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  • Penetration into roof via junction box?

    Hi guys,
    I have almost all aspects of my off-grid solar install figured out now. I'm building an enclosed "closet" to mount on the back of the cabin to put the batteries and electronics in (separated and vented the battery compartment) and now I'm trying to figure out the actual wiring portion.

    I have a new tin roof I'm mounting everything on, and so I would like to find a good way to penetrated into the attic space, and then run the PV wiring over to the edge of the house, down the inside of the wall, and pop out the wall inside the electronics enclosure to connect to the charge controller.

    My current idea is to drill a 1" hole in the roof, and run an armored cable (like AC90 but in Canada we have Teck90 which is stranded and armored with waterproofing and burial ratings) through the structure up to the whole. I'll use a cable connector to enter the armored cable into the PVC box and then use waterproof glands to enter the Panel's PVU cabling into the same PVC box. Splice cables together, and silicone seal the box to the roof (therefor covering the whole I made for the cabling). my racking sits about 3" about the roof, and the PVC box I have is about 2.5" tall so I'm aiming to put the box below the panels to help minimize sun exposure and help minimize potential for water ingress...

    Does this sound like a good idea? What do you guys do?

    I didn't think it was a good idea to just run 30' of PVU cable through the ceiling and walls.... In fact I think it's against electrical codes here anyway...

  • #2
    Originally posted by Xplode View Post
    I didn't think it was a good idea to just run 30' of PVU cable through the ceiling and walls.... In fact I think it's against electrical codes here anyway...
    Well unless you are pulling a Permit and have an Inspections, then code is a grey area and not enforceable. Anyway has nothing to do with your application.

    I assume you are you are Canadian under CEC? If so I can tell you with 99% certainty there is nothing that would prevent you from running wire/cable in walls, attics, drop ceilings, or whatever space you want to use. Unless the area is wet or in classified Hazard you can run wire/cable. That is the default standard of how it is done. Ever been in new construction and see any wiring? No it is all kept out of sight safe and sound where it is not accessible exposed to dangers. I say 99% because I am in the USA and CEC mirrors NEC and lags a cycle behind us. Few minor differences but basically the same requirements.

    Not going to tell you how to wire your system, I do not care, but what I will tell you is running wires in walls and ceilings is perfectly fine and complies with codes. In fact highly desirable because it offers protection and looks better hidden. In other words it is an Option open to you, so you do not have to eliminate it based on code because it is code compliant to do so. Only catch is it must be separate from your AC power wiring and Visual Identification. Both conditions are easy to meet. Don't run with AC power wires/cables, and use different colored conductors except Black and White combination which is 120 VAC. Say red and Black. Where system wires must share same space like an Inverter or switch, each system shall be compartmentalized with a divider.
    MSEE, PE

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    • #3
      Hi Sunking - I'm a ticketed electrician, and yes you are correct about the CEC applying to me (although grey as you put it in this case :P). No I am not getting it inspected, but I am not allowed (under CEC) to run loose single conductor in the walls for anything other than ELV signal wiring. It is required by code to be run in a conduit or armored cable since it is a more fire-hazard type of energy than AC power. If the wire gets hit by someone hanging a picture or shelf, there are no roof top fuses to open and cut the current flow. I was also told that rule was added in conjunction with the birdhouse/Rapid Shut Down rules to protect firefighters and such... Well... no firefighters at my cabin so I'm not worried about them, but I do like to make the installation as bulletproof as possible on that front. I was originally going to run flex through the ceiling/wall and just pull a pre-made 40' #10 PVU cable set through but i can do it cheaper with teck90 cabling since I can probably get it for free from work.

      Sooo I suppose the question was more about the roof penetration than anything. I see gasketted PVC roof entries with built in glands, but since I want to transition to another cabling type (or metal raceway), I'm not sure about which method is best for sealing the physical penetration...



      Comment


      • #4
        Unless you have more than 2 parallel strings, there is no requirement for OCPD's as solar panels are current sources, not voltage.

        Example lets say you have two parallel strings using 12 AWG conductor, and each string Imp = 9 amps x 2 = 18 amps. What happens to a 12 AWG conductor with 18 amps flowing all all day shorted out?

        Nothing!

        Now if you were to drive that nail into 120 VAC voltage source like from the POCO and short it out and you have a FIRE instantly.
        MSEE, PE

        Comment


        • #5
          I think you are sorely mistaken on your statement that nothing will happen to that #12awg wire that has a nail through it. the nail is not a good quality splice and will heat up, start arcing, and show definite potential to be a fire hazard... the cable 20' away will not be hot since, but the actual nail puncture is definitely a problem.

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          • #6
            Originally posted by Xplode View Post
            I think you are sorely mistaken on your statement that nothing will happen to that #12awg wire that has a nail through it. the nail is not a good quality splice and will heat up, start arcing, and show definite potential to be a fire hazard... the cable 20' away will not be hot since, but the actual nail puncture is definitely a problem.
            There is a reason code does not require OCPD's for 2 strings or less.

            MSEE, PE

            Comment


            • #7
              I don't do a lot of solar work obviously, but i can't see anything in the CEC about 2 strings or less not needing OCPDs. Everything I read seems to indicate there needs to be protective devices, they need to be rated at 100% of the capacity of the panels (or next standard higher value), and that everything needs to be installed in metal raceways. There are rules about requiring DC Arc Fault protection as well.


              But again, the question I posed originally was more of a "what do you think of my method of penetrating the roof" and not so much a code argument.

              Comment


              • #8
                I think gluing a J-box to the roof is a poor idea. Something like a plumbing roof vent, real flashing, a weather head for the cables and then splice from the UV rated cable, to standard wiring , at a j-box in the attic, is what I'd do.
                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

                Comment


                • #9
                  Originally posted by Mike90250 View Post
                  I think gluing a J-box to the roof is a poor idea. Something like a plumbing roof vent, real flashing, a weather head for the cables and then splice from the UV rated cable, to standard wiring , at a j-box in the attic, is what I'd do.
                  Thanks for the feedback Mike... I hesitate to make a penetration in the roof under a jb, but is a plumbing roof vent any better? (the roof is metal, not shingles) I don't have an actual attic I can access once the ceiling is up inside (it's currently under construction).. But I could transition to the teck90 cabling (which is also UV rated) on the roof and then go down through a vent if that really does seem like the better idea...

                  Why do you prefer having to seal the vent, vs sealing the jb?

                  Comment


                  • #10
                    If I were to have to mount a J-box on the roof I would use a liberal amount of Butyl rubber sealant under the box followed by a clean bead around the perimeter with some quality urethane sealant. 3M 5200 comes to mind for the perimeter. Butyl rubber is interesting stuff. It never cures. It will stay soft and sticky indefinately. While nothing is forever this combo would remain sealed for a very long time.
                    Last edited by littleharbor; 07-20-2018, 08:01 AM.
                    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                    Comment


                    • #11
                      a j-box is not a usual device to seal a hole in a roof.
                      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                      solar: http://tinyurl.com/LMR-Solar
                      gen: http://tinyurl.com/LMR-Lister

                      Comment


                      • #12
                        Soladeck, whatever. Referring to the materials I'd use if I had to do this.
                        2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                        Comment


                        • #13
                          Originally posted by littleharbor View Post
                          Soladeck, whatever. Referring to the materials I'd use if I had to do this.
                          That is actually a cool looking product that would work very good on a shingle roof, which one of my cabins is, so I may investigate that further for that install.

                          But flashing and such doesn't work on a metal roof... Sigh... I really don't want it to leak, but I used some Geocel 4500 on a metal roof penetration at a factory a couple months ago and it seems to have worked awesome for bringing up power cabling to a motor on the roof. Bonds to metal and PVC, cures underwater and stays flexible... But in that case I built a ABS Pipe stack and sealed an EPDM style rubber boot around it... don't need a 3" pipe x 18" high this time tho... aiming for a little more subtle.

                          https://www.geocelusa.com/product/ge...nding-sealant/


                          The solar supply shop sells and recommends LePage Quad MAX for penetrations
                          http://www.lepage.ca/en/lepage-produ...-quad-max.html


                          Looks like these products should work well enough for sealing the box down...

                          Comment


                          • #14
                            Originally posted by littleharbor View Post
                            If I were to have to mount a J-box on the roof I would use a liberal amount of Butyl rubber sealant under the box followed by a clean bead around the perimeter with some quality urethane sealant. 3M 5200 comes to mind for the perimeter. Butyl rubber is interesting stuff. It never cures. It will stay soft and sticky indefinately. While nothing is forever this combo would remain sealed for a very long time.
                            This sounds reasonable to me.

                            I'd want it fastened tightly to the roof so there was minimal movement. Probably locknuts both above and below getting it tight as possible so that the jbox would not move much on that roof.


                            Another option is put the jbox on the rail for the solar module. And have a boot around the conduit.

                            Or don't do a jbox - just have a boot with the conduit going to a gland.

                            Comment


                            • #15
                              Originally posted by foo1bar View Post

                              This sounds reasonable to me.

                              I'd want it fastened tightly to the roof so there was minimal movement. Probably locknuts both above and below getting it tight as possible so that the jbox would not move much on that roof.


                              Another option is put the jbox on the rail for the solar module. And have a boot around the conduit.

                              Or don't do a jbox - just have a boot with the conduit going to a gland.

                              This isn't a bad idea either, except i have two things to bring down through the roof. a Teck90 cable (about 3/4-1" across) and a #6awg RW90 Ground wire. Not sure how to seal that nicely, unless I install a pipe and weatherhead type arrangement, but then I don't understand why that's a better solution than gluing down the jbox anyway... It's still a penetration of about the same size....

                              I think if I rotate the JB 45degrees so it's angled downstream of the roof, it'll help it not "catch" water, and it's under the panels so no direct driving rain or snow. Now I'm wondering if drilling a small 1/8" hole in the lower corner of the box will help ensure any water that does ingress won't fill up the box and end up in the cabin. I can use watertight connections on the cables entering the attic space so there is no way for water to leak through... All my cables entering the JB will be on the lower side again to prevent water ingress...

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