Re: Short Plenum Run Question

[Frank Olson <Use_the_email_links@xxxxxxxxxxxxxxxxxxxxxx>]

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.