two connected condominiums sharing 2 ground rods

E

Electric_kool_aid

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Location
Washington
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Journeyman 02
so basically what i have is two separate condos (each has its own 200 amp meter and panel) but they are connected as one building. according to 250.30 (6) i believe those two units can share the same grounding electrode system. the panel next door was recently replaced so i was hoping to connect to the new ground rods that are out there for that unit. anyone have any advice? any issues with this?
 
Electric_kool_aid said:
This is basically how it is ran, continuous. Thank you for response
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And just for clarity:

As long as each GEC from service to nearest rod is unspliced, the continuous requirement is met.

Actually running the entire pathway in one continuous wire merely saves on rod-clamp quantity.

And you're welcome . . . again.
 
You will have objectionable current not only with the common Driven Electrodes but if you have shared metallic water piping there will most likely be current on these piping systems.
 
Electric_kool_aid said:
So it’s no different from having 2 panels in a single home?
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Exactly. All qualifying electrodes in and around a premises must be connected together as a single electrode system.

To isolate nearby electrodes from one another can force high currents to flow through wires not intended and even through structures due to voltage gradients caused by nearby lightning strikes.
 
Electric_kool_aid said:
And why is that? So you’re saying I should pound two more ground rods ?
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No, there would be no real benefit. Any number of grouped main disconnects may and should share the same two rods.

He's saying that interconnected metallic water supplies might have the same kind of currents as shared rods, and what triggered your asking your original question.
 
LarryFine said:
That's what we all want. What seems contradictory to you?
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Just what Brian said, objective current doesn’t ever seem to be a good thing, inspector passed it but he even mentioned some slight concern for whatever reason. Grounding just is not something I ever want to mess with! Thanks for all the feedback really appreciate it
 
This is an unfortunate effect of how we do electrical services in the US.

Whenever you have multiple connections between neutral and ground you have the opportunity for 'objectionable current'.

The only way to avoid this would be to get rid of the neutral to ground bond in each service (or get rid of the common neutral shared by multiple services).

Your installation is to code, and in this case the 'objectionable current' is probably not a significant problem. But it is really there, and you could imagine situations where it would matter. Eg. Condo A loses its neutral, but no one notices because the current returns via the grounding connection to Condo B's neutral.

If there is any shared metal between the two condos (shared service drop, shared phone or cat drop, pipes that go through one to the other, etc ) then IMHO it is better to share the ground electrodes because of the point in post 12. Basically soil current can enter one set of electrodes, go through the shared metal, and exit through the other set of electrodes. Better to just have a single common electrode set.
 
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