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GEC sizing on an apartment building with multiple POCO drops and panels.

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CaneCorso

Member
Location
Michigan
Occupation
Electrical Contractor
This is a strange apartment building. It is 1 building that has 3 overhead lines from the power company. Each of those lines is getting double tapped and feeding 2/0 SEU (aluminum) down to a group of meters.

The GEC has been sized according to 250.66 with 2/0 aluminum as the largest ungrounded conductor.. Which would make it a #6 CU GEC.

Inspector is saying sense each drop is tapped with qty. 2 - 2/0 SEU then the GEC should be sized for the equivalent area of qty. 2 - 2/0 AL. (or even larger as what will be discussed below.)

According to table 8, 2/0 is 67.43mm x2 = 134.86mm, making the equivalent conductor size 300kcm, requiring a GEC of #2 copper (or 1/0AL)

The answer should be in 250.64 (d)(1).

Typically I would be disagreeing with the inspector because to me it says size the GEC according to the largest conductor feeding the disconnect.

But my confusion is, there is already is an existing GEC ran. The existing GEC is 1 single unbroken #6cu from the water main and it is lugged onto each panel. As in this #6 is attached to possibly 12 panels.

Hopefully this crude drawing helps with understanding.
 

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C

CaneCorso

Member
Location
Michigan
Occupation
Electrical Contractor
I would need the solution to ground these. Wether this existing is correct or I'm running multiple #6 from each group of panel to the water main or 1 larger wire with irreversible splices. I'm open to suggestions as I have never seen this before and Mike's Illustrated Code book isn't as handy as it usually is!
 
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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
250.64(D) is fairly clear about this. You can run separate GECs from each disconnect to the electrodes, or tap to a common GEC. However, any portion that is common to multiple disconnects must be sized for the sum of the cross sectional area of the 2/0 conductors serving those disconnects.

So the single #6 cu going to all disconnects is not compliant. But six #6 cu, i.e one each going from each disconnect to the first electrode, would be compliant.

Alternatively you could tap a #6 from each disconnect to a common 2/0 GEC for all six and run that to the first electrode.

Btw it sounds like there are three services in violation of 230.2, but I don't think that really makes a difference to grounding requirements.
 
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