# Multi-Family Dwelling Grounding



## Adam B (Feb 13, 2021)

I am replacing the service entrance cable on a residential property that feeds three individual meter bases (not a multi-gang meter base setup, just three individual meters that are nippled out of a 4"x4" wireway where the line side meter base feeds are all spliced). The grounding is not up to code, and I've been getting multiple answers from local inspectors as to what the requirements are. The setup is a house that was split in half (lower apartment and upper apartment) and then a detached garage with a small apartment above it. Each of the panels in the house are rated for 100A and then panel in the detached garage is rated at 60A. Each house apartment leaves the meter base and is fed with an SEU cable. The garage apartment is fed with an SEU cable, then splices to a triplex (roughly 75' run), then splices back to an SEU cable that feeds the garage apartment panel. The property is on city water, so there is a water meter to consider with this setup, and there is only one meter that feeds all three dwellings. In speaking with local inspectors, I'm being told that I need to run a #6 from the water meter to each house panel, as well as, a #6 from a ground rod at the meter bases to each house panel, and then I'm to drive two ground rounds at the detached garage apartment. I was also told that I need to install 100A disconnects after the meter bases for the house apartments because they are not separated by a firewall (the house split was just blocking off the stairway from the first to the second floor), which would then by code would require me to sun an SER from the disconnect to each house panel.

I'm getting mixed answers from the same inspection agency, so I was curious to see what anyone else had to say. TIA.


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## jw0445 (Oct 9, 2009)

What you are describing is exactly how I would do it.


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## HertzHound (Jan 22, 2019)

To me all the service disconnects need to be at one location. So add three enclosed breakers under the meters. Add two ground rods near the trough, and run #6 to the trough. Run the water ground to the trough. Install a ground bar in the trough. Size the water ground to the service entrance conductors in the riser. Size the grounding electrode tap conductors by the size of the feeder taps to the meters.

Run SER to each apartment. At the garage you need to add another ground rod, and run that to the garage sub panel. The garage sub panel would also need a main breaker. The other two can be main lug.


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## Quickservice (Apr 23, 2020)

HertzHound said:


> To me all the service disconnects need to be at one location. So add three enclosed breakers under the meters. Add two ground rods near the trough, and run #6 to the trough. Run the water ground to the trough. Install a ground bar in the trough. Size the water ground to the service entrance conductors in the riser. Size the grounding electrode tap conductors by the size of the feeder taps to the meters.
> 
> Run SER to each apartment. At the garage you need to add another ground rod, and run that to the garage sub panel. The garage sub panel would also need a main breaker. The other two can be main lug.


I have never driven a ground rod for a sub panel such as his, the bond coming from the main seems sufficient... but it surely wouldn't hurt. I have had inspectors insist on bonding the water pipe when virtually everything including the run from the street meter was plastic.


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## Dennis Alwon (May 9, 2009)

I agree with the others that all the grounding should be run to the wireway above the panels. The grounding electrode conductor to the water pipes should be sized from the service conductors. I would calculate which of the two- the riser conductors or the taps are larger. Size the grounding electrode conductor to larger of the two.


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## HertzHound (Jan 22, 2019)

Quickservice said:


> I have never driven a ground rod for a sub panel such as his, the bond coming from the main seems sufficient... but it surely wouldn't hurt. I have had inspectors insist on bonding the water pipe when virtually everything including the run from the street meter was plastic.


If it’s a separate structure, it needs another ground rod. The structure could be a building or just a post in the ground with a panel on it. I’d have to look it up to see if the 25 ohms has to be proved again, or if just one rod is sufficient. I just put in two everywhere. At this point I would think it’s a auxiliary grounding electrode, so one would be sufficient? Kinda like some jobs want a ground rod at each light pole in a parking lot?


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## samgregger (Jan 23, 2013)

HertzHound said:


> If it’s a separate structure, it needs another ground rod. The structure could be a building or just a post in the ground with a panel on it. I’d have to look it up to see if the 25 ohms has to be proved again, or if just one rod is sufficient. I just put in two everywhere. At this point I would think it’s a auxiliary grounding electrode, so one would be sufficient? Kinda like some jobs want a ground rod at each light pole in a parking lot?


IMO the 25ohm rule is not worth measuring to save a ground rod. Just Hilti 2 into the ground and move on.


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## Adam B (Feb 13, 2021)

Thank you for all the feedback from everyone, I really appreciate it. The only other question I had was are the disconnecting means required even if the SEU cable terminates within 5' of entering the home? This was always the rule of thumb I went by with adding a disconnect into the setup, but wasn't sure if it's required because of not being separated by a firewall.

The pictures aren't the best quality, but here is a better setup of what I'm working with.


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## Dennis Alwon (May 9, 2009)

The disconnects need to be grouped. In the 2020 NEC they would need to be outside also.


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## Dennis Alwon (May 9, 2009)

The general rule is that the service conductors must terminate in a panel as near as possible to where the conductors enter the building. This is 2017 NEC



> 230.70 General. Means shall be provided to disconnect all
> conductors in a building or other structure from the service entrance
> conductors.
> (A) Location. The service disconnecting means shall be installed
> ...


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## kb1jb1 (Nov 11, 2017)

HertzHound said:


> To me all the service disconnects need to be at one location. So add three enclosed breakers under the meters. Add two ground rods near the trough, and run #6 to the trough. Run the water ground to the trough. Install a ground bar in the trough. Size the water ground to the service entrance conductors in the riser. Size the grounding electrode tap conductors by the size of the feeder taps to the meters.
> 
> Run SER to each apartment. At the garage you need to add another ground rod, and run that to the garage sub panel. The garage sub panel would also need a main breaker. The other two can be main lug.



This sounds the right way to do it. When I was an inspector, I saw many houses split for two or more meters with one MCB panel upstairs and one MCB panel downstairs. I kept telling the contractors that all disconnects have to be grouped together. That it is only a one family house with two living spaces. No fire wall. Nobody listens and they just went to another inspector. I gave up and went back on my own.


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## VELOCI3 (Aug 15, 2019)

The garage is fed free air from the load side of its utility meter from the main building using triplex? Quadplex will need to be used to maintain the neutral and ground separation. 

The main ground could be done with a single conductor if more convenient. Just get a bus bar to mount near the discos. 


Sent from my iPad using Tapatalk


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