Originally Posted by TonyD
I respectfully disagree only because this transition is made for 10g cable.
I'm using a PVC junction box to combine all 10 gauge solar outputs into one 6 gauge wire. From this junction box the 10g twin wires go into another PVC sealed housing which has an opening on the bottom which goes against the roof.
the best solution is a PVC junction box and glands for the 10 GA PV wire. Enough room for more than one panel and room for buss bars to transition the 10 GA to 8 GA going down through the roof to the charge controller. You can buy glands for the 10 GA anywhere and they will fit the junction box.
In my opinion most of the commercial boxes built for this purpose are way overpriced at $70 or more. If you run pvc conduit through the roof and let it stick up 1/4" and seal it, the junction box should have an oversize hole that allows the PVC to penetrate. Seal the junction box down to the roof and you are all set.