Help with system wiring

[ElGranadaCa]

Greetings!

I'm new to this forum and I am hoping someone might give me some guidance. Here's my situation. I'm trying to configure and install solar into our house, which was built 17 years ago. At that time the builder installed 'fastjack' rooftop stanchions for solar panels and they pulled 3/4 electric PVC from the roof to the garage. That PVC is split in the attic with a T junction - which leads to two separate branches going through the roof via downpipes. (1 downpipe on the east and one on the west end) I plan to put a junction box on those down pipes.

I' can fit a total of 14 ea. REC410AA Pure panels with EnphaseEnergyInc. IQ8PLUS-72-M-US micro inverters and given the layout, I can balance it out to have 7 panels per branch circuit. The total length from the rooftop downpipe to the garage is roughly 60 ft. EACH.

Here is where I need help with the wire size and how many wires I need to pull through this single conduit.

The amperage per branch 410W per panel * 7 panels / 240 V = 6.52A. With 14 panels that is a max of 13A.

I believe I will need to pull a black and red - line with a bare copper ground (3 leads) to each junction box / branch circuit. to the 'combiner' ... 6 wires in total
Is that correct?

Given the amperage rating per branch, do I go with 10 /12 or 14 AWG? I've heard a few people tell me I need 10AWG - regardless - but that seems like huge overkill
and will not be fun pulling 6 across 60 ft of 3/4 in PVC.

Thanks in advance !

Good regards

Marty

 

[sumpower]

El Granada California, I would use #10 copper thhn/thwn. With the derating required for conductors on a roof for temperature compensation.

 

[timselectric]

I would use #10, also.
Due to the hot environment and conductor count.

I believe I will need to pull a black and red - line with a bare copper ground (3 leads) to each junction box / branch circuit. to the 'combiner' ... 6 wires in total
Is that correct?

You only need one ground conductor in a conduit.
So, 5 total.

 

[robbob2112]

One question for Tim - Can't you downsize the ground wire size by one?

The other thing that strikes me is you mentioned PVC for the conduit. If it is on the roof, in the attic, or attached to the house it needs to all be metal including the junction boxes. If you get a short or a melted wire it needs to be contained.

 

[timselectric]

One question for Tim - Can't you downsize the ground wire size by one?

No
I think you are referring to neutral downsizing. (On split-phase systems)

The other thing that strikes me is you mentioned PVC for the conduit. If it is on the roof, in the attic, or attached to the house it needs to all be metal including the junction boxes. If you get a short or a melted wire it needs to be contained.

This is AC wiring. (Micro inverters)
So as long as PVC is acceptable for the location, it's fine.

 

[robbob2112]

No
I think you are referring to neutral downsizing. (On split-phase systems)

This is AC wiring. (Micro inverters)
So as long as PVC is acceptable for the location, it's fine.

AH, I missed the microinverters.

 

[ElGranadaCa]

Hi. So I cap and split the ground to the 2 branches at the T? And pvc iscjust in attic and basement. I agree the rooftop conduit must be metal .