Copper Water Lines Between Main and Accessory Structure

[electricus23]

Hi -

Doing some work initial planning for a project where there are two structures on the property.

The meter and main panel (w a service disconnect) are located at structure B. The main panel acts as main disconnect and is where the MBJ is located. The GEC is a ground rod (old structure, no continuous concrete to support ufer).

The main electrical panel feeds a the sub panel in the structure B (PVC underground). The main panel also feeds branch circuits within the same structure B.

The water main for the property runs to the accessory structure which feeds boilers/water heaters for the whole property - water back feeds from here to the main structure.

The copper pipe from the water main has as clamp and ground wire running to the Main panel ground bar.

Okay, now on to Structure A.

Structure A panel is fed from Structure B. Structure A has a conduit through the foundation going into a panel inside with a main breaker. The feed has L1, L2, N, and EGC. No disconnect outside observed. I believe this is appropriate given the main breaker on the panel and the feed flowing underground through slab.

There is a ground rod here as well - looks like an afterthought - drilled in through the sheathing - but appears proper. It is tied to the same ground bus bar where the EGC from Structure B is also landed.

Structure A has copper water lines entering from an underground feed from Structure B. 3 lines - hot cold recirc. None of these 3 lines are tied to a ground as far as I can tell.

Last thing here, adding to complexity, there is a concrete addition going in on the main structure A - far end from panel location. This will have a concrete slab, where an ufer will be required.

My concerns:
1. Risk of creating ground loops

I may be overthinking this, but isn't there an issue here for ground loop given each structure has a ground rod, and the water main is bonded as part of the GEC but not the water feeds between the buildings? I think the feeder water pipes should be grounded somewhere to meet entrance grounding requirements?

2. How to tie in to the new concrete slab ufer

The client is asking for the most robust/data center level grounding to reduce exposure to sensitive technology components (stock broker trading equipment I gather).

What I was planning to suggest was the following:
1. New ground ring around structure B tied to act as the service and main GEC, replacing the single ground rod. Bond the water main ground clamp to the ground ring.

2. New ground ring around structure A

3. Bond Ufer to ground ring while it passes by the addition footprint

4. 3 x 1" water lines clamped and bonded to the ground bus at the structure A sub-panel

There is waterproofing going on across all of the existing foundation walls so someone else would be handling the trenching for the ground ring. 'money is no object' type customer so I get this may be a bit overkill for other projects.

What am I missing? How can I approach this best?

Open to all feedback on how to best approach. Thanks!

 

[augie47]

Under present Code (and even under the 250.32 exception due to the common water lines) IF building "A" is going to be fed from Building "B:" there must be a EGC along with the feeder.
In addition, if you are under 2017 or earlier you can only have 1 feeder from Building B to Building A and Building "A" needs a disconnect meeting the requirements of 225.32

Is this a dwelling unit ?

 

[don_resqcapt19]

As long as there is only one neutral to ground connection at the service equipment, multiple connections of the EGC do not create ground loop currents as there is no current on the EGCs unless there is a fault.

 

[electricus23]

Thanks for the reply. The building B feeder to building A is a 4 wire feeder. At the sub-panel in Building A, the EGC is landed to the ground bus bar along with a wire coming from ground rod. This part seems correct.

However, in Building A, there are a few EMT raceways in the mechanical room with the sub-panel feeding appliances. I need to verify that these EMTs are tied out to the ground bus bar. Just realized I had not verified that.

The feeder enters Building A encased in concrete and goes directly into the bottom of the sub-panel (3.5 ft probably from exiting concrete to bottom of panel). The sub-panel has a 200A disconnect, and the MDP feeding the sub has a 200A breaker. I believe we are compliant here with 225.32 for 2017 and current.

Residential, yes but not MDU. I think they were saying building B was staff quarters at one point, now just looks like storage/cottage. Building A is the main house. The addition on Building A is mostly called out to be a home office, which is where some trading equipment is going.

So it is sounding like the water pipes connecting the two buildings needs to be added to ground bus bar in Building A.

And is there any thoughts on needing to worry about ground loops with this setup?

 

[electricus23]

As long as there is only one neutral to ground connection at the service equipment, multiple connections of the EGC do not create ground loop currents as there is no current on the EGCs unless there is a fault.

Nailed my concern, thank you very much!

EDIT: Does the addition of two independent ground rings acting as each panel's GEC cause for concern? Different ground potentials, perhaps?

 

[don_resqcapt19]

Nailed my concern, thank you very much!

EDIT: Does the addition of two independent ground rings acting as each panel's GEC cause for concern? Different ground potentials, perhaps?

They can't really be independent as they are connected via the feeder EGC.

 

[electricus23]

They can't really be independent as they are connected via the feeder EGC.

Good point, all makes sense. Thank you!

Is the ground ring approach heavy overkill? Or not super unreasonable? Is it appropriate to use the ring as a bonding point for the ufer?

 

[don_resqcapt19]

Good point, all makes sense. Thank you!

Is the ground ring approach heavy overkill? Or not super unreasonable? Is it appropriate to use the ring as a bonding point for the ufer?

Grounding electrodes, in general are overkill. You can connect the concrete encased electrode to the ground ring.
If you have a concrete encased electrode, there is no code or technical reason to install any additional electrodes.