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Thread: FMC wiring methods

  1. #1
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    FMC wiring methods

    Article 300.22 refers to wiring in ducts not used for air handling,fabricated ducts for environmental air and other spaces for environmental air(plenums).I am reading 300.22(B) where it says wiring Only wiring methods consisting of Type MI cable, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in ducts specifically fabricated to transport environmental air. Flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these fabricated ducts.

    Now my question is lets say if you have a ducted return then does this 300.22(B) apply cause the way i am reading this is applies to wiring methods inside the ducts not the wiring method in the space itself.Am i right on this?

  2. #2
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    Quote Originally Posted by shortcircuit1 View Post
    my question is lets say if you have a ducted return then does this 300.22(B) apply
    ? I would say yes it only applies to wiring within the standard fabricated sheetmetal or flex duct (supply or return). Or a studbay turned in to a return air vent common in older residential basements etc.

    An area not fabricated exclusively for air handling but used for return air (plenum) like under a raised floor or above older office drop ceilings would be under 300.22(C) the way I read it.
    If your working in a drop ceiling that has a ducted return then 300.22(C) probably does not apply.

  3. #3
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    Quote Originally Posted by tortuga View Post
    ? I would say yes it only applies to wiring within the standard fabricated sheetmetal or flex duct (supply or return). Or a studbay turned in to a return air vent common in older residential basements etc.

    An area not fabricated exclusively for air handling but used for return air (plenum) like under a raised floor or above older office drop ceilings would be under 300.22(C) the way I read it.
    If your working in a drop ceiling that has a ducted return then 300.22(C) probably does not apply.
    Stud bay turned into air return duct isn't fabricated exclusively for air handling and fits in with the things you mentioned in your second paragraph.
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