Grounding and bonding

[firebird]

I have a tricky one.
So client has two buildings. Both buildings have their own meter and each have their own bonded and grounded main panel.

But building one runs a subpanel that runs to building 2. They do not have that subpanel attach a ground rod which is required when you have a detached building.

For the reason why they have a subpanel running from building one to building two versus hooking that sub panel to the meter within the same building is that they have a solar backup system only on meter 1. Which they wanted to move a bunch of circuits to that system from building 2.

Now if I were to connect that subpanel to the ground rod that's already connected to service meter 2 wouldn't that cause a loopback potential issue. Or should I just run two separate ground rods to that sub panel.

 

[Dennis Alwon]

So client has two buildings. Both buildings have their own meter and each have their own bonded and grounded main panel.

Are you saying that there are 2 meters on building one and each meter feeds a service disconnect at the building? I am confused by the rest of your post

 

[firebird]

Are you saying that there are 2 meters on building one and each meter feeds a service disconnect at the building? I am confused by the rest of your post

No there is 1 meter on building 1. They run a subpanel from building 1 to building 2. Building 2 is a detached building 300 ft away which would require your sub panel to run to a ground rod.

Yet this building 2 has its own meter. So a completely separate service.

Now if I run that sub panel grounding wire to the rod will that cause a loopback between both services?

And again the reason why that sub panel is not connected to meter 2 service is because meter one has a solar battery backup system so they wanted some of the circuits in that building designated just to the solar system.

 

[Ponchik]

So they have two buildings with two services one at each building and each building has the proper grounding system. Now, building TWO has a sub panel that is fed from building ONE. Your concern is that sub panel is not connected to a grounding electrode.

IMO, each building can only have one service or feeder. If that is not a concern, then the building already has a grounding system, there is no need to connect the sub panel to the grounding electrode.

 

[firebird]

So they have two buildings with two services one at each building and each building has the proper grounding system. Now, building TWO has a sub panel that is fed from building ONE. Your concern is that sub panel is not connected to a grounding electrode.

IMO, each building can only have one service or feeder. If that is not a concern, then the building already has a grounding system, there is no need to connect the sub panel to the grounding electrode.

Correct. you can see the dilemma here. As you stated you can only have one service per building. Which service one enters the second service building in a form of just a sub panel. It's probably why they have that rule is so you don't cause a loopback between two separate services and that's why I was asking as this is something you never see.

It's mind-boggling on this setup. I wouldn't be surprised seeing more people trying to do this with all these solar systems popping up everywhere.

 

[LarryFine]

IMO, the sub-panel in bldg. 2 should be bonded to that building's existing GES (and not a separate one.)

Grounding-conductor loops are not a concern like grounded-conductor loops would be.

 

[firebird]

IMO, the sub-panel in bldg. 2 should be bonded to that building's existing GES (and not a separate one.)

Grounding-conductor loops are not a concern like grounded-conductor loops would be.

Well this is my thought process.

You have a transformer that is supplying two buildings right next to each other.

Each building has its own meter.

You have a neutral wire of course it runs to both buildings. A neutral wire can be live if something is hooked up wrong or some kind of fault.

So let's say you have building one has a a subpanel to building 2. Yet building 2 has its own separate service.

Which you have you're two hots, you're neutral and a ground wire connecting your sub panel from building one

Now if you have building two let's say has a fault.

But you have the sub panel from building 2 connected to building 1 grounding system connected together.



You can in theory have a loop where that neutral wire loops to both services and carry current through the ground wire. Since this is interlinked.

Mike Holt explains perfect on how this happens on YouTube video. skip to 8.5 minutes in . Guy died removing a ground wire.

You wouldn't suspect a ground wire to be hot but in this case it would be. Since the equipment grounding completed the path.

 

[wwhitney]

Two neighboring buildings with utility services can have a neutral loop for a variety of reasons--via a metal water line, cable or telephone, maybe others. Run a feeder from one building to the other, and now the chance of the neutral loop is much higher--to avoid it you'd need to be sure the separate EGCs systems are never interconnected, directly or indirectly (both bonded to the same conductive metal).

Given the difficulty of doing that, the downside of a direct connection from the feeder EGC to the other building's GES, and the resulting neutral loop, are less (i.e. there is a good chance of there being a neural loop already). So the upside may outweigh that. Regardless, I think Article 215 would require the GES connection?

Cheers, Wayne