Here's the situation- The contractor tapped the 400a residential meter can twice with Service Entrance conductors. Once with 4/0 Aluminum to feed a 200a Service panel and again with 2/0 Aluminum to feed a 150a Service panel. Then he installed a #4 awg cu. GEC out of the 200a Service panel and ran it to the water service. Out of the 150a Service panel he ran a GEC #6 awg cu to the water service. The water service is about 75 feet from the Electrical Service panels. What is wrong with this approach?

250.66 table says "Size of Largest Ungrounded Service-Entrance Conductor".

Then you read note 1 and it says

"Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set."

so it sounds more like you can have one GEC, but you size it to the sum of the 2/0 and the 4/0 (344Kcmil) rounded up to 350 which gives you a #2 copper GEC to the first electrode which could be tapped by the #4 and #6 going to each panel.

From a practical sense I am not sure what difference it makes.

George, the problem is the neutral conductors to each panel are in a parallel loop with thes two GEC's.

Roger

Roger- I'm not sure I understand your statment about paralleled conductors if I take the purist difinition of paralled conductors as discribed in Article 300. As for Greg's statment, I agree with his calculation approach and that's the way I teach it. I like the illustration in the handbook (I know, I know) because it's clear and cost effective if your trying to save the customer money. Typically, I would see a number 2 coming out of the 200a panel going to the water service and a number 6 coming out of the 150a panel and being split bolted on to the number 2 external to the 200a panel right there at the electrical service location.

Exhibit 250.28 is the paradox. If he put a 6" piece of #2 on the water pipe and tapped that for each panel it would look like the picture in the handbook but I would see that as a spliced GEC. (obviously I don't like exhibit 250.28)

The most elegant solution is to make the GEC connection in the meter base with a #2 but that is not what he did.

I do see the "loop" Roger is talking about but that exists in exhibit 250.28 too. I think one #2 in either service panel would satisfy 250.24(A)(1)

Hello George and Greg, this is what I'm seeing.



IMO the GEC should be a single point connection sized for a single service.


Roger

If you think about it, in places where landing the GEC in the meter is not allowed (because it's inaccessible due to the meter tag), there is no way to avoid paralleling the neutral with GEC's with multiple disconnects/panels.

In fact, with metallic service-cable conduits, the conduit itself always parallels the neutral. I wish we could use the meter's lug for the GEC, since it's already outside.

George,
It would pass inspection.
Only thing "wrong" would possible be cost and minor waste of copper.
It is an alternative way of doing things.
Multiple services can use a single large GEC with permanent taps to the other services OR each can have a GEC sized for that service*.
As far as parallel pathes, having more than one Grounding electrode bonded together would mean parallel pathes,but only to ground (earth). [two rods six ft. apart]
Not a violation.
Alan--
*I have seen six GEC connected to the same ground rod, with seperate clamps, for a six unit apt. blding. Waste of copper in my opinion.
***Make sure he labels the service disconnects 1 of 2 & 2 of 2 NEC 230.70(B)



[This message has been edited by Alan Nadon (edited 11-29-2005).]

Just read 250.64(D) and I don't see a problem with doing it that way and what I noted is that the GEC "tap" conductors must extend inside the panels involved. So coming off the meter base don't solve the problem that Roger stated about parallel conductors. I'm still struggling with the fact that we are having a parallel situation here. I don't think it is a true parallel condition. We do have conductors that are both returning to the Xformer but the GEC is really just a back-up for the Neutral but even if we, for one fleeting moment, considered them in parallel the different sizes would violate 310.4. If the code considered them to be in parallel then I'd expect them to comply with 310.4.

They get pretty serious about the parallel neutral deal here. If the GEC lands in the meter can there can't be a parallel path to the service disconnect enclosure (3 wire SEC in PVC is the norm).
On the line side of the GEC they don't seem to care since there is always some sort of parallel path, even if it is just through the dirt. I will usually see about 2-3a on my GEC and I saw similar currents on the #8cu that comes down the poles from the transformers around the neighborhood. Yeah I know, I have too much time on my hands.

I am still not sure why he couldn't ground the service in one of the disconnects with a #2 and be done with it.

gfretwell wrote: I am still not sure why he couldn't ground the service in one of the disconnects with a #2 and be done with it.

That's exactly what he should do. As long as the neutral is sized equal to or above the 250.66 size, it can ground either or both panels. Just because you are permitted to run GEC taps doesn't mean you have to.

Also, what size service entrance conductors were run on the line side of the meter? Need to make sure that a #2 is large enough by examining all of the SE conductors.

Here is a quote from Soares based on your described installation...

"If the installer chooses to, an individual grounding electrode conductor may be installed from each service disconnecting means enclosure to the grounding electrode.

In this case the GEC is sized for the service-entrance conductor serving that enclosure.

The code does not specifically address or prohibit this concept but it is similar to connecting taps to a common grounding electrode conductor. In this case the taps are connected directly to the electrode."

shortcircuit

Mark- There are no Service Entrance conductors on the line side of the meter. There is an underground lateral coming from the utility company to the meter and the utility company will not permit the GEC to orginate in their meter. I appreciate the reference to Soares and I guess since we have two service panels we are dealing with coming out of each panel with a properly sized GEC to the electrode system. As Greg indicated a person could use Note #1 of T. 250.66 and then based on the "Tap" rules come out of the other panel with a properly sized tap conductor and save the cost of installing two conductors all the way to the electrode.

"no Service Entrance conductors on the line side of the meter. There is an underground lateral coming from the utility company"

"underground lateral from the utility company" = "Service Entrance conductors"

And the GEC needs to be sized for them...

Anyway... I think its clear the code wants one GEC per lateral. Although Soares opinion might differ.... (What if one service is removed, and you have a just a #6 covering the grounding for 350MCM SE conductors?)

Commentary from 230.40 exception 2... "Note that in such cases the lateral conductors are considered [i]one service lateral."

Also, how can anyone do a complete job without knowing what the meter is fed with, (Not opening the meter) otherwise you would never know what size the GEC should be.

IMO the GEC crimps or welds should be right below the equipment. Or run a single conductor in and out of both panels. The allowing of taps seems to be making it easier for you... "the tap method eliminates the difficulties found in looping grounding electrode conductors from one enclosure to another." (From the commentary following 250.64(D) )

I think someone should read in Article 100 about the definition of "Service Entrance Conductors" - They are Not the lateral. And if your going to copy and paste from the NEC you might want to check the copyright permissions.

George:

Please look at this:
https://www.electrical-contractor.net/ubb/Forum1/HTML/006592.html

That should ally your concerns over quoting Code in the forums.

Thanks for the link and information on copy and paste. I was and still am not real comfortable with copying and pasteing but I feel better now and that's what this forum is all about. That said, I found some very enlightening information in Soares Grounding that covers the subject of this thread. Check out p.118 of Soares Grounding 8th edition. It appears that coming out of muliple Service panel and running to the Grounding Electrode with a GEC is one of many ways of complying with the NEC.

What I am curious about is whether the lugs in the meter enclosure are UL listed for more than one conductor???

George, "Service Entrance Conductors" can be pretty broad. (Depending on where you are...) Here, where I am, it is entrance to, or attachment to the building. Most service equipment and metering (customer owned) are inside... In terms of the definitions from the NEC, take a look at "Service Lateral", and "Service Point", both help determine where "Service Entrance Conductors" begin.

Anyway, my point was that what you have is two GEC's, and two connections to the water are a splice in what is supposed to be one conductor. (If you are inspecting to the NEC, not Soares...)

The code specifically permits the GEC to run from one electrode to another.
I cannot see how two GECs that are terminated on the same electrode would be a spliced GEC violation just because they both originated in the same vicinity. By that logic the separate service permitted for fire pumps could not be grounded to the electrodes that are used for the main service. In fact any failure to use the same electrodes for a separate service would be a violation of
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison

I wouldn't call it a splice either, but I think there may be some other issues. If each (or just one) wire from the panel to the pipe is sized per 250.66, then I see no problem. However, if these are GEC taps and a full size GEC was not run to the pipe, then I don't know if that meets the requirements of 250.64(D).

I see that the first 5' of a pipe can be an electrode, and used to bond other electrodes, but can that pipe be the full sized GEC itself and small taps from from it to panels?

Personally, I don't see why it can't be done this way, but I'm not sure this is permissible based on the definition of GEC. But running a short stub of #2 or 1/0 from that pipe and split bolting taps to it seems like a worse implementation.

George:

First question I have is when did the utility start supplying a 400 Ampere meter enclosure? Second, are the lugs in the meter enclosure rated for more than 1 conductor? Based on the reply to these questions I think that the bonding requirements of 250-66 should be based on the 400 Ampere service as supplied by the utility. Expand on this and imagine 6 main breaker panels and a fire pump installed on this service. Knowing you I surely would not want to be the inspection after that one.

Paul, What most sparkys call a 400A meterbase is what the PoCo calls a 320A self-contained meter base. They are usually provided with studs for mounting double barrel lugs to feed (2) 200A loadcenters w parrallel 2/0 CU or 4/0 AL but I have seen them with single 600kcmil lugs and 500kcmil CU feeding a 400A disconnect. 320A (80% of 400A)continuous is what the PoCo calls this single phase metering set-up and usually sets this size as the maximum for self-contained metering. Anything larger is usually current transformer metered.

Paul, Landis & Gyr makes a 320-amp continuous meter socket with single barrel lugs that are listed for 2 conductors.

Paul- Fred pretty well covered it. Our utility company here is SE Michigan show the 400a can in the "Green Book" and it's for residential underground only (some exceptions). As for a fire pump, well, I've only been involved with one of them in residential. It was a group home and we taped ahead of the service panel for it.