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Mains wiring question (USA)

Discussion in 'Misc Electronics' started by Bob E., Aug 17, 2010.

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  1. Bob E.

    Bob E. Guest

    A 1-story, flat-roof house (no basement) in California is going to be
    re-covered, so it's a prime time to do some electrical upgrades.

    The local building inspector says that romex cable run on the roof (before
    foam insulation is put on) must be covered by sheet metal stapled over it to
    protect from nail incursion (yes, he knows this is a *foam* roof, no
    shingles, etc., but no matter).

    I've asked electrical supply wholesalers about this but they have no product
    such as this.

    Is this something an electrical supplier would have? Or is just a roll of
    sheet metal stock what's called for?

    Thanks.
     
  2. Artemus

    Artemus Guest

    You might ask him how sheet metal, which staples can penetrate,
    will protect the romex from nails. The real requirement may be that
    you will need to run it in steel conduit.
    Art
     
  3. Bob E.

    Bob E. Guest

    You might ask him how sheet metal, which staples can penetrate,
    There is no logic to the declarations of building inspectors. He says if we
    choose to use romex (our option), we must cover it with metal strips wherever
    it is exposed.

    Another option is to use armored (MX) cable or EMT conduit. Romex seems the
    simplest if we can find a simple metal strap to cover it.

    Thanks.
     
  4. Bob E.

    Bob E. Guest

    YOU USUALLY COVER ROMEX/UF AND OTHER NON-METALLIC CABLES AT THE BEAMS
    On top of this flat-roofed building, picture a sea of plywood as far as the
    eye can see. Holes are drilled into the plywood where walls intersect the
    roof and romex is dropped into the walls. From this point to the distant
    location of the load (breaker) panel the romex is laid on the plywood and
    stapled down. Over this romex must be attached some kind of protection,
    declared by the local building inspector.

    Thanks.
     
  5. PeterD

    PeterD Guest

    Ah, that clarifies the one question I had (thought you were talking
    SE, not branch circuits...)

    I'd strongly recommend conduit (metalic) in this case. The sheet metal
    that would be required would be really hard to work with and form over
    the wires.

    Be careful that whatever route you go, you have the inspector's
    approval of the materials before you begin, you don't want the problem
    of "Oh, that metal is not heavy enough" to rear its ugly head after
    you've completed the task! 3
     
  6. Ecnerwal

    Ecnerwal Guest

    For actual protection you want EMT or armored cable. While this roof is
    a foam roof, there's no telling what the next roofing job (quite
    possibly not done by you) will put over it...

    To make the inspector happy you ask the inspector what the inspector
    wants to see. As described by you, a 50 foot roll (or as many as you
    need) of 4-6" aluminum flashing ("sheet metal") would apparently suit
    the inspector, while providing no protection to speak of (and the
    delightful possibility that you manage to staple into the cable while
    trying to staple the sheet metal over the cable). Of course, if you do
    that without getting a specific clearance from the inspector that this
    is what he wants to see, he might come back and indicate that he
    actually wanted galvanized steel, not aluminum, and make you rip it all
    up. At which point using EMT looks a whole lot easier, as well as more
    effective.
     
  7. bud--

    bud-- Guest

    Where some types of wiring is near the edge of a stud and may be hit by
    a drywall screw the wiring needs to be protected by a 1/16" steel plate.
    I suggest you ask the inspector how heavy the "sheet metal" has to be. I
    don't know of a standard electrical item for the protection you need. I
    would ask at a company that makes ventilating ducts.
     
  8. bud--

    bud-- Guest

    The steel plates you describe are what I was referring to. They are not
    required if the wiring is rigid metal conduit, IMC, rigid nonmetallic
    conduit or EMT. Rigid PVC would be cheaper than EMT. If you are using
    conduit, you should be fishing wires, not using it to protect Romex.
    With either Romex or fished wire, too many wires in the conduit requires
    derating the wire amp rating. Empty spares for future use may be useful,
    as you probably said. You may want conduits for cable, phone, ....

    This is an odd requirement and application. Run whatever you want to do
    past the inspector.
     
  9. GregS

    GregS Guest


    Seems like a nailing gun may penetrate conduit.

    greg
     
  10. Josepi

    Josepi Guest

    EMT (electrical metallic tubing) is not considered protection for wiring,
    just tubing.

    Use some square metal roof conduit designed for the job. It will probably
    stick up and not have anything stapled on top of it, Or put the wiring under
    the roof sheeting.


    For actual protection you want EMT or armored cable. While this roof is
    a foam roof, there's no telling what the next roofing job (quite
    possibly not done by you) will put over it...

    To make the inspector happy you ask the inspector what the inspector
    wants to see. As described by you, a 50 foot roll (or as many as you
    need) of 4-6" aluminum flashing ("sheet metal") would apparently suit
    the inspector, while providing no protection to speak of (and the
    delightful possibility that you manage to staple into the cable while
    trying to staple the sheet metal over the cable). Of course, if you do
    that without getting a specific clearance from the inspector that this
    is what he wants to see, he might come back and indicate that he
    actually wanted galvanized steel, not aluminum, and make you rip it all
    up. At which point using EMT looks a whole lot easier, as well as more
    effective.
     
  11. Charlie E.

    Charlie E. Guest

    You would buy the metal stock from the roofers. They use it to make
    up flashing and other transistions.

    Charlie
     
  12. Ken Lowe

    Ken Lowe Guest

    The inspector is not crazy, just following the arcane rules like the
    good droid he is. You're looking for something like these:

    http://www.garvinindustries.com/Ele...Cable-Protection/Cable-Protection-Plates/SP-3

    They are typically used to protect cables and copper water pipes from
    drywall nails/screws. Probably find them at the local mega hardware
    store for not much money -- 19 cents each at the link above.

    Like a few others, I'd vote for whatever type of conduit rocks your boat
    unless you're sure there will never again be the need for wiring mods.

    Ken
     
  13. Bob E.

    Bob E. Guest

    I'd strongly recommend conduit (metalic) in this case. The sheet metal
    The roofing contractor chimed in with an observation: conduit will result in
    the (poured? sprayed?) foam roof insulation making "mountain ranges" of foam
    which results in "pooling" when it rains, giving the roof the look of a lake
    district. Not a good thing. That's why low-profile romex (covered with
    protection) is the desired wiring method: good rain run-off.
    The inspector said it needs to be the same gauge as the "nail plates" that
    someone here mentioned (1/16" steel plate). That's going to be some heavy
    metal...

    Thanks.
     
  14. Guest

    A framing nailer might, but why are you using a framing nailer on a finished
    wall? OTOH, I highly doubt a finish nailer would penetrate conduit.
     
  15. Guest

    Huh? Wires *must* be stapled to the center of studs when run in wall
    cavities. They must be stapled with 6"(?) of plastic boxes. When run across
    the wall they go through holes drilled in the center of the stud, which is
    pretty much the same thing.
    No, that's for protection of the WIRE.
    Nope. NM is stapled to the studs or run in holes drilled in them. NM can be
    fished into wall cavities *after* the wall is finished but before the wall is
    finished it's stapled to the studs.
     
  16. Jamie

    Jamie Guest

    WHich is why you're not suppose to attach the wire to the studs of the
    wall, but lay them between. Most people hanging pictures and the like
    love to find the stud and drive a nail into it. if you're using the stud
    to attach the wire or straps for the conduit, this means they're in
    close proximity of the nail coming through and the person should miss
    the stud or go side ways into it.

    of course, open structures line barns and such normally do require pipe
    of some kind if its reachable, for protection of the occupant and you
    can then use the studs, beams etc..
    How ever, if that structure ever becomes a sight where walls are to be
    installed, then, The way I understand it, these stud/beam mounted
    electricals are to be moved so that any nailing into the stud via the
    wall will not hit a wire..

    Which is why most new houses have the romex hanging between the studs.
    Oh, who reads code any way, I'm sure towns/cities have their own
    additional codes they must go by, I know that is how it's down here..
     
  17. Jamie

    Jamie Guest

    Really,..
    I have a state inspector friend I should have log in here., What he
    tells me and shows me from the book and local codes, is totally
    different what what I've seen here, when it comes to house residential
    wiring and industrial installations.

    I think he'd like showing you some code books. He also does adult
    refresher courses and he tells me that it's hard to believe the number
    of those that have been in the business for years having a miss
    conception of what they think should be done..

    He used to be part of the NEC group committee but since he has retired
    from tech school teaching he has pulled out of that.


    Have fun with your many wonders..

    I'll get off this soap wagon now because I know where it's leading.

    Too many bone headed people here..

    I'll stick with the NEC and local codes for now.. Thank you very much..
     
  18. Josepi

    Josepi Guest

    I think you will find what he stated was correct. In Canada the code states
    more like 1.5" back from the wall surface. On a 2x4 wall that means in the
    centre. In the USA that means in the center.

    Cable must be fastened (not sure of exact wording in code) within 6" of any
    box. That gives strain relief to the wire connections and stops wire flop
    from getting caught in the drywall and picture nails.

    Yes, there are many bone headed people here, as in all Usenet groups. The
    flaw comes and goes with most people. Take each post for what it is worth to
    you.



    Really,..
    I have a state inspector friend I should have log in here., What he
    tells me and shows me from the book and local codes, is totally
    different what what I've seen here, when it comes to house residential
    wiring and industrial installations.

    I think he'd like showing you some code books. He also does adult
    refresher courses and he tells me that it's hard to believe the number
    of those that have been in the business for years having a miss
    conception of what they think should be done..

    He used to be part of the NEC group committee but since he has retired
    from tech school teaching he has pulled out of that.


    Have fun with your many wonders..

    I'll get off this soap wagon now because I know where it's leading.

    Too many bone headed people here..

    I'll stick with the NEC and local codes for now.. Thank you very much..
     
  19. Thomas

    Thomas Guest

    Not according to 2008 NEC (NFPA 70). I refer you to 334.17, Through or Parallel
    to Framing Members, which directs you to 300.4.

    300.4(A)(1): "In both exposed and concealed locations, where a cable- or
    raceway-type wiring method is installed through bored holes in joists, rafters,
    or wood members [studs in residential structures are typically wood, yes?],
    holes shall be bored so that the edge of the hole is not less than 32 mm (1-1/4
    in.) from the nearest edge of the wood member. Where this distance cannot be
    maintained,the cable or raceway shall be protected from penetration by screws or
    nails by a steel plate(s) or bushing(s), at least 1.6 mm (1/16 in.) thick, and
    of appropriate length and width installed to cover the area of the wiring."

    Exception 1 states that guard plates shall not be required to protect RMC, IMC,
    RNC [!!! [1]], or EMT.


    Correct. 300.4(D). Same requirements as for holes: 1-1/4 in. from edge or
    protected by 1/16 in. steel plate. Exception 1 allows the guard plate to be
    omitted for RMC, IMC, RNC [!!! again [1]], and EMT.

    334.30: No greater than 4-1/2 ft. and within 12 in. of every outlet box, J-box,
    cabinet, or fitting.
    Yep. Always practice safe wiring. And NEVER EVER EVER EVER EVER use *GREEN* wire
    nuts on *ANYTHING* but EGCs. Not even temporary wiring, no matter if it's 50 ft.
    off the floor or not. (I know a *licensed master electrician* who does, just
    because he ran out of yellows or reds and can't be bothered to go get more off
    the truck that's 15 ft. way.)

    Wrong. 300.4(D) and 334.30.

    Correct. 334.30(B)(1).
    I'm glad I don't live in your state. Scary, your state inspector in regards to
    wiring methods.
    Can't say about your local codes, but I *do* know what the 2008 NEC states,
    because I have it in my lap as I type this, and quoted from it as I did above.
     
  20. Thomas

    Thomas Guest

    Thomas wrote:

    WHOOPS! Left out my footnote:

    [1] RNC is soft in comparison to RMC, IMC, and EMT. I can, and have, driven a
    nail, with moderate effort, through RNC with a 16 oz. hammer. And RNC is going
    to protect wires or cable from a nail or screw???
     
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