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Thread: NMFC (Seal tite, liquid tite) on roof

  1. #1
    Join Date
    Jan 2012
    Location
    CA
    Posts
    526

    NMFC (Seal tite, liquid tite) on roof

    Recent experience with extreme heat and UV radiation on roofs got me considering the suitability of flexible PVC conduit on a roof.
    aka NMFC

    For decades I have used EMT.

    Recently, am tempted to cut a length of NMFC as a sleeve for PV Wire or Micro-inverter cabling between arrays. As a jumper.
    No connectors are needed at ends, no bending, no grounding bushings......you get it.....big labor saver.

    However,
    I know enough to know "sunlight resistant" in the product description doesn't mean much in a PV application, for 30 years, on a roof.

    I am curious what people think.

  2. #2
    Join Date
    Jun 2004
    Location
    Cherry Valley NY, Seattle, WA
    Posts
    4,531
    Quote Originally Posted by Zee View Post
    Recent experience with extreme heat and UV radiation on roofs got me considering the suitability of flexible PVC conduit on a roof.
    aka NMFC

    For decades I have used EMT.

    Recently, am tempted to cut a length of NMFC as a sleeve for PV Wire or Micro-inverter cabling between arrays. As a jumper.
    No connectors are needed at ends, no bending, no grounding bushings......you get it.....big labor saver.

    However,
    I know enough to know "sunlight resistant" in the product description doesn't mean much in a PV application, for 30 years, on a roof.

    I am curious what people think.
    I think you mean LFNC. I hate that stuff more than anything in the world. Maybe even more than those new gas cans. I would use LFMC, it is a much better product.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  3. #3
    Join Date
    Feb 2005
    Location
    South of Bawstin
    Posts
    1,242
    Here is the UL info on LFNC...

    1 Scope


    1.1 These requirements cover liquid-tight flexible nonmetallic conduit in the 3/8 – 4 (12 – 103) trade sizes of Type LFNC-A (Layered), Type LFNC-B (Integral), and Type LFNC-C (Corrugated) constructions. The conduit is intended for installation in accordance with the National Electrical Code (NEC) and the Canadian Electrical Code (CEC), Part 1. The values in parentheses are metric trade designators of conduit.
    1.2 Conduit covered by this Standard is intended for use in wet, dry, or oily locations at a maximum of 60°C (140°F), unless otherwise marked. (See Clause 6.)
    1.3 Fittings for liquid-tight flexible nonmetallic conduit are covered in UL 514B or CSA C22.2 No. 18.3.

    Using a 60 degree C raceway limits the ampacity of the enclosed conductors. It also may be hotter than that on the rooftop.

  4. #4
    Join Date
    Sep 2004
    Location
    Vancouver, WA
    Posts
    702

    PVC vs TPU

    I work on airports and in power substations. In both locations, I have seen flexible PVC-coated conduit, installed outdoors, severely deteriorated due to UV degradation.

    In substations, where equipment is expensive, equipment lives are intended to be long, and outages for repairs costly, I have specified TPU-coated flexible conduit rather than PVC. The problem is that TPU costs 10x PVC. But, a $100 adder on a $500,000 piece of equipment is acceptable.

    In cases where I have had no choice and PVC-coated conduit is installed, on airports in particular, I have asked to have flexible corrugated PE pipe (drain line) split and wrapped around the PVC to act as a sacrificial UV shield of the PVC-coated conduit. I figure if the PE lasts 10 years and the PVC under it lasts another 10 years, we have gotten acceptable life from the installation.

    I think PVC-coated conduit, used outdoors, exposed to UV, is just going to be someones future maintenance headache. It would sure be nice if "UV resistant" meant more than just a few years.
    e^(i pi) = -1

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