Bonding Separate Building's GES Together

[Platinum]

Hey guys could use your input on this.
Scenario: School campus with multiple buildings and service utility transformers.
I have a new classroom building that is being served by a new dedicated, utility transformer. This building is on a school campus with multiple buildings where each building has its own service utility transformer and its own grounding electrode system.

The plans reviewer has requested us to run a #3/0 bare conductor to connect the new building?s GES to the neighboring existing building?s structural steel. His argument is that the service transformer is an SDS and requires common electrodes to be bonded together. My thoughts are this is not an SDS and per definition of an SDS, it specifically states the words "other than service". His other reason is that there are copper communications, fire alarm lines, and an exterior metal canopy that connect the 2 buildings together where a lightning strike could cause equipment damage.

Would it hurt to bond a separate building to the new building?s GES? Wouldn?t a short circuit in one building travel next door to the other building?s GES?
Thanks for your help.

 

[ActionDave]

You are correct, a separate building with a separate service, and a separate utility transformer is not a SDS. There is no requirement to bond the grounding electrode systems together.

There is no real danger in it..... not much different than neighbours all sharing the same metal water pipe system.

 

[don_resqcapt19]

Is it really a service? Does the building have its own meter? In many cases, with campus type installations, the owner buys power at the primary voltage and there is only one service for the complete campus. The rest is feeders and SDS.

 

[kwired]

Even if the transformers on campus are SDS's instead of services there is no requirement to bond the GES of two separate buildings together. I don't believe there is anything prohibiting it either though, other then if there should be objectionable current flow by the way it is done - but avoiding connecting to the grounded conductor and instead connecting to the equipment grounding conductor should eliminate that issue.

 

[Platinum]

Is it really a service? Does the building have its own meter? In many cases, with campus type installations, the owner buys power at the primary voltage and there is only one service for the complete campus. The rest is feeders and SDS.

Yes, there are utility owned transformers with dedicated meter.
I have seen what you are talking about before too where the school owns the primary but this is not the case here.

 

[Platinum]

Even if the transformers on campus are SDS's instead of services there is no requirement to bond the GES of two separate buildings together. I don't believe there is anything prohibiting it either though, other then if there should be objectionable current flow by the way it is done - but avoiding connecting to the grounded conductor and instead connecting to the equipment grounding conductor should eliminate that issue.

I think the inspector had 2 concerns here that i think are separate issues:
1- 250.30 (4) [2008 NEC] Grounding electrode conductor multiple separately derived systems. Again it can be argued that this is a service instead of SDS, so this is not required.

2- 250.94 - Bonding for other systems - intersystem bonding. He wanted to 2 GES's bonded together since there are some common metallic pathways (canopy structure, fire alarm, intercomm).

 

[kwired]

I think the inspector had 2 concerns here that i think are separate issues:
1- 250.30 (4) [2008 NEC] Grounding electrode conductor multiple separately derived systems. Again it can be argued that this is a service instead of SDS, so this is not required.

2- 250.94 - Bonding for other systems - intersystem bonding. He wanted to 2 GES's bonded together since there are some common metallic pathways (canopy structure, fire alarm, intercomm).

1- if the transformers are POCO owned/controlled - there is no argument each building has a separate service, only thing different on a campus is each building is under same owner/manager - but each is still otherwise independent just like a residential or business district where each building is also supplied by a separate service.

2 - From 250.94:

An intersystem bonding termination for connecting intersystem bonding conductors required for other systems shall be provided external to enclosures at the service equipment or metering equipment enclosure and at the disconnecting means for any additional buildings or structures.

No where does it say it needs extended to other structures, just that each structure needs a intersystem bonding termination.

This is no different then the fact you do not need to bond anything from your house to your next door neighbor's house - assuming they are separate structures, and you still wouldn't have to should you decide to purchase that house next door or even if you set them up so both are on same metering you still wouldn't need to run any kind of bonding conductor between them, they are stand alone structures each with it's own power supply whether it be service or a feeder.