[KwartzLab] plenum vs non-plenum

[Darcy Casselman]

Sweet! I like free... :D

On Wed, Sep 5, 2012 at 10:58 AM, Ben Brown <ben at kwartzlab.ca> wrote:
> I'll have a look, I may still have some plenum kicking around here you
> can have for free. I have cat5e as well, if you ever need some.
>
> Ben
>
> On 9/5/2012 10:49 AM, Darcy Casselman wrote:
>> Hm, that's not a bad idea.  There are a couple places I need to cross
>> over heading ducts, which gave the idea of fire-rated cable more
>> practical appeal.
>>
>> PrimeSpec looks like it only sells spools of 1000', which is way more
>> than I need.  And $185 is somewhat more than I want to pay.
>>
>> Darcy.
>>
>> On Wed, Sep 5, 2012 at 9:23 AM, Kevin Martin <kpmartin at thinkage.ca> wrote:
>>> Indeed the question is what is a plenum. The word (as far as building trades
>>> are concerned) originates in ventilation terminology, and applies to spaces
>>> such as that above a drop ceiling when it forms part of the ventilation
>>> system. In commercial buildings the space above the drop ceiling is often
>>> used as the air return to the HVAC unit. It also applies in residential work
>>> to the wall and floor cavities that form part of the cold air return on a
>>> forced air heating system.
>>>
>>> Wiring in such spaces which could generate plentiful smoke would be a safety
>>> concern because it could quickly get dispersed throughout the building.
>>>
>>> The Ontario Building Code defines: "Plenum means a chamber forming part of
>>> an air duct system."
>>> 9.34.1.5.  Wiring and Cables: (2)  "Where a concealed space in a floor or
>>> ceiling assembly is used as a plenum, electrical wiring and cables within
>>> the plenum shall conform to Sentence 3.6.4.3.(1)." Section 3.6.4.3 then goes
>>> into a long-winded description of the fire ratings of the materials that
>>> form the plenum itself as well as stuff like wiring that happens t run
>>> through a plenum.
>>>
>>> If the space above the drop ceiling is closed and not part of the HVAC
>>> system, it would not count as plenum space, any more that the sealed
>>> cavities within a wall between each pair of adjacent studs would.
>>> That being said I have never seen any special provision for regular power
>>> wiring when it passes through a wall cavity that happens to form part of the
>>> cold air return in a residential heating system, although it would seem to
>>> me that the same hazard would exist. This may just be a case of endemic lax
>>> application of regulations. Or perhaps this only occurs in walls, which are
>>> not covered by 9.34.1.5 (2).
>>>
>>> In any case if you only need a few short runs in true plenum space, you
>>> could enclose them in conduit (some of the provisions of 3.6.4.3(1) allow
>>> for this). This is essentially the solution used for power cables in plenum
>>> spaces, where one sees conduit and/or armoured ("BX") cable. This might be
>>> cheaper and/or simpler than buying all plenum cable or buying two types of
>>> cable and having to splice them.
>>>
>>> -Kevin Martin
>>>   the Papertrail Handmade Paper & Book Arts
>>>   New Dundee ON
>>>
>>>
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>>>
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