AC combiner box - Neutral to Groung Bond

[bryankloos]

Hey Guys,

I'm getting ready to wire up my system as roofing repair/work is coming to a completion and racking is about to go up.
I have 3 strings of 13 panels with Enphase S280s. Trunk cable penetrates the roof with a soladeck. Each string then goes to a dedicated AC combiner (Main lug panel) in the walk up attic. Then one larger gauge run to the AC disco and line side connection.

My questing is this. Trunk cable and rack grounds combine in the soladeck, Then, #8 ground, and each set of L1, L2 and N for the sub arrays run to the AC combiner. At the combiner, are ground and neutral to remain isolated as would be in a sub panel? Everything else seems pretty straight forward to me, or so I think.

Any help?

Thanks,

Bryan

[emartin00]

Yes, ground and neutral must remain separate until the main panel.
If you combine the ground and neutral, you end up with 2 possible fault paths, which would mean the OCPD would not trip.

[bryankloos]

Just as I thought, as is the same for any sub-panel... thanks for the clarification.
My single line diagram wasn't exactly clear (or I'm not exactly clear on interpreting it)

This said, as my grounds (inverter and racking) combine in the soladeck ground buss, I simply continue with one ground from the soladeck to the ac combiner panel (which is isolated from neutral), and also bring a L1, L2 and N from each string to the combiner. If so, I can use three conductor THWN-2 for each string and on #8 ground to the combiner. Right?

[emartin00]

#10 is adequate before the combiner, but you'll have to go up to #6 wire after the combiner. 13 panels at 1.13A each is 14.7A per string. 3 strings gives you 44.1A plus adding the 125% factor brings you just over 55A.

[bryankloos]

Soladeck to Combiner is spec'd at #10 THWN-2 and #8 EGC.
Combiner to disco and line connection is spec'd at #3 THWN-2 and #6 EGC per my engineering report. Probably due to run distance...