Re: Short Plenum Run Question

["Theron" <scary_penguin@xxxxxxxxxxx>]

Frank Olson wrote:
> Theron wrote:
> > L. M. Rappaport wrote:
> >
> >>On 29 Nov 2005 01:06:59 -0800, robertlbass@xxxxxxxxxxx wrote (with
> >>possible editing):
> >>
> >>
> >>>>In addition to Robert's coments, building codes may allow you to run
> >>>
> >>>standard FT-4 as well (for communications and network)...
> >>>
> >>>NOT in a duct.  This is a duct -- not a plenum -- and US code does not
> >>>permit any cables within it except those necessary to operate the duct.
> >>>
> >>>
> >>>>In Vancouver (for instance) you don't need to run plenum
> >>>>rated wire in a plenum if the total length of the wire run
> >>>>(from panel to device) doesn't exceed 9 meters...
> >>>
> >>>Same here although the distance isn't the same, but that rule does not
> >>>apply to ducts.
> >>>
> >>>Regards,
> >>>Robert L Bass
> >>>www.BassBurglarAlarms.com
> >>
> >>While you're right about those cables not being allowed in a duct, I
> >>am still not so sure it's a duct and not a plenum.  I've read and
> >>re-read his post and it still isn't clear to me.   It doesn't sound
> >>like everything is enclosed in tin and the wires may be below the tin
> >>part.  That sounds like a plenum, not a duct.
> >>
> >>Theron - do the wires go through a channel enclosed on all sides by
> >>sheet metal or is the only sheet metal on the top?
> >>
> >>No flame, just trying to visualize what he has.
> >
> >
> > Sorry - this is much more complicated than I imagined, but I appreciate
> > the help.
> >
> > Here's what I have - I have an interior wall in my basement, running
> > North-South and framed by 2x4 lumber separated 16" on center.  Two
> > adjacent gaps in the framed wall serve as a cold air return for the
> > furnace, as follows.
> >
> > On the West side of the wall is a living area, and the furnace is on
> > the East side of the wall.  On the relevant area, the west side of the
> > wall is tin, the east side is drywall.
> >
> > On the east side, I have a 30" wide grate about 6" off the ground to
> > allow air into the wall.  On the west side, I have two 8" ducts that
> > run from the wall to the furnace's main cold air return to allow the
> > furnace to draw air from the basement, through the wall.   Those ducts
> > are about 3-4' from the ground.
> >
> > At about 3" off the baseplate, I have a set of holes drilled through
> > the 2x4s on center running four cat 5e cables (3 phone, 1 ethernet).
> > Therefore, the cables run for about 30" across the bottom of the gap in
> > the wall I am using to feed cold air into the furnace.
> >
> > Here's an ascii, which should come out right with a non-proportional
> > font:
> >
> >  Top View            Side View
> >
> >   D x D            F     F     F
> >   D x D            F  8  F  8  F
> >   G x T888         F     F     F
> >   G x T            F     F     F
> >   G x T888         F     F     F
> >   D x D            GGGGGGGGGGGGG
> >   D x D            GGGGGGGGGGGGG
> >                    FxxxxxFxxxxxF
> >                    FFFFFFFFFFFFF
> >
> > D = Drywall      x = cat 5e cable, non-plenum rated
> > T = Tin             8 = 8 inch duct to main cold air return
> > G = grate         F = Framing lumber
> >
>
>
> Looks to me like you've got a plenum and not a "duct".  Now if you were
> to ask your local AHJ, he would tell you what you've done is a very big
> "no-no".  In fact, in most instances (and jurisidictions), he may even
> make you remove it.  I don't believe you're allowed to run *any* wire,
> combustible piping, etc. inside a cold air return although I have seen a
> couple of instances where vacuum piping was passed (go figure).  If you
> absolutely *have* to have it there, see if you can enclose it in metal
> conduit or a short run of BX (yes, it may mean you're going to have at
> least one splice).  The better way would be to find another route for
> your wire but that may not always be possible at this late stage.

My current plan is just to install a firestop between the cables and
the plenum or duct or whatever it is.  Since the cables are actually
below the grate, I can toenail some 14 1/2" blocks across the gaps and
block the area with the cables from the area where I want cold air to
circulate.  (That's what I would have done if I had realized what I was
doing at the time).