Solar Q: roof J-box

[Almot]

Trying to figure out how to attach small 4x4x2 PVC J-box on the EPDM/plywood roof.

There will be a big hole in the bottom, where a pair of #4 cables will go into the trailer. With a hole that big it would make sense fastening the box in the hole, rather than driving a few tapping screws through the box bottom.

I thought of Steel Conduit nipple - it goes through the hole, two bushings on the ends will hold the box to 3/8" plywood. To accommodate a pair of #4 cables, ID has to be 0.9-1.0", so nipple Trade Size 1" should work. Canadian Home Depot don't have it, only brass nipples in plumbing isle, I think it's a wrong stuff.

Checked the "List" of completed solar projects here - not much help. Some photos show Liquidtight plastic conduit fitting in that bottom hole. I don't mind using plastic fitting, less chances to short something in the box. But they have a short thread, about 1/2", this isn't going to work with 5/8" total of plywood, PVC, and EPDM. Or am I missing something here?

[Almot]

wintersun wrote:
Every box I have seen is not fully waterproof when mounted horizontally, even the box from AMsolar.

I've put this statement to test, since it claims to provide protection against "hose-directed water and water entry during prolonged submersion". This is $8 box from Home Depot, with rubber gasket - 1st link in the 1st post. IP code suggests duration from 5 minutes for spraying and 30 minutes for immersion. I'm not that patient. Filled the sink with water, tightened the box lid and held the box under water for 20 seconds. Opened again - not a drop inside. Since my roof will not be "immersed", I can make a plastic or neoprene hood over that lid, in case of some VERY heavy rain storm. So water ingress through the box lid does not worry me.

wintersun wrote:
With my setup I could see that there was 1/2" thick particle board before I made the hole for the cables. I avoideded any kind of gland or nipple as it would have interfered with routing the cables inside the cabinet that was below the box. I did use waterproof glands with the 10-2 cables from the panels.

"Waterproof glands" are probably what they call "strain relief"? I am not an electrician, correct me if I'm wrong, but the glands like Liquidtight (last link in the 1st post) are not waterproof around the cable. They are only waterproof around the end of the conduit - if you use a conduit - and around the J-box wall.

[wintersun]

I put sealant between the C-box and the roof and used stainless fasteners and then added sealant inside the box as well. Every box I have seen is not fully waterproof when mounted horizontally, even the box from AMsolar.

With my setup I could see that there was 1/2" thick particle board before I made the hole for the cables. I avoideded any kind of gland or nipple as it would have interfered with routing the cables inside the cabinet that was below the box. I did use waterproof glands with the 10-2 cables from the panels.

[Almot]

big buford wrote:

renoman69 wrote:
Scroll down to about the 10th picture.

J-box install

I did the same

Correct me if I'm wrong - plastic bushing in that photo does not fasten the J-box to the roof. I see the bushing holding a piece of conduit to the box. The box itself is fastened to the roof by tapping screws - I see some. Renoman, those small lugs you also attached with tapping screws into the PVC and plywood?

[big_buford]

renoman69 wrote:
Scroll down to about the 10th picture.

J-box install

I did the same, except I cut an X in the roof membrane before I ran hole saw thru plywood. Then I laid membrane flaps back down and dicor everything up.

[bobsallyh]

I did basically the same thing. Hole in bottom of J-box with cables coming down thru an interior wall. Used Dicor for the adhesive on the bottom of the box and also as sealant. Believe me, it won't go anywhere. I abandon a J-box that I instated five years ago that is down the same way. Ain't going anywhere!

[renoman69]

Scroll down to about the 10th picture.

J-box install

[westend]

Your idea of attaching the box from the center hole is the best. A plastic nipple and two box fasteners should get it done. Check the irrigation Dept. at HD for the nipple. If you're pulling the wires down through conduit, you could just cut and glue.

I got lucky and was able to connect the Jbox to an exterior conduit that rests aside my new plastic window trim. The entry into the trailer is close to the controller and the rest of my 12v power.