect inside panel.

I saw what looks to be a ground connection at the meter box, but there was no ground connection at the service panel??

Although I see what looks like a ground connection from the meter box to a ground rod outside, I don't see any connection from the meter box to the panel enclosure??

Is this correct?

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[Jerry Peck]

Ken,

The grounded (that bare, twisted, aluminum from the service entrance cable) is the ground and the neutral.

The a/c condenser unit outside looks like it is partially blocking access to the meter enclosure (should be off to the left to allow for the proper working space in front of the meter enclosure).

[John Dirks Jr]

Jerry,

There should be an additional grounding conductor, no? I mean in addition to the SEC neutral you mentioned.

http://www.inspectapedia.com/electric/0505s.jpg

[James Duffin]

The GEC can go to the service panel or the meter base. The neutral ties the two together.

[Ken Amelin]

The grounded (that bare, twisted, aluminum from the service entrance cable) is the ground and the neutral.

Jerry,

So if I read this correctly, are you saying that the Panel does not need an additional ground connection, as the neutral and ground are one and the same?

This is confusing.

I thought you have stated many times that the only place the neutral and ground can be connected (joined together) is at the service equipment.

I don't see the meter box as the service equipment - "No disconnect", so I thought that the panel in the basement is the service equipment??

So why is the separate ground not required at the panel?

[Jerry Peck]

I thought you have stated many times that the only place the neutral and ground can be connected (joined together) is at the service equipment.

That is correct.

The service drop (overhead) or service lateral (underground) are grounded at the transformer where the neutral conductor is grounded to earth. The service drop or service lateral has three conductors: 2 hot ungrounded conductors and 1 neutral grounded conductor. That neutral (grounded conductor) is grounded at the transformer, is ground (and neutral) from the transformer to the structure, is ground (and neutral) at the meter, and is ground (and neutral) where the service entrance conductors connect to the service equipment where the service disconnect is - to this point the ground and the neutral are one and the same.

Okay so far? The ground (and neutral) is bonded to the meter can to ground the meter can to the ground (and neutral), and the service equipment enclosure is also bonded to the ground (and neutral) ... AND ... the ground (and neutral) connects to the neutral terminal bar in the service equipment.

Still okay?

From that point on (from the service equipment on) the neutral IS NOT ALLOWED to be grounded, the neutral IS REQUIRED to be insulated from that point on, and the neutral IS REQUIRED to be isolated from ground from that point on.

In the photo, the meter can is ahead of the service equipment and there are only three conductors in there: 2 hot ungrounded conductors and 2 ground (neutral) conductor. I have been referring to that third conductor as 'ground' first to help you understand that that conductor *is* "ground" all the way to the service equipment, and it is most often not insulated either.

Thus, the first place that ground conductor becomes something 'other than ground' is at the service equipment where it becomes the neutral only (the ground is now separated from that neutral).

The result is that the neutral is only grounded at the service equipment, before that, the ground (neutral) is, well, "the ground".

Not sure if that help clear it up or if that muddied it a bit more?

Now, to add to that muddied effect, the ground is typically required to be connected at the service equipment and not at the meter can as the connection at the meter can is not open for inspection (it is behind the sealed closed cover) and most AHJ want to see that ground connection, thus they want that ground connection *in* the service equipment so they can inspect it.

Not sure if that helped clear it more or if that muddied it a bit more?

I don't see the meter box as the service equipment - "No disconnect", so I thought that the panel in the basement is the service equipment??

Correct, the meter *is not* "service equipment", but remember, that conductor is "ground" in that meter. That ground also happens to be the neutral, but in truth it is "ground".

So why is the separate ground not required at the panel?

The ground IS required to be separated "at the panel" (meaning at the "service equipment"), however, that IS "ground" going into the service equipment, and is why it is uninsulated - by the way, that uninsulated conductor going into the service equipment is also "the neutral".

Did any of that help?

[Jerry Peck]

Jerry,

There should be an additional grounding conductor, no? I mean in addition to the SEC neutral you mentioned.

http://www.inspectapedia.com/electric/0505s.jpg

John,

That is a good drawing depicting what I described in my post above, all you need to do is change one word ... where it says "the neutral wire is ... grounded at the pole", change that to read "the ground wire is ... grounded at the pole"

Think of that as a "ground" conductor, now you will see the ground from the transformer to the ground (earth ground), and that the ground runs from the transformer to the meter (which is not shown in that drawing), through the not-shown-meter to the service equipment, and that ground is tied to ground, and ... that ground is also isolated from ground at that point and becomes the "neutral" as it is no longer "ground" from that point on.

Got it?

In the case in the photos, that service equipment is simply inside the basement, not outside - oh, and there is a meter installed between the transformer and the service equipment.

[Ken Amelin]

Jerry,

So I've changed the picture and added a meter. This is what I observed at my inspection and hopefully what the photos show.

I believe I understand what you are saying - but now - If the conditions were similar and the meter was 200 ft down the driveway. Would it still be OK?? What about 500ft or 1000ft down the driveway.

AND if your answer to that is YES, then why even bother to have a second ground connection when the neutral is also grounded at the transformer???

[James Duffin]

Jerry,

So I've changed the picture and added a meter. This is what I observed at my inspection and hopefully what the photos show.

I believe I understand what you are saying - but now - If the conditions were similar and the meter was 200 ft down the driveway. Would it still be OK?? What about 500ft or 1000ft down the driveway.

AND if your answer to that is YES, then why even bother to have a second ground connection when the neutral is also grounded at the transformer???

In this scenario you would have a service disconnect at the meter and run a 4-wire feeder to the sub-panel.

[Ken Amelin]

In this scenario you would have a service disconnect at the meter and run a 4-wire feeder to the sub-panel.

James this is the same scenario as my original post? There is no separate disconnect at meter. The meter box is grounded and there is no ground connection at the panel (see pictures). Are you saying that under this scenario, I should advise my client that a separate disconnect is required at the meter and I will need a four wire feed from meter to the main service equipment panel?

The GEC can go to the service panel or the meter base. The neutral ties the two together.

Why did you originally say it was OK to be grounded at meter box? Thats the same as my sketch?

[Jerry Peck]

I believe I understand what you are saying - but now - If the conditions were similar and the meter was 200 ft down the driveway. Would it still be OK?? What about 500ft or 1000ft down the driveway.

In this scenario you would have a service disconnect at the meter and run a 4-wire feeder to the sub-panel.

James is correct, in the scenario above, with the meter "down the driveway", the service disconnect would be there, making that the service equipment, and then a 4-wire *feeder* would be run to the house, and that 4-wire wire *feeder* (not 'service entrance' cable now) would contain 2 - insulated hot ungrounded conductors; 1 - insulated neutral groundED conductor (groundED back at the service equipment down the driveway); 1 - insulated or bare groundING conductor which serves as the ground from that point on.

[Lou Romano]

If you look in any meter enclosure you will see that the neutral connection and ground are always together and incapable of being separated. So your neutral conductor from the meter to the first means of disconnect is neutral, ground and bond.

In the panel (or wherever the first means of disconnect is located) there should be either a bonding screw installed through the neutral bar to the panel box or a bonding jumper installed from the neutral bar to the panel box. This grounds the panel and and bonds the metal parts of the electrical system.

The neutral must be bonded to ground at the first means of disconnect. This is the only place you are allowed to bond the neutral to ground!

If you were to run a separate ground from the meter you would be paralleling the neutral.

[Bill Kriegh]

Way too much changing things around to try and simplify. The (sometimes) bare wire from the transformer center tap to the center lug in the meter housing is a neutral. It is derived directly from the center point of the secondary winding of the transformer. And, if the neutral wasn't grounded at the transformer or at the meter things would (and do, in some cases) work just fine. Taken another way, the ground IS NOT necessary for the electrical system to function. We have, in this country, simply elected to ground one of the electrical conductors for several beneficial reasons.

You need to understand that the grounding electrode is there to assist in preventing the electrical potential between the ground and electrical equipment from becoming significant. This matters if, for example, a high voltage wire is damaged and falls on to the lower voltage wiring that supplies a house. The electrode provides the path to ground you would otherwise be if the ground wasn't present and you came in contact with the equipment housings or metallic conduit. This connection is not intended to be a current path. But, since electricity tends to use all available paths back to the source there is negligible current that flows between the grounding electrode and the transformer ground connection.

The neutral is bonded to the meter housing internally, with the terminals being mounted directly on the meter housing inside. From there, the neutral runs to the service disconnect housing. For the distance this wire runs between the meter housing and the disconnect it serves the functions of both neutral and grounding electrode conductor (GEC). So, it doesn't matter whether whether the GEC is attached at the meter or service disconnect, it is simply on one end or the other of the same wire at this point. This shouldn't be happening anywhere else in the system.

Most utilities don't want anything in the meter housing but the service wiring and the default location for the grounding electrode connection becomes the disconnect. There are exceptions for everything, and some localities have rules that require the grounding electrode be in the meter housing.

FWIW, the above describes a "hot sequence" metering system, meaning that the disconnect is after the meter. Rules change a bit for a "cold sequence" arrangement where the disconnect is prior to the meter - typically a commercial and/or industrial arrangement.

Grounding is a complex issue. If you are going to concern yourself with the "hows and whys" then a good book on grounding is in order.

[Ken Amelin]

Everyone,

Thanks for your input. It was most helpful and answered most of my questions.

Grounding, grounded, ground - all very confusing but interesting. I think I'll take Bill's advice and read a book on "grounding".

You'll know if I learned anything when you start to see me answering other peoples questions.