Grounding and Bonding a Solar System Arrays

[harborrick]

I need help on a few items.I am new to Solar.
I have a carport style arrays and have two Combiner Boxes both spread apart on 2 different columns.
I also have 2 more arrays with 1 CB box each.
We have 2 Inverters about 200 feet away on a pad. 75kw and 100kw
At CB columns I have driven a ground rod and bonded them with a #6 to Column and to CB box ground buss
From CB I have run my equipment ground back to Inverter.#8 in size to nec code.
At Inverter I have installed 1 ground rod and installed a new GEC to main service sizing wire same size as existing ground of main service (Example ,existing service 600 amp GEC 2/0 cu)
My questions is do I need to carry GEC all the way to arrays?
If so does it have to be same as service GEC
I have seen it drawn different ways from different engineers.
Thanks in advance.

 

[jaggedben]

At CB columns I have driven a ground rod and bonded them with a #6 to Column and to CB box ground buss

If you are on the 2008 NEC (or the 2010 California Electric Code) this is required, so you did good. (If you are on any code before or after, it's not actually required, although it might increase protection against surges from lightning, and I've always seen it done as a matter of course on systems this size.)

From CB I have run my equipment ground back to Inverter.#8 in size to nec code.

Hmm. That sounds like it is probably too small for an EGC for this run in a system of this size. See 690.45. #8 would probably be fine for the EGC from the array to the combiner, but not for combiner to inverter.

At Inverter I have installed 1 ground rod and installed a new GEC to main service sizing wire same size as existing ground of main service (Example ,existing service 600 amp GEC 2/0 cu)

According to code, you probably didn't need to install that rod or size the GEC higher than the DC requirement, which would be equal to the largest conductor in the system. But again, it might afford some additional protection against lightning.

My questions is do I need to carry GEC all the way to arrays?

Technically no, but you do need bonding jumpers between the existing grounding electrode system and your new rods at the inverters and the arrays. So that amounts to about the same thing.

If so does it have to be same as service GEC

This could be open to interpretation. The strictest reading of the code the bonding jumper has to be equal to the larger of the following:
1) the existing AC GEC (according to the 2011 NEC) or table 250.66 (according to the 2010 CEC).
OR
2) the DC GEC requirement, which is the largest conductor fed by the system, which is presumably your PV output conductors from the combiner to the inverter.

You can also make an argument that you do not need any sole connection to a rod to be bigger than #6. That argument would be based on 250.66 (A) and 250.166 (C).

I have seen it drawn different ways from different engineers.

Yeah, there can be more than one correct way to do it, and I bet many AHJs do not consistently enforce the code.

...

Here's what would probably get you on the good side of the 2010 CEC:

-Install new grounding conductors between the combiners and the inverters, sized based on which ever of these is larger:
a)table 250.122 and the short-circuit current of the DC outputs from the combiners
b) the existing AC GEC size of 2/0 cu
-Terminate these conductors in the groundbars at the combiners and inverters at their respective ends.
-Run a #6 GEC from groundbars at the combiners and inverters to their respective rods. (You said you've already done this at the combiners, you weren't totally clear about it at the inverters.)

Of course the AHJ has the final say.