Bonding meter can

[iwire]

Re: Bonding meter can

Originally posted by roger:
Hello Bob,

Originally posted by iwire:

It does seem counter productive to run the lightning current into the building only to try to send it back out of the building.

Roger

Hi Roger

When looking at it from this point of veiw it seems like the GEC should run from the weather head straight down the outside of the structure to a ground electrode right there in the ground, then inside to any other electrodes.

Bob

 

[roger]

Re: Bonding meter can

Bob,

When looking at it from this point of veiw it seems like the GEC should run from the weather head straight down the outside of the structure to a ground electrode right there in the ground, then inside to any other electrodes.

I have actually heard of it being done that way, and also think it would be the best idea.

Roger

 

[peter d]

Re: Bonding meter can

Originally posted by iwire:
Hi Roger

When looking at it from this point of veiw it seems like the GEC should run from the weather head straight down the outside of the structure to a ground electrode right there in the ground, then inside to any other electrodes.

Bob

If the power company's nice digital remote read meter gets blown up, who cares?

Seriously though, that does seem like the most logical place to connect the GEC, and the code does allow it. That said, to see it done would be a first in our area anyway, wouldnt it?

 

[iwire]

Re: Bonding meter can

Originally posted by peter d:

That said, to see it done would be a first in our area anyway, wouldnt it?

I have never seen it done that way and very few meters get the GEC.

In my area the most common place to land the GEC is at the service switch which is generally inside.

 

[peter d]

Re: Bonding meter can

Originally posted by iwire:
In my area the most common place to land the GEC is at the service switch which is generally inside.

I am seeing more and more GECs being landed in the meter now in National Grid territory. Does NStar allow it?

 

[Robbie Romex]

Re: Bonding meter can

Roger, your 2nd graphic shows exactly what I did except substitute a transfer switch for the 200 amp panel. IWIRE, no if we think of it in terms of "first and last" I went from ground rods to meter can to first means of disconnect with a continuous #4 THHN. Again, the bonding of the neutral is only as good as the neutral itself and besides, the power co.'s conductors are unfused. Without a redundant path to ground the house itself would become the path, wouldn't it? Either I am not understanding something (very possible) or this is a potentially serious problem. This has been bothering me for some time now.

 

[roger]

Re: Bonding meter can

Originally posted by Robbie Romex:
IWIRE, no if we think of it in terms of "first and last" I went from ground rods to meter can to first means of disconnect with a continuous #4 THHN.

Robbie, now you have a parallel neutral.

You only want the GEC bonding to take place at one location.

Your #4 would try to carry the full neutral load if the neutral itself were lost. This installation would also be in violation of 310.4

Edited to post a more accurate graphic.

Roger

[ July 30, 2005, 12:08 PM: Message edited by: roger ]

 

[iwire]

Re: Bonding meter can

First off I should say welcome to the forum Robbie.

Bonding and grounding can be tough subjects and many times are misunderstood.

My own knowledge of these systems increased ten fold once I started hanging out in these electrical forums.

Originally posted by Robbie Romex:
Roger, your 2nd graphic shows exactly what I did except substitute a transfer switch for the 200 amp panel. IWIRE, no if we think of it in terms of "first and last" I went from ground rods to meter can to first means of disconnect with a continuous #4 THHN. Again, the bonding of the neutral is only as good as the neutral itself and besides, the power co.'s conductors are unfused. Without a redundant path to ground the house itself would become the path, wouldn't it? Either I am not understanding something (very possible) or this is a potentially serious problem. This has been bothering me for some time now.

I am still unclear to what you actually have.


Rogers graphic has the GEC stopping at the meter can, but you said "I went from ground rods to meter can to first means of disconnect with a continuous #4 THHN."

If in fact you have run a continuous 4 AWG from the grounding electrodes, bonded to the meter can then bonded that conductor to the service disconnect enclosure you have a created an code violation.

That GEC you ran between the meter and the panel (ATS) is now in parallel with the neutral and a violation of 310.4.

Now this.

Without a redundant path to ground the house itself would become the path, wouldn't it?

What are you expecting this redundant path to ground to accomplish?

Even if you install this redundant path to ground if the utility neutral opens all the grounded objects in the structure will be at an elevated voltage potential related to the earth.

 

[iwire]

Re: Bonding meter can

To help us understand your service please tell us if this is what you have.

Service point > Service conductors > Meter > service conductors > ATS > feeder conductors > branch circuit panel.

If that is what you have I must ask if the ATS is service rated?

 

[Robbie Romex]

Re: Bonding meter can

250-90 Bonding shall be provided... to ensure...the capacity to conduct safely any fault current ( conduct to where ? the grounded or grounding conductor ?)
250-92 (a)The non-current carrying metal parts of equipment indicated in (1), (2), and (3) shall be effectively bonded together (2)All service enclosures containing service conductors, including meter fittings...

Is this accomplished by the bonding screw in the meter can? Maybe I'm having trouble seeing the difference in bonding between the line and load side of the service?? Maybe I should read up on the relationship of bonding to grounding? Most of my teachers in night school were unemployed E-2s! I'm glad I found this site!

 

[Robbie Romex]

Re: Bonding meter can

Roger,
I think that 310-4 is dealing with paralelling for reasons dealing with ampacity. It doesn't seem to be directed specifically at grounding/bonding issues as 250 is.

 

[iwire]

Re: Bonding meter can

Originally posted by Robbie Romex:
Roger,
I think that 310-4 is dealing with paralelling for reasons dealing with ampacity. It doesn't seem to be directed specifically at grounding/bonding issues as 250 is.

You call it a bonding conductor but that fact is the way you installed it you made it a neutral conductor.

As it is a neutral conductor 310.4 applies.

[ July 30, 2005, 04:38 PM: Message edited by: iwire ]

 

[iwire]

Re: Bonding meter can

Check out this code section

250.142 Use of Grounded Circuit Conductor for Grounding Equipment.
(A) Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground non?current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:

(1)On the supply side or within the enclosure of the ac service-disconnecting means

(2)On the supply side or within the enclosure of the main disconnecting means for separate buildings as provided in 250.32(B)

(3)On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1)

What this means is the neutral is used to ground the meter enclosure.

Twice you mentioned a green screw, I have never seen a green bonding screw used at a simple meter fitting.

Are you talking about a meter main breaker combo unit?

 

[Robbie Romex]

Re: Bonding meter can

IWIRE,
This was the first time I had seen such a screw too. Some of my co-workers were apparently aware of this. It was a milbank 200 amp meter socket enclosure. The screw is directly below the load side neutral lug. There was a tag that said "remove for ungrounded services" or something to that effect.
Have you read the book on bonding and grounding available through this site? Is it worthwhile or can I learn just as much from seasoned hacks, uh, I mean Journeymen?

 

[peter d]

Re: Bonding meter can

Originally posted by Robbie Romex:

Have you read the book on bonding and grounding available through this site? Is it worthwhile or can I learn just as much from seasoned hacks, uh, I mean Journeymen?

Robbie,

Definitely get some of Mike Holt's books on the subject. Stick around this code forum and ask questions. Look at how much you've learned allready, and you just got here. Journeymen can certainly teach you a lot, but what they teach you isn't always right. I have learned so more from the members of this forum that I've ever learned from a journeyman!!

 

[George Stolz]

Re: Bonding meter can

Robbie, welcome to the forum. The gang here, particularly Bob, have helped me tremendously in understanding this stuff. I hope you stick around.

Originally posted by Robbie Romex:
250-90 Bonding shall be provided... to ensure...the capacity to conduct safely any fault current ( conduct to where the grounded or grounding conductor ?)?

It doesn't say. Why? Because physics answers that for us.

Electricity is seeking any path back to it's source. So, you're asking, which path back to it's source, grounding or grounded? You can see the confusion, because it doesn't specifically lay out a cut-and-dried requirement, leaving options open.

You, personally have to determine the point where the grounding system begins to exist in an installation. If the point is acceptable in the meter can, then that is the point, and no connections can be permitted between the grounding and grounded conductors after that point. If that point is the disconnect, then that's where the "last stand" of the neutral serving as a "grounding" conductor is.

Maybe I should read up on the relationship of bonding to grounding?

Once it clicks, you'll be amazed at how simple it really is: look at the definitions.

NEC-2002 100-Definitions
Bonding (Bonded). The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed.

Grounded. Connected to earth or to some conducting body that serves in place of the earth.

The ultimate point of bonding: To provide a current path that will open OverCurrent Protective Devices (OCPD's) so that "faults" are killed quickly.

The ultimate point of grounding: Lightning protection and such.

So the connection to the neutral ahead of "that point" where the "bonding system", accomplishes it's primary function: If a hot conductor touches the case of the meter can, a "line-to-case fault" as Bob's picture showed, then the neutral will begin sending that fault current back to it's source, the transformer.

BTW, I've seen your meter can, I know exactly what you are talking about (maybe).

If your grounding system is connected to the meter can, and that ^&%*$ screw hidden under the neutral with the red tag on it is still in place, you have a parallel path for neutral.

Look at your meter can. Remove the neutral (mentally). Now there is a grounding conductor serving in place of the neutral between the meter can and the disconnect, because the neutral and grounding conductors touch twice, once in the meter can and once in the disconnect.

The lights are still on, it still has a path back to the netural. You can't do that. The "grounding" conductor will carry current even with the neutral in place, and will burn up.

 

[jwelectric]

Re: Bonding meter can

Is it legal to install a piece of rigid metal conduit between the meter and the main disconnect?

I agree that the grounded (neutral) is all that is required but it is NOT a requirement that no grounding conductor be installed as illustrated by the rigid conduit.

As Robbie pointed out in his first post 250.92 (A)(2) requires the meter and main disconnect to be bonded.

250.142 give us permission to use the grounded (neutral) to bond the meter and the main disconnect. It does not require that it be the only bond between the two.


I can see where some would think that to bond the meter can with a conductor would violate 310.4 but I must say that this is pure hogwash.
If this was a violation of 310.4 would not the piece of rigid conduit be the same violation?

I do not agree with the #4 being ran from the ground rod through the meter to the main but I see no code violation either.

 

[iwire]

Re: Bonding meter can

Originally posted by jwelectric:
Is it legal to install a piece of rigid metal conduit between the meter and the main disconnect?

No, it was and is a common practice.

I have opted to use a PVC section in these areas to avoid this issue.

Originally posted by jwelectric:
I agree that the grounded (neutral) is all that is required but it is NOT a requirement that no grounding conductor be installed

I agree, there is no section in the code that prevents two grounding paths.

Originally posted by jwelectric:
as illustrated by the rigid conduit.

I don't agree, I will explain below.

Originally posted by jwelectric:
I can see where some would think that to bond the meter can with a conductor would violate 310.4 but I must say that this is pure hogwash.

Thanks for calling my opinion hogwash.

Originally posted by jwelectric:
If this was a violation of 310.4 would not the piece of rigid conduit be the same violation?

No it is not the same violation.

Notice 310.4 specifically does not mention EGCs.

310.4 is about conductors as described in 310.13 not EGCs as described in 250.118. All types and sizes of grounding conductors are in parallel in any installation. Clearly 310.4 does not apply to EGCs or we all wire violations daily.

Here in this case we are talking about a parallel neutral, not a parallel grounding conductor.

Think your argument through, if we accept that 250.118 makes a metal raceway equivalent to a conductor as described in 310.13 you would have to accept using only the raceway as the neutral current path between the meter and the panel. (no wire)

Let me ask this.

Would you say it is a good idea to parallel a 2/0 copper neutral conductor with a 4 AWG copper bonding conductor when you are well aware they are current carrying conductors?

[ July 31, 2005, 11:11 AM: Message edited by: iwire ]

 

[jwelectric]

Re: Bonding meter can

Iwire

Please forgive me if I insulted you with my statement of 310.4 being hogwash.

I was trying to point out that should a rigid conduit be installed between the meter and panel that it would be in parallel with the grounded (neutral) conductor.

I also pointed out that 250.92 (A)(2) requires that the meter can and the main panel to be bonded together.

I also pointed out that 250.142 (A)(1) permits the grounded (neutral) to act as this bonding conductor.

In Robbie?s original post he stated, ?I recently had a local inspector flunk a new service because I bonded the meter can to the service.?

This is not a violation therefore we should be telling Robbie that he has complied with the letter of the code instead of, well what has been said.

If for some reason or the other we don?t like this arrangement then make a proposal to change it. Don?t forget that a transformer secondary has the same problem when the system bonding is done in the panel. What we don?t need to be doing is telling some one that the code doesn?t allow the bonding of the panel and meter base.

Yes I see the problem with the paralleling of the grounded and bonding between the two, but until the Code Making Panel addresses this it is legal.
I do believe that you have made the statement that the wording of the code is what is to be enforced not what we think or our opinion.

 

[roger]

Re: Bonding meter can

JW,

What we don?t need to be doing is telling some one that the code doesn?t allow the bonding of the panel and meter base.

look at the graphic below and then revisit your statement that I quoted, no one has said what you think they said. :roll:

Roger