Grounding of subpanel In Townhouses

[MIKEWVA]

I have a similar situation with same setup and am looking for some clarification/help. I have a 800amp service disconnect panel with a 4 bank meter stack off of it on the outside of a four unit townhouse complex. Each meter has it's own service disconnect breaker for each meter which feeds each townhouse tenant. The panel inside one tenant townhouse is a 100amp subpanel fed with 2hots,neutral and ground from outside meter breaker.
My question is what is the grounding and bonding requirements for the service equipment and also the subpanel in the townhouse.

Currently service has one ground rod and one cold water to main incoming water line which is also used for all townhouse tenants.
Subpanel has only the feeder with separate neutral and ground conductors and a #6 bond wire out of subpanel to same cold water pipe and hot water copper tubing.

I have a inspector telling me I need to drive a ground rod for each subpanel in each tenant which I feel is incorrect and creating a potential hazard. Can you confirm the service and the subpanel the way it sits meet the current code? And if not what code section am i missing here.

 

[Dennis Alwon]

I moved the post here as it was in another thread.

Are these townhouses attached or are they separate structures. Technically if they are attached then no ground rod is needed for the subpanels. If the inspector is seeing this as separate structure because there are firewalls between them then perhaps he has an argument but IMO, no rod is needed for the subs.

 

[102 Inspector]

If these were considered separate structures due to firewalls, I would think there would be an issue with running feeders through someone else property with easements. If considered one structure, I would not look for any additional grounding at the sub-panel other than the 4-fire feeder for the main disconnect and separated grounded and grounding conductors. I am guessing from what I am reading the inspector wants you to drill through the slab to drive a ground rod.

 

[DrSparks]

Subpanel has only the feeder with separate neutral and ground conductors and a #6 bond wire out of subpanel to same cold water pipe and hot water copper tubing.

Are these connections made within 5 feet of entrance of the water main? As I've always said, the water main should never be considered a ground electrode, but rather something that needs to be bonded to prevent a voltage difference between the metal water piping and ground. The same goes for all metal systems in the structure. It can, however, be used as a common GEC if the terminations are made within 5 feet of entry (unless exception applies).

From an engineering standpoint, I would suspect that your ground impedance would be something that needs to be checked out. From a strict Code perspective, I don't believe the inspector could compel you to install additional ground rods, although it certainly wouldn't be a bad idea. However, for a ground rod system to be effective, you would need to install many, many of them, as far apart as possible. A single ground rod really does almost nothing in the way of reducing ground impedance. Did you look to see if the original concrete workers left a piece of rebar stubbed up out of the slab? That would be your best bet!

 

[DrSparks]

IMO, no rod is needed for the subs.

I agree, as long as the foundation is continuous, it is a single structure, regardless of how the upper floors are demised.

 

[DrSparks]

I would think there would be an issue with running feeders through someone else property with easements.

Welcome to the world of condos. Pretty much all condos are wired that way here in Wisconsin. The legal issues of this confound me!

 

[Dennis Alwon]

If these were considered separate structures due to firewalls, I would think there would be an issue with running feeders through someone else property with easements. If considered one structure, I would not look for any additional grounding at the sub-panel other than the 4-fire feeder for the main disconnect and separated grounded and grounding conductors. I am guessing from what I am reading the inspector wants you to drill through the slab to drive a ground rod.

I don't know of a code section that will not allow a feeder(as these are) to run thru the buildings. Service conductors would be different

230.3 One Building or Other Structure Not to Be Supplied
Through Another. Service conductors supplying a building or
other structure shall not pass through the interior of another
building or other structure.

 

[jaggedben]

'Townhouse' to me means not separate building by definition. If we can rely on that then I think the inspector is just wrong.

There's absolutely no physical relationship between firewalls and grounding. If people are going there, then 'building' should be eliminated from 250.32.