Ground Gauge on Solar Wiring Diagram

[brad14]

I'm planning a solar install for my house and received a wiring diagram from a solar company. I was wondering if someone could clarify as to why the ground is called out separately from the hot wires and why the gauge is different? After the junction box, the diagram calls out two sets of hot wires which I would wire with standard 10-2 ROMEX which includes a ground. For each junction box, there would be two 10-2 ROMEX cables and each one would contain a ground so there would be two #10 gauge ground conductors. I'm wondering if I can ignore the #8 gauge call out on the ground? Two #10 gauge grounds from the ROMEX equals about a #7 gauge wire so it seems like I'd be covered. If that's the case then I'm curious why that wasn't labeled as (2) #10 AWG CU GND THWN and why it called out #8 separately.

As a separate question, I'm going to be running the circuits to the solar array through the attic and then down an interior finished wall until I get to the basement. Would it be recommended to use MC cable since I won't be able support the cable inside the wall? From what I can tell from the NEC, I can run MC cable a few feet longer without support and it obviously protects the conductors better.

Thanks.

 

[FionaZuppa]

What #8 ?

 

[brad14]

What #8 ?

It's saying 8 gauge wire. I think I have this squared away. I think the manner in which it's drawn is confusing to me. Each set of hots will have their own ground that would be 10 gauge. Those combined would equal something on the order of a 7 gauge wire along with the MC conduit is even more grounding. I'm guessing it's written like that incase it were to be run with individual conductors instead of buying ROMEX or MC cable that comes prepackaged with a ground for each set of hots.

 

[ggunn]

It's saying 8 gauge wire. I think I have this squared away. I think the manner in which it's drawn is confusing to me. Each set of hots will have their own ground that would be 10 gauge. Those combined would equal something on the order of a 7 gauge wire along with the MC conduit is even more grounding. I'm guessing it's written like that incase it were to be run with individual conductors instead of buying ROMEX or MC cable that comes prepackaged with a ground for each set of hots.

I'm not sure what you are dealing with, but when multiple circuits are in a conduit together the EGC need only be as big as what is required by the largest circuit in the conduit. Also, there is no AWG #7 wire; AWG #3 is the smallest odd number gauge..

 

[brad14]

So after twisting myself in knots trying to explain the callout for #8 gauge wire. I heard back from the electrical designer and it turns out it's just a mistake, they changed it to #10 to match the hot conductors. I guess that answers that question.