Multiple transformers

[hhsting]

I have ground ring encircling structure that is the nearest electrode. Multiple separately derived systems have GEC to grounding ring.

Ground ring is sized 4/0 AWG. I have 45 kva new transformer secondary conductor size is 4#1, 1#6 gnd.

So the question is conductor from 45 kva transformer to the ground ring I guess grounding electrode conductor should it be #4/0 AWG or #6?

 

[infinity]

Table 250.66 Note a.

 

[hhsting]

Table 250.66 Note a.

Right but since ground ring is involved sizing GEC to ground ring can’t be smaller than 4/0 since Ground ring is 4/0awg. But then do separately derived rules and table 250.66 it would be #6. So it’s confusing which one? No?

 

[tom baker]

Your GEC to the GR is sized per 250.30 (5), which leads to 250.66 part C is connection to ground ring, I would agree its a 4/0.
4/0 is a really large ground ring, smallest allowed is 2 AWG, did the copper development association have anything to do with the size?

 

[infinity]

Right but since ground ring is involved sizing GEC to ground ring can’t be smaller than 4/0 since Ground ring is 4/0awg. But then do separately derived rules and table 250.66 it would be #6. So it’s confusing which one? No?

Where does it say that? 250.66 says via 250.30(A)(5) to size the GEC according to the derived conductors, 250.68(C) says that the GEC is not required to be larger than the ground ring conductor.

250.68(C) Connections to Ground Rings. If the grounding electrode conductor or bonding jumper connected to a ground ring, as
described in 250.52(A)(4), does not extend on to other types of electrodes that require a larger size of conductor, the grounding electrode conductor shall not be required to be larger than the conductor used for the ground ring.