Looking for Suggestions for Transition or Pass-Thru Boxes

a0128958
a0128958 Solar Expert Posts: 316 ✭✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
I'm looking for suggestions for junction boxes used in roof-mounted PV systems, typically refereed to as transition or pass-thru boxes.

They're used as pass-thru boxes to transition from the USE-2 wires from the modules, to the THWN-2 wires that needs to be run in conduit inside the attic (no fuses, just wire connections inside the boxes).

What I'm referring to are low-profile transition boxes that are intended to mount directly on the roof.

These boxes are the 'life-line' between rain, and water getting inside the structure. The boxes need to be able to endure the harsh conditions found on roof tops. I'm thinking they need to be good for a good 25 years of leak proof ability.

There are NEMA 3 and 3R boxes, rated for outdoor use in limited orientations, and NEMA 4 and 4X boxes that have additional protection so the boxes can be mounted in any orientation, from vertical to horizontal.

My fundamental question is, what's used in the field that everyone agrees work well?

Many thanks!

Best regards,

Bill
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Comments

  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #2
    Re: Looking for Suggestions for Transition or Pass-Thru Boxes

    There is another thread here somewhere that discusses a few types of roof j-boxes.

    I personally, am not a fan of them. I don't like the idea of screwing a box down to the roof. I prefer to see a pipe coming up through the roof, with a properly sealed roof jack flashing, and then the j-box either bolted to the PV mounting rails, bolted to some other support or even bolted onto the top of the pipe.

    I'll see if I can search out that thread.
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #3
    Re: Looking for Suggestions for Transition or Pass-Thru Boxes

    Found something...not sure if it was what I was thinking of though. Anyway, here's a thread and solartek links to a product he likes:

    http://forum.solar-electric.com/showthread.php?t=5509&highlight=roof+junction

    The product is:

    http://www.rstcenterprises.com/pdf/soladeck_brochure.pdf


    Using the search tool here on the forums

    advanced search | keywords: roof and junction | show by post (at the bottom) not thread

    Will get you all the posts with both those keywords in them.

    EDIT: Duh...should have included the link to the search results as well. (No idea how long this link will actually work though.)

    http://forum.solar-electric.com/search.php?searchid=395733
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  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    #4
    Re: Looking for Suggestions for Transition or Pass-Thru Boxes

    Dhw, much appreciated.

    I did review the search list you provided - plenty of good learning resulted. Thanks.

    Summary of research, for help of others:

    1.) SolaDeck Flashed PV Roof-Mount Enclosure, Model SD 0783 ( http://www.rstcenterprises.com/pdf/soladeck_brochure.pdf ).
    NEMA-3R; steel with powder-coated finish; back-side conduit entry available.

    2.) ReadyWatt Medium Pass-Thru Wiring Box ( http://www.altestore.com/mmsolar/Others/pass_thru_box_Overview.pdf ).
    NEMA-4; requires conduit to come up through roof, with a sealed roof jack flashing, and connect to wiring box; box is mounted to panel rails, to top of pipe, or to some other support.

    3.) Penetrate through roof with conduit, with a sealed roof jack flashing, and an LB on the top of the piece of EMT, using raintight fittings, and put any desired junction box in attic for transition from USE-2 to THWN-2 wires (also allows for use of indoor-rated wirenuts)..

    4.) Wiley Electronics 'Acme Conduit Entry (ACE)' ( http://www.we-llc.com/PDF/acedata.pdf )
    NEMA-3R; back-side conduit entry available.

    My panels will be on top of the penetrations (regardless of style) (panels are 6" off of roof), and will thus provide some amount of protection from direct rain and direct UV. The penetrations will have forever exposure to water and ice.

    Many thanks.

    Best regards,

    Bill
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  • newenergy
    newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    #5
    Re: Looking for Suggestions for Transition or Pass-Thru Boxes

    I mostly run conduit through the roof and seal with a flashing - and then mount the jbox on the conduit or on the rail. I have used the Soladeck several times and it seems like a good waterproofing barrier - but I wouldn't generally use that if I weren't combining strings in there as well.

    If you're just transitioning, a PVC or metal nema3/4 box seems good to me. PVC is especially fine if it is shaded imo.
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #6
    Re: Looking for Suggestions for Transition or Pass-Thru Boxes

    In order of preference, I would choose:

    1. ReadyWatt
    2. Acme
    3. Soladeck


    That ReadyWatt looks literally bulletproof. I very much like that you can use standard (translation: easily replacable) fittings for the PV cable entry. It also has an easily replacable door gasket and a good pro-quality piano hinge. Another thing I like is that it has plenty of places to punch in additional holes if needed, and has lots of room inside to stuff the wiring. It does appear that it uses a key lock - I don't much like that - it should use standard screws (perhaps drilled for a safety wire) like any other electrical box. Maybe the key lock is a good idea for some situations, but for most it would just end up being a pain in the butt. However, it does have a nice lip around the door, so it wouldn't be a problem to drill and tap for screws in the field (and I probably would).

    The Acme appears to use some sort of formed plastic or rubber wire guide for the PV cable entry...GOOD LUCK getting a replacement for that piece 10 years from now when it's leaking water into your conduit. Also, if you look at the image where it's mounted on a pole top, those holes are pointed upward...I very much do not like (trust the weathertightness of) that arrangement. However, I did place it as #2 because it mounts up off the roof - but that is the ONLY reason it went at #2...really, for the most part I don't much like the look of that box.

    The Soladeck looks like quite a decent 18 ga. metal enclosure. My *only* problem with it is my inherent dislike of screwing boxes down to roofs - and that's not a problem with the product, just a personal preference.
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  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    #7
    Re: Looking for Suggestions for Transition or Pass-Thru Boxes

    Much appreciated, newenergy and dwh. Your comments, combined with the review of the search result threads, has provided a good educating thread on this subject.

    I do believe the ReadyWatt enclosure avoids using screws because they can easily rust such that they break off, 10 years later, when attempting to open the box, with as harsh as the conditions are up on the roof. Probably why it's a NEMA-4 and the other two are NEMA-3R.

    Many thanks.

    Best regards,

    Bill
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #8
    Re: Looking for Suggestions for Transition or Pass-Thru Boxes
    a0128958 wrote: »
    I do believe the ReadyWatt enclosure avoids using screws because they can easily rust such that they break off, 10 years later, when attempting to open the box, with as harsh as the conditions are up on the roof.

    Highly unlikely to happen IMHO. Take a look at any service entrance box - they have screws and they rarely, if ever, rust into place and break off. Even after decades.

    Here's a typical example (bottom of panel, left side):

    http://www.sunfrost.com/images/meters_outside.jpg

    And of course, if you use stainless steel screws...
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  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    #9
    Re: Looking for Suggestions for Transition or Pass-Thru Boxes

    I agree for equipment like you illustrate, which is typcially NEMA 3 or 3R rated.

    It's been my experience, that for wet location labeled equipment like switch boxes, the screws for the plates, like this: http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=17645241&PMT4NO=0 , if exposed to harsh conditions, will easily rust over and be very difficult to remove without breaking. (And the gasket seal will eventually fail depending on how severe the conditions are.)

    Thanks.

    Best regards,

    Bill
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #10
    Re: Looking for Suggestions for Transition or Pass-Thru Boxes
    a0128958 wrote: »
    I agree for equipment like you illustrate, which is typcially NEMA 3 or 3R rated.

    It's been my experience, that for wet location labeled equipment like switch boxes, the screws for the plates, like this: http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=17645241&PMT4NO=0 , if exposed to harsh conditions, will easily rust over and be very difficult to remove without breaking. (And the gasket seal will eventually fail depending on how severe the conditions are.)

    Thanks.

    Best regards,

    Bill

    Oh definitely. 6-32 non-stainless screwed into the drilled and tapped bosses (or the pot-metal brackets on the cheaper ones) of a typical "Bell Box" will absolutely rust and break off. This is why I (always) coat them with Led-Plate when I install them. Even after the box itself corrodes away, the screws will still come out.

    And yes, the gaskets are usually junk. I liked the older "tar paper" style MUCH better than the current "crap foam" style.
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