Multi-family Grounding Electrode Conductor Size

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sparky62298

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Milwaukee, WI
I own a 4 family unit that is in desparate need of a service upgrade. My plan is install 5 100A load centers (1 for each unit and 1 public panel for basement/stairway lights, furnace, washer/dryer, etc). A 5 position meter bank would be installed outside. The utility would supply 400 amps to the meter bank (120/240V, 3-wire, single phase). My question is what do I use to size the GEC and how large would it need to be? I'm not sure if I am to size it off of one panel or off of the 400A supplied by the utility.

Full disclosure: I'm a commercial electrician and I don't deal with residential work often, so I'm not real familiar with the codes that may apply to this multi-family unit.

Also, while I'm at it, can someone verify the 310.15(B)(6) applies to multi-family units (i.e. can I run #4AWG wire to each unit's individual 100A service panel)?

Thanks in advance for your opinions and comments.
 
You can actually do a few things with the gec depending on the water supplies being connected or not. If each unit has it's own water supply then I would run individual runs to the water in each unit from each disconnect. You can also do ths if the water lines are metallically connected but in that case I would probably run one gec from the meter based on a 250.66 note 1, or 2 -- I don't have my book .

T310.15(B)(6) would apply to each unit but not for the calculated load of all the units.
 
To add some information to this scenario, there is only one water main for the building and it is shared by all four units. All plumbing piping throughout the building is copper. So the way I see it, I would need to run 1 GEC from the meter bank to the water main. Then I was planning on tapping the GEC to each of the five panels. I would also tap the GEC to hit the two ground rods that are required in this state. I hope that adds something to the discussion.
 
Dennis Alwon said:
You can actually do a few things with the gec depending on the water supplies being connected or not. If each unit has it's own water supply then I would run individual runs to the water in each unit from each disconnect. You can also do ths if the water lines are metallically connected but in that case I would probably run one gec from the meter based on a 250.66 note 1, or 2 -- I don't have my book .

T310.15(B)(6) would apply to each unit but not for the calculated load of all the units.
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The way I figure that would be the sum of the areas of the SE conductors for each of the 5 panels. That appears to be 4/0, in which that would require #2AWG GEC according to Table 250.66. That sound about right?
 
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