Sizing GEC for outdoor dry-type xfmr

[wbalsam1]

iwire recently posted this on another thread and it got me to wondering something:

...Here a common power company requirement around pad mount transformers is four 3/4" x 10' ground rods at each corner of the pad, looped together with 4/0 bare cad welded to each rod with a 4/0 bare cad welded to the ring on each side running into the wiring compartment.

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Hers's my Q: How is the grounding electrode conductor sized for a primary transformer over 600 volts and a secondary of 120/240?
My only answer (so far) is Table 250.66 having to do with the size of the derived phase conductors of the SDS.
Help, please. :smile:

 

[mdshunk]

They're rod electrodes, so you really don't need anything bigger than #6. Number 6 is about the smallest you're going to be able to cadweld easily without fusing it off too.

 

[Pierre C Belarge]

The primary side is their detail. The secondary side is their detail. What they want is what they usually get.

If the tranformer is private and the POCO is not involved, than it is sized accordingly to the NEC.