Rooftop junction box?

[dsalad]

Hopefully easy question, I tried searching up and down and couldn't find answer.

What junction box can I use on the roof to transition from PV wire to THWN-2? I plan to mount it to a rail and transition to 3/4 EMT conduit. Can I just use a watertight metal box from Home Depot? I saw someone here used the Wiley Ace-20 (cheapest I can find is $130!). What should I use? Oh...and can I just use the proper sized wire nuts in that enclosure? Is there any special requirement to do anything else than wire nuts and grounding?

Thank you!
Rich

[dsalad]

Aha... Part of my question answered: "a polaris wire connector would be used to connect wires in the inexpensive junction box with no terminals. Common wire nuts are not rated to withstand high heat and may melt, causing a short, so they should never be used for a rooftop solar array."

So it seems like I would get a cheap weatherproof enclosure from Home Depot and use these Polaris connectors... Scream out loud if this is wrong. Thank you!

[B-17]

A SolaDeck or a MidNite Solar Combiner

[dsalad]

Thanks. The soladeck doesn't work with flat concrete tiles (I couldn't figure out how to make it work). The MidNite combiner is interesting, but how do I mount it? Do I need all that fanciness for making a simple PV to THWN-2 junction? And...looks to be $77 each. Kinda pricey.

[B-17]

You could use a 6"x6" PVC box with two of the MidNite Short Bus Bars inside. One in black and the other one in white or red. With the watertight glands or strain reliefs it will likely add up to ~50% of what a MidNite combine costs. If you are combining strings then the MidNite combiner should be used anyway. No combining being done?

[dsalad]

No combining. Will have three arrays feeding one inverter outside the house. Just need to transition to THWN-2 wire on roof. Thanks for the advice!

[B-17]

Then you will want a total of four or six Bus Bars and a box big enough

[Matrix]

How big is the Array? Are you trying to use if for a Rapid Shutdown system to comply with code?

[dsalad]

Hi... I have 26 panels of 315W each (~8190W). Splitting it into 3 strings (10 + 8 + 8). The panels will be in 4 different locations on the roof (10 West facing, 16 East facing). My plan is to transition from PV wire to THWN-2 on the roof, drop the conduit into the attic and then down to the inverter (SMA SUNNY BOY SB 7.0-US 7KW STRING INVERTER W/ SPS 3 MPPT which has a DC disconnect). I don't have plans for a rapid disconnect (that I know of)...should I?

[ButchDeal]

Hi... I have 26 panels of 315W each (~8190W). Splitting it into 3 strings (10 + 8 + 8). The panels will be in 4 different locations on the roof (10 West facing, 16 East facing). My plan is to transition from PV wire to THWN-2 on the roof, drop the conduit into the attic and then down to the inverter (SMA SUNNY BOY SB 7.0-US 7KW STRING INVERTER W/ SPS 3 MPPT which has a DC disconnect). I don't have plans for a rapid disconnect (that I know of)...should I?

does your AHJ require a rapid disconnect? if so you will need two of them and a rapid shutdown controller. Or you could combine the 16 east facing into a single string and use one rapid shutdown device (each can control two strings).

If you have not ordered your inverter a better solution would be co convert to solaredge which has rapid shutdown integrated.

[dsalad]

Thank you!

[library]

I initially planned something similar to you, dsalad, a standard string setup with Sunny boy. I had to move to solaredge for the rapid shutdown requirement and now with a defective panel (about 60% of what it should be outputting) I'm *really* glad I did. Otherwise it would have been days on the roof swapping panels to find the bad one. Well worth the extra money for the panel level monitoring.

Now if I had a ground mount system it wouldn't be an issue. No roof in the way while you rewire things. As a guy who has roofed a number of houses playing with solar panels on the roof is pretty miserable.

[SunEagle]

I initially planned something similar to you, dsalad, a standard string setup with Sunny boy. I had to move to solaredge for the rapid shutdown requirement and now with a defective panel (about 60% of what it should be outputting) I'm *really* glad I did. Otherwise it would have been days on the roof swapping panels to find the bad one. Well worth the extra money for the panel level monitoring.

Now if I had a ground mount system it wouldn't be an issue. No roof in the way while you rewire things. As a guy who has roofed a number of houses playing with solar panels on the roof is pretty miserable.

As the saying goes, "it isn't the fall that hurts you...it is the sudden stop at the bottom".