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#187377 - 06/24/09 07:31 PM Grounding / Bonding Riddle
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
The 2008 NEC did a pretty good job regarding separate structures, from the same meter, requiring one to be the 'main' and the others 'subs.' That is, every panel after the first needs to have the neutrals segregated from the grounds.

My current job does a fine job of bringing this issue back to life.

Here is the situation: Each of three mobile homes have their own panels, mounted on a post next to each trailer.

The panels all go back to a common board, where each has its' own main breaker / meter. These are fed from a gutter attached to the fused disconnect switch. The PoCo feed is a drop to that switch.

The 'pedestals' are fed from the disconnects by PVC conduit (buried). Service drop is overhead. The disco, gutter, and meter/mains are all steel, with rigid connections.

Disconnect and panel both come with green bonding screws. The meter/main does not - instead, the neutral buss is quite solidly bonded to the case, and the neutral buss has a smaller additional lug (aparrently for a GEC).

Before I tell yuo what I did - I'm not completely happy with my results) - I'd like your thoughts on two issues:

1) Where would you attach the GEC(s), place the ground rod(s)?

2) Where would you bond (or separate) the grounds from the neutrals?

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#187378 - 06/24/09 07:47 PM Re: Grounding / Bonding Riddle [Re: renosteinke]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
I may not understand the exact situation but I would call that whole cludge around the service disconnect as the service equipment and that will all be bonded to the neutral via the MBJ the bonded neutral bar in the can where the service disconnect resides. I would put the GEC there too but it can go anywhere from there to the service point.
The EGC will bond all the ground buses. The neutral will "float" through.
_________________________
Greg Fretwell

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#187384 - 06/25/09 07:57 AM Re: Grounding / Bonding Riddle [Re: gfretwell]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
Be nice to see a one line , But Mobile homes comes under 550.
Service equipment is 550.32.

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#187387 - 06/25/09 09:36 AM Re: Grounding / Bonding Riddle [Re: Yoopersup]
Alan Nadon Offline
Member

Registered: 03/10/05
Posts: 398
Loc: Elkhart, IN. USA
The fused disconnect ahead of the meters is what muddies the water. It becomes the service disconnect. The AHJ might consider the entire assembly to be the Service.
The ground rod would be at the fused disconnect, up to the point of attachment by the POCO. The Main Bonding Jumper would be in the fused disconnect.
The bonding of the grounded conductor (neutrals) in the meters are inheirent in the design of the meters. A problem the utility and the inspector have to resolve.
The disconnects on the load side of the meters would not have the grounded conductor bonded.
Better design would be to remove the fused disconnect. Or remove the fusing so it doesn't qualify as a service disconnect. Then the bonding could be done in each metered disconnect, with a connection to the ground rod (s) from each. Usually the utility does NOT want any accessable point ahead of their meters so removing the fusing and locking the disconnect could be the easiest way out of the problem.
_________________________
Alan--
If it was easy, anyone could do it.

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#187388 - 06/25/09 11:30 AM Re: Grounding / Bonding Riddle [Re: Alan Nadon]
Tom Offline
Member

Registered: 01/01/01
Posts: 1069
Loc: Shinnston, WV USA
I run into a similar situation when the mobile home owner (and sometimes at a mobile home park) locates the service disconnect further than 30 feet and/or not in sight of the home.

The answer to this is to follow 550.32(A) and install another disconnect that is service entrance rated. Then go to 250.32 & pick one of the options based on new installation/existing installation. Generally, the easiest would be to install a 4 wire feeder (required if new construction), splice the neutral at the second disconnect & insulate it, use the neutral bar to land the equipment grounds (install the bonding jumper), install grounding electrodes & connect to the equipment ground, install 4 wire feeder to mobile home, send invoice to owner.

Grounding & bonding at the meter pack would be handled by installing the required electrodes & MBJ if the neutral is not factory bonded to the enclosure.
_________________________
Few things are harder to put up with than the annoyance of a good example.

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#187399 - 06/25/09 07:30 PM Re: Grounding / Bonding Riddle [Re: Tom]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
I completed the job today, and inspection is tomorrow. I ought to have some pics later tonight.

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#187404 - 06/26/09 01:20 AM Re: Grounding / Bonding Riddle [Re: renosteinke]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
OK ... I'm having some troubles with the 'electrical photos' site, so I've had to use 'photobucket' instead. I'll fix that later.

Here;s an overview. You can see the panel that will feed the trailer in the foreground, and the side of the meter board a bit farther back. Note that there's a ground rod here - I treated it as if it were the separate structure. Inside, I isolated the ground from the neutral, and fed it with four wires from the meter board.



Here's a better view of the meter board. Kludge? Greg, you broke my heart laugh. Note the ground rod coming from the fused disconnect:



While you see only one meter base, there will later be two more added. I chose a disconnect to ease my future work - and then fused it because I want to know if there are problems. Let's just say that this customer likes to 'cheat' the system, even when he has no idea what he's doing.

Now, here's the meter / main insides .... whech is where the trouble arises:



As you can see, the neutral is factory bonded to the case. Though I've passed my ground wire through the partition, direct to the trailer pedestal, there's no denying that some neutral current will pass through the sheet metal on its' way back to the transformer.

Why did I put the ground rod at the disconnect? Because it serves the entire board; it really doesn't belong with any individual meter - and running a separate GEC from each meter / main seems silly.

Not bond the case of the disconnect to the neutral there? Then the GEC would depend on the various sheet metal connections to reach the bond at each meter / main.

I think you can see why I'm not happy with this arrangement, and seek your thoughts.

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#187405 - 06/26/09 01:55 AM Re: Grounding / Bonding Riddle [Re: renosteinke]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Sorry Reno, no offense intended, I was just a a loss for a better word for the assembly of cabinets around a complex service arrangement like that.
I have heard it said that the whole assembly is the service for the purposes of where you ground the neutral and it may actually happen more than once. Typically meter bases bond the neutral in addition to the MBJ we install.
Is this the meter from the utility or a private meter from the park owner? I agree with the opinion above, utilities don't usually let you get at connections on the line side of their meter without breaking a seal. They may not want fuses in there that you have to access.

This is from the handbook, although not exactly the situation you have you see there are multiple places where the neutral is bonded.


_________________________
Greg Fretwell

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#187410 - 06/26/09 06:50 AM Re: Grounding / Bonding Riddle [Re: gfretwell]
harold endean Offline
Member

Registered: 02/16/02
Posts: 2248
Loc: Boonton, NJ
Greg,


Couldn't Reno use all of the equipment by the disconnect as "Service" and everything else would become the sub panels? Also I know you are suppose to bring the ground rods back to the main service equipment, but couldn't he attach the ground rod to the grounding conductors in the sub panels by the trailers? After all the area from where the trailers are to where the main service might be accessible before all of the trailer slots are used up.

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#187412 - 06/26/09 08:29 AM Re: Grounding / Bonding Riddle [Re: harold endean]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
These meters will be read by the PoCo.

Greg, that is a great bit of art, and directly applies to this situation.

In essence, you're saying that we avoid the "parallel path" issue by considering all the 'kludge' (:D) as if it were one big cabinet. That being the case, the use of bonding bushings, etc., takes on an additional importance.

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