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#99525 - 08/10/06 06:10 PM 1200A service 3 400A disco where is point of service
crl22191 Offline
Member

Registered: 07/20/04
Posts: 11
Loc: va
Hi everyone,

We are building the service for an apartment building and are getting several different stories about where to bond the neutrals and grounds together. Here is the scenerio: CT cabinet with trough mounted directly to the side of it. 3 4" conduit runs to feed 3 400A disconnects. The neutrals all will land in the CT cabinet. The engineer is saying all neutrals and grounds (cold water, grounding electrodes, and grounds going to each 400A disco) should be bonded in the trough. Another theory is that the neutrals and grounds should be bonded in each disconnect. Does anyone know what the real deal is? Your input is appreciated.

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#99526 - 08/10/06 06:43 PM Re: 1200A service 3 400A disco where is point of service
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
It gets bonded in each service disconnect but the handbook also has an example with a bonded neutral bus in the trough and the bonds in each disconnect that is troubling to me. 2002 HB ex 250.12

edit to add pic




I think you will have neutral current flowing in the enclosres and nipples in this example.

[This message has been edited by gfretwell (edited 08-10-2006).]
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#99527 - 08/10/06 06:54 PM Re: 1200A service 3 400A disco where is point of service
crl22191 Offline
Member

Registered: 07/20/04
Posts: 11
Loc: va
are you saying that the neutrals should be bonded together in the trough but not the grounds? To me that would make no sense because they are already bonded together in the CT cabinet. If they get bonded in each disconnect does that mean we need 3 seperate cold water grounds and 3 seperate sets of grounding electrode conductors? We were liking the engineers suggestion because we could bond everything in the trough so we would only need to pull 1 cold water and 1 to the rods.

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#99528 - 08/10/06 06:59 PM Re: 1200A service 3 400A disco where is point of service
crl22191 Offline
Member

Registered: 07/20/04
Posts: 11
Loc: va
thanks for the pic, i see what you are saying about the neutral current, we happen to be using pvc and pulling a ground so i guess that alleviates that concern. Looks to me that this indicates the engineers method would be acceptable.

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#99529 - 08/10/06 07:09 PM Re: 1200A service 3 400A disco where is point of service
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Where you bond the neutral and where you land the ground electrode conductor are two separate things. You can attach the ground electrode conductor anywhere from the service point to the service disconnect but the neutral should onl;y get bonded in the service disconnect. Also you can tap in supplimentry electrode conductors and the GEC to each disconnect. In reality only the biggest one needs to be unspliced.

[img] http://members.aol.com/gfretwell/250ex26.jpg [/img]

[This message has been edited by gfretwell (edited 08-10-2006).]

[This message has been edited by gfretwell (edited 08-10-2006).]
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#99530 - 08/10/06 07:23 PM Re: 1200A service 3 400A disco where is point of service
crl22191 Offline
Member

Registered: 07/20/04
Posts: 11
Loc: va
well in the picture the neutrals and grounds are bonded in the trough, not in the disconnects. What you are saying though, is the neutrals pass right through the trough into each disconnect, while a ground bar can be installed in the trough to land the cold water ground, ground rod, and the individual grounds to each disconnect. One other thing, would the grounds to each disconnect be sized by 250.66 or 250.122?

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#99531 - 08/10/06 07:27 PM Re: 1200A service 3 400A disco where is point of service
crl22191 Offline
Member

Registered: 07/20/04
Posts: 11
Loc: va
thanks for the additional pic, it seems they indicate completely different points of bonding the neutrals and grounds, the first in the trough, the second in the individual disconnects

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#99532 - 08/10/06 07:28 PM Re: 1200A service 3 400A disco where is point of service
crl22191 Offline
Member

Registered: 07/20/04
Posts: 11
Loc: va
well i guess in the first pic they are bonded both in the trough and in the disconnects

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#99533 - 08/10/06 07:43 PM Re: 1200A service 3 400A disco where is point of service
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Bonding in both places is troubling. I wonder if they have fixed that example.
I do see people who assume everything in that cludge is part of the service disconnect and they bond everything to everything every chance they get. If you have a metal raceway back to the transformer where everything gets bonded again it is probably a distinction without a difference.
This is one area where you can have academic discussions about where the current is flowing but in reality it is probably everywhere in all of those cans, raceways and grounded/grounding conductors to some extent.
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#99534 - 08/11/06 06:10 PM Re: 1200A service 3 400A disco where is point of service
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Multiple points of bonding on the line side of the service disconnects are pemitted by the code.
Don
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