DC Passthrough Box in Attic to Consolidate 2 Strings Help

[proxybox]

Hi,

I currently have one string of panels connected with Solaredge Optimizers that lead to a junction box mounted on the racking and then transitions to THHN through EMT conduit mounted on the roof to the inverter.. Now, I want to install a Soladeck under a panel and route the wires through the attic. I also want to add a couple of more panels on a different roof plane and merge the two wire sets into a box but keep the strings separate and install them independently to each connection in the inverter.

Q1: What type of box would work? At first, I thought a simple 4x4 metal junction box but that doesn't seem right since I'll also need a ground bus or similar to combine the grounds. It's also probably too small for NEC and 6x 10 AWG wires and 2x 6 awg wires.

Q2: For the 6 awg ground wires, can I use grounding bushings for each leg of the EMT in the attic box and combine them in a ground bus bar and then lead one 6 awg wire to the inverter? I can make one ground wire continuous to the inverter but one will have to be 'spliced' in somehow so wanted to make sure this was ok for code.

Q3: Since I'm not combining the two strings into one, I don't need fuses/breakers like a string combiner has?

Sorry not an artist...

Thanks!


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[Mike 134]

I'll let the others comment on the string wiring but once you bring the wiring inside and go to EMT you can change the size to a #10 ground.

[SunEagle]

All I have to say is what does your AHJ think about the installation and have you gotten approval for this change?

[heimdm]

I would look at wago din-rail terminal blocks. Since you have 415v DC inside the house it has to all be metal or metal clad conduit and boxes. Solar Edge does like you combine strings together. If you have 2 strings you could combine those and run a single pair of wires down. Consult the SE docs on building a combiner box. However, I believe you said you want to keep them separate. On the grounding, for grounding usually it has to be unbroken ground wire to the ground rod. If it is for bonding then that is usually different. I am not electrician, so trying to remember from when I did my wiring.

[proxybox]

I would look at wago din-rail terminal blocks. Since you have 415v DC inside the house it has to all be metal or metal clad conduit and boxes. Solar Edge does like you combine strings together. If you have 2 strings you could combine those and run a single pair of wires down. Consult the SE docs on building a combiner box. However, I believe you said you want to keep them separate. On the grounding, for grounding usually it has to be unbroken ground wire to the ground rod. If it is for bonding then that is usually different. I am not electrician, so trying to remember from when I did my wiring.

Thanks! Appreciate your help.

415v? How did you calculate. Also, I'm getting some people who say plastic is ok in the attic. Is there a reference in the NEC for DC junctions needing to be metallic?

[Mike 134]

thanks! Appreciate your help.

415v? How did you calculate. Also, i'm getting some people who say plastic is ok in the attic. Is there a reference in the nec for dc junctions needing to be metallic?

2020 nec 690.31d