GEC "Oddity"

[augie47]

It is fairly common in these parts for the E/Cs to use a 400 kcmil cu riser for a 400 amp residential service per 310.15(B)(6).
When they do so, they install a 1/0 GEC per 250.66
Today I had a job where the 400 amp service was fed by parallel 3/0 cu.
Per Table 8 3/0 is 167,800 x 2 = 335,600 which by 250.66 requires a #2 GEC.

 

[infinity]

Yup that discrepancy has been around forever. That is one reason why a question about what size GEC do I need for the water pipe for a 400 amp service is hard to answer without all of the information.

 

[Dennis Alwon]

I have mentioned this a number of times. If you have a 400 amp combo meter main that does not have service conductors, ie a busbar, then you need 1/0 to the GEC- Note 2 in art.250.66. If you use a 400 amp meter with 2- 200 amp panels using 3/0 copper then a #2 is all that is needed. Note 1 in art. 250.66