Routing array wiring inside mtg rails?

I'm in the process of installing an 8 KW system on my residence, including 2 Xantrex XW-4548 inverters, 3 XW-MPPT 150 controllers, and 46 SunTech 175 watt modules (among other things).

As soon as the snow gets off the roof I'm going to mount the modules on Pro-Solar XD RoofTrak rails, which are basically U-shaped aluminum extrusions about 3 inches high. The open side of the U faces up. My question is this: is it good practice (or even acceptable practice) to route the USE-2 wiring from the modules to the combiner boxes inside the U- channel of the mounting rails?

The combiner boxes are going to be bolted to the same rails as the modules; I'm just going to extend the length of the rails a couple of feet beyond the last module, so the wiring could come out of the channel and directly into the combiner box. This would provide mechanical protection for the wiring and also keep it out of the sun.

I realize that I'll have to get the local inspector to approve whatever I do, but I wondered what you professional installers thought of the idea. Has anyone ever done this? Is this common practice? I would basically be using the mounting rail as a raceway, but it would be an open top (exposed somewhat to the weather) raceway, although mostly covered by the modules. Since USE-2 is rated for wet locations I would think this would be okay, but I am a novice at this.

Any advice?


  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Routing array wiring inside mtg rails?

    Inspector should not allow it, where the L brackets lag into the U channel you will have the end of the bolts facing into the U channel ( assuming the accessories work like unirack stuff ) , if your packing wire in that channel, the you can have abrasion at those points. Also, if its a solid U channel, submerging the wire isn't a good idea when it rains
  • System2
    System2 Posts: 6,290 admin
    Re: Routing array wiring inside mtg rails?

    Thanks for the reply- The mounting feet I'm planning on using are the ProSolar "TileTrak" feet that have a 1/2" stud that protrudes through the bottom web of the rail with a hex nut on top and bottom of the rail, so there's not a pointed screw or lag bolt protruding into the channel, but there's definitely some stuff in the way.
    Also, the U-channel has a lip at the open top of the U that's rolled toward the inside. (Think Uni-Strut) The module mounting clamps are held to the rail with bolts that go into Tee nuts that catch the underside of those lips and clamp everything together, so the length of the clamp bolts would have to be kept short so the ends of the bolts didn't pinch the wire. Do-able, but it would take some care.
    Maybe I'll just strap the wires along the outside of the rails.
  • newenergy
    newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Routing array wiring inside mtg rails?

    I don't know if it's perfect, but it's really really unlikely the inspector will have a problem with it. I've done essentially the same where you have an array that has a small gap for some obstacle. I drilled some weep holes.

    It's definitely standard practice with prosolar to put the wire in the channel under the panels, but the bit sticking outside the array is not exactly typical.

    The thing to really watch out for is how you get out of the channel. If you are doing it for the wiring under the array you don't go across any sharp edges, but wherever you cut the rail there is a sharp edge.

    If there's a bolt in there that you really don't want to hit you could drill a hole and use a zip tie in that spot.