Running PV wires in an attic/indoors/basement guidelines?

[Cptx]

I’m interpreting guidelines that DC PV cable from panel array should be run in metal conduit or flexible metal conduit when inside the home/attic/basement.

The following is my plan. Please point out any errors in my interpretation of guidelines and offer any suggestions.
Thank you.

Six 400W panels on south side roof in a series then two 12AWG PV cables + array mount 6gauge copper grounding wire initially through 3/4 inch PVC conduit through the roof….then junction to 3/4 inch flexible metal conduit in the attic (copper grounding wire splits off at the junction to house ground across the attic then down the garage wall)…The DC PV cables then run out of house via soffit/eaves inside flexible metal conduit on the north side of the house to DC disconnect box then short run 3/4 inch PVC conduit to 20 Amp circuit breaker then short run of 3/4 inch PVC conduit to EG4 12K mini split outdoor unit.

 

[Zapper77]

I’m interpreting guidelines that DC PV cable from panel array should be run in metal conduit or flexible metal conduit when inside the home/attic/basement.

The following is my plan. Please point out any errors in my interpretation of guidelines and offer any suggestions.
Thank you.

Six 400W panels on south side roof in a series then two 12AWG PV cables + array mount 6gauge copper grounding wire initially through 3/4 inch PVC conduit through the roof….then junction to 3/4 inch flexible metal conduit in the attic (copper grounding wire splits off at the junction to house ground across the attic then down the garage wall)…The DC PV cables then run out of house via soffit/eaves inside flexible metal conduit on the north side of the house to DC disconnect box then short run 3/4 inch PVC conduit to 20 Amp circuit breaker then short run of 3/4 inch PVC conduit to EG4 12K mini split outdoor unit.

Do you plan on following NEC?

- May need 10 AWG not 12 per NEC
- Shouldn't be an issue but 500v DC max on/in residential
- Correct metal conduit
- If you can avoid the attic...the heat is a pain when accounting for derating
- Rapid Shutdown at the panel

If NEC doesn't apply....looks good to me...I'm no expert.

 

[Quattrohead]

I am currently asking the same question to Greenlancer. Planning on using 10 AWG MC 90 degree in the attic between the panel junction box and inverter.
Ground wire has to be 6 AWG on the roof but should be OK using the internal 10 AWG in the MC.
Will find out soon.

 

[Cptx]

Thank you for the feedback; I was unaware regarding the 10awg requirement in solar DC PV cables while running through the house. Easy change to my purchasing list.

The only way I could avoid the attic would be to run the wires off the roof, over the gutters and then pvc conduit all the way around to the north side in 3/4 pvc conduit. I actually like this idea a lot as cosmetics/aesthetics are low on my goal/appreciation list. I know my wife thinks otherwise and I would worry more about squirrels and wiring shenanigans going this route.

Thanks again.

 

[Cptx]

Would two 10awg Dc PV cables fit/run better in 1 inch conduit or is 3/4 inch conduit fine? I will guess inch would be easier for fishing the line through.

 

[Zapper77]

Would two 10awg Dc PV cables fit/run better in 1 inch conduit or is 3/4 inch conduit fine? I will guess inch would be easier for fishing the line through.

1" for future expansion

 

[Quattrohead]

PVC conduit will always end up breaking down in the sun, especially southern states.
I was up on a commercial roof the other week, shattered pieces of PVC conduit everywhere with wires showing.
Some of the wire did not look good either, reminded me of the knob and tube problems.

 

[Cptx]

Yes, I was thinking of spraying or painting everything with that rubberized undercoating….or is there something better?

 

[Solar Guppy]

You should use a listed transition box to meet code. This is what I used, the transition is emt and then connects inside that attic to BX cable aka armored metal clad cable.

 

[Cptx]

As I’m not using any micro inverters, I will guess that I can just plug two 10 AWG PV cables into that transition box and run the 6 gauge copper ground wire through it.

 

[Solar Guppy]

Yes. your question was about building codes, the enphase in the picture has nothing to do with the transition from roof to inside the premise. You can't use PVC as a transition as you had mentioned, it has to be metallic and UL listed for the application.

 

[Cptx]

Thank you, always nice to be in compliance.
So junction boxes like these receive MC4 connections and then output BX cable through the roof.

Guess I’ll need another similar junction box on the other side of the house to go back to PV as that is what the solar DC disconnnect, Circuit breaker, and mini split accept.

 

[Bluedog225]

Metal conduit to a pull box on the roof. Then a couple of wires exiting the bottom of the pull box, forming a drip loop, then into a solar cable gland box on the soffit. Pretty inconspicuous and easy on the eyes.

 

[zanydroid]

You don't have to use MC4 connectors for those transition boxes, you can also directly clamp onto the PV cable with glands and then terminate the MC4 on, EG, insulated DIN terminal blocks. Those transition boxes tend to come with pre-installed DIN rails for this purpose.

THHN should be easier to pull.

I don't know that there's a rule saying you have to use #10 (in fact they make #12 PV, I welcome a code reference though), however if you look at the ampacity calculations #12 is rather restrictive wrt current. For instance if you end up having to swap your system to the new 56/112 style of panels (13A ISC) you're out of capacity since 13 * 1.56 > 20A. While DC gives you a large margin.

You should probably buy a generic MC4 crimper (like, not the $250 one) and authentic MC4 connectors (since MC4 connectors are known to be a fire risk, code even requires you to have connectors that are listed for use with each other. That means same brand or cross brand where one brand has a certificate saying that their connectors are cross tested with the other brand by UL or other lab.

If you are driving string voltage above 400-450V I'm not sure if THHN (600V working voltage limit) is legal to use since there are several effects that push up a DC string's working voltage (eg transformerless topology might add to the AC working voltage, low ambient temperature would definitely boost the DC voltage). If someone can explain whether this is correct/not correct I would appreciate it.

 

[zanydroid]

PVC has been dunked on plenty, but I just wanted to add that flex PVC is even worse, partly because it has a lower temperature rating than solid PVC when wet. That may make a difference for short circuits (there's an exemption for longer runs).

 

[pvgirl]

Guess I’ll need another similar junction box on the other side of the house to go back to PV as that is what the solar DC disconnnect, Circuit breaker, and mini split accept.

Single conductor PV wire is only permitted to be used within the pv array(NEC 2020 690.31(C)(1)) outside the PV array you will need to use any NEC allowed wiring method, mostly likely wire in some type of conduit. You may need different disconnect and breakers, espically if they are not listed.

 

[zanydroid]

Single conductor PV wire is only permitted to be used within the pv array(NEC 2020 690.31(C)(1)) outside the PV array you will need to use any NEC allowed wiring method, mostly likely wire in some type of conduit. You may need different disconnect and breakers, espically if they are not listed.

Isn’t PV wire in conduit, with +/- paired together and running with EGC (not sure if there’s a DC exemption but surely this is anyway the cheapest/fastest way) an approved wiring method?

I think what you are referring to is how you can just have PV wire hangout by itself with no pairing and just cable ties/clips holding it to support. IE much more relaxed than elsewhere.

 

[pvgirl]

Isn’t PV wire in conduit, with +/- paired together and running with EGC (not sure if there’s a DC exemption but surely this is anyway the cheapest/fastest way) an approved wiring method?

I think what you are referring to is how you can just have PV wire hangout by itself with no pairing and just cable ties/clips holding it to support. IE much more relaxed than elsewhere.

Yes in conduit it's fine but In the post I was responding to me sounds like they want to go back to single pv wires outside of conduit to connect devices that have mc4 type connectors on them.

 

[zanydroid]

Yes in conduit it's fine but In the post I was responding to me sounds like they want to go back to single pv wires outside of conduit to connect devices that have mc4 type connectors on them.

Right in that case they should buy disconnect boxes that come without MC4 and instead have either conduit fittings pre installed or have no fittings and you drill out holes for those fittings to go into.

 

[Cptx]

Thank you all for the feedback.
Other than the panels and mounting hardware, this is my initial list.