We do the "400 amp service" also with 2 200 amp panels and a 320 amp meter base.
I seen some run 1 #4 to both panels for the water pipe ground. I have also been told you need to run 2 #4 (1 to each panel) or 1 1/0 to both panels. They said you had to add the conductor area together (2 3/0).
When I try the math I get
2 3/0=.2790x2=.4580
.4580 is just under to a 350 kmil (.4656)
So I would figure a #2 water pipe ground to both panels.
When they call ask for a #1 I am guessing they are figuring it:
400 amps=500 kmil = 1/0 ground
But that does not seem the corect way to figure it if you have 2 3/0.
250-66 Notes: 1. the equivalent size of the largest sum of the areas of the corisponding conductor set.
So my question is what is the corect way to figure a single ground with 1 service and 2 main panels and no parallels?
Tom
