250.66

[nec79]

I have a small commercial building that has 120/240 service drop coming to the back corner. I will have a 320 amp 2 position meter feeding 2 200 amp MBP's. 1 is directly behind meter and the other will be ran on exterior 50' to the other MBP. The water meter is located in the front of building. I've always had my disconnects built directly into the enclosure so there's no doubt size/where my GEC goes and where I come off for my rod. Question is how do I run my GEC from my water meter? Home run to each panel, to only 1, to 1 then interconnect the 2, use building steal as jumper? Ground rod at each panel? Any options and or answers greatly appreciated! 2014 NEC Thanks

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[augie47]

My first thought does not involve 250.66, but locally the install as you describe would not meet the requirements of 230.72, grouping of service disconnects.
More to your question: If POCO allows a meter connection I would connect my GECs to the grounded conductor in the meter.
If possible, I would follow 250.68(C) and connect my water to the structural steel.

 

[infinity]

I agree with Augie you'll need to group the two panels (service disconnects) in the same location. You can run individual GEC's from each panel to your electrodes or run a common GEC and tap off to each panel. If you have a building steel electrode you do not need to install ground rods

 

[augie47]

As Rob points out: 1 method

 

[Dennis Alwon]

Perhaps a bit off topic but this reminds me of how a grounding electrode conductor is sized by the service entrance conductors. Note 1 &2 are a part of that table and believe it or not it makes a difference in some situations.

When you have an install such as a 400 amp meter main combo unit the grounding electrode conductor will calculate to be 1/0 based on Note 2 of Table 250.66, but if you have 2- 200 amp panels as the op has and use either 4/0 or 250 Kcm the size of the grounding electrode conductor will only need to be #2. Now if you use 300 KCM then you will need 1/0 again.

I am making this point because I hear many contractors state that a 400 amp service needs a #2 and 200 needs a #4 grounding electrode conductor. While often true it is not always so and not dependent on the service size but the service conductor size.

 

[Dennis Alwon]

BTW, I agree with the others that your service disconnects must be grouped. Either install a 400 service disconnect or 2-200 amp discos near or adjacent to the meter