Conduit Size and Fill Recomendations

[NVCYberPro]

Hi I am looking for suggestions and tips with my conduit run as I will be moving my arrays to their permanent home and wiring.

My runs are going to be ~125 underground, then another +/- ~100' along the base of the house (under the deck etc).

From past recommendations we have settled on running 10 awg THHN from the DC solar disconnect to the inverters. I plan to pull wire for (2) arrays right now (4 x 10 awg) and plan to add another 2 arrays down the road for a total of 10 awg wires.

Questions: Do I need to run a ground back from the panel frames or simply ground those to a rod at the arrays?

What size conduit would be recommended that take the initial fill ( 4 x 10 awg) and allow for an easy pull of another 4 in a year or so?

I don't want to go to big and waste money, but I don't want to add more conduit later either.

All tips and suggestions appreciated.


BTW - How do you lay out a ground mount to face true south? I have a compass and know the declination but am at a loss on how to calculate the post locations.

 

[Hedges]

Definitely run a ground wire so you can bond PV panel frames to chassis of inverter or charge controller.

That protects against DC shock in case of a short at the array (including cracked panel and water).
It also protects against against AC shock; many AIO inverters couple AC onto PV wires, and there is capacitance to frame. Many stories of shocks on the forum.

I think ground wire ampacity is supposed to be 1.56 x sum of Isc for all PV strings.

Look up conduit fill table, then use significantly larger conduit. I am only able to reach allowed fill when stuffing wires through straight conduit, not pulling and not around bends.

Note that schedule 80 PVC has smaller ID than schedule 40 or rigid steel conduit.

Leave in at least a line to pull later wires, so you don't have to use fish tape. Maybe a wire, to use pulling additional wires. Or pull all planned wires at once.

Heavily bevel ID of conduit. I made the mistake of thinking factory cut square edges were OK, only reamed my cuts. The 90 degree edge bit in to insulation (or rather jacket; I was using it for LAN cable.)

 

[BentleyJ]

PVC conduit fill chart.

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According to the chart you could fit 9, #10 conductors in 3/4" sch 40. I wouldn't put that many in.

1" conduit minimum but keep in mind pulling in 4 more wires later on top of 5 that are already there is different than pulling all 9 at once. 1-1/4" would be a safer bet but its a trade off with price.

 

[ungrounded]

PVC conduit fill chart.

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According to the chart you could fit 9, #10 conductors in 3/4" sch 40. I wouldn't put that many in.

1" conduit minimum but keep in mind pulling in 4 more wires later on top of 5 that are already there is different than pulling all 9 at once. 1-1/4" would be a safer bet but its a trade off with price.

I agree with the 1"1/4. You want ease of pulling.

 

[GuyG]

pulling in 4 more wires later on top of 5 that are already there is different than pulling all 9 at once.

Yes. STRONGLY recommend pulling all at the same time. Also don’t forget to use plenty of lube and have a good friend to help feed and push at the other end.

 

[MarkSolar]

Look at XHHW instead on THWN, it's more flexible, tougher insulation and chemical resistant. It costs a bit more around here.

Aluminum wire will be about half the weight of copper so easier to pull, and about half the cost of copper.

 

[Tulex]

It's not that much more to oversize. That allows for easier pulling, and room to expand should there be a need.