[TriLUG] OT: how do I know if ethernet cable is plenum rated?

[Heath Roberts]

On Mon, May 26, 2008 at 8:58 PM, Joseph Mack NA3T <jmack at wm7d.net> wrote:

> On Mon, 26 May 2008, Steve Holton wrote:
>
> > Look for CMP, CL2P, or CL3P, but you may not find those.
>
> googling for these strings and downloading a few catalogs,
> it seems that anything ending in P (plenum) or R (riser)
> will do (I haven't found the difference between these two
> yet).


"riser" cable is more fire-resistant than "plenum" cable. You can use plenum
cable in a riser, but not riser cable in a plenum.

When I last looked (maybe 10yrs ago) plenum grade meant
> suitable for a plenum (eg air conditioning ducts), whereas
> now plenum grade cable is required for elevated floors and
> false ceilings, anywhere that if there was a fire the cables
> are required not to release toxic fumes (it seems this is
> anything except PVC). I don't know why cables lying on a
> floor don't need to be plenum rated. Presumably by the time
> the fire gets to the floor you're dead or gone.
>

The "plenum" is a structural space where mechanical systems move air. So a
raised floor in a computer room is a "plenum" if you've got air handlers
pushing air into it. This isfairly common in computer rooms, but not all
raised floors are used as plenums. The space above a suspended ceiling is a
plenum if it's used to return air to the HVAC system, but it's not a plenum
if the return (as well as supply) air is contained in ductwork.

A riser is open vertical structural space between floors that can provide a
chimney for fire or smoke. Generally the walls of the riser are constructed
to be fire resistant.

The "cables lying on a floor" don't need to be plenum-rated if they're just
lying on a floor. It's when you put them into a space where there's forced
air moving around, like the space under a raised floor used to move cooling
air. The intent is that if a fire starts in the plenum space, the
plenum-rated cable will release a significantly smaller amount of smoke and
poisonous gas, which kills people before they actually burn, than non-plenum
rated cable.

-- 
Heath Roberts
htroberts at gmail.com