Hbiss... why would you only use plenum?
Because we almost always do commercial work. Most of our cable is run above dropped ceilings which are used for environmental air. For the few residential jobs or those not requiring a plenum listed cable it doesn't pay to go out and purchase a couple of reels of riser listed cable and keep them on the truck also.
This is also the reason we use CAT3 whenever we can. Plenum listed CAT3 is not that much more than riser listed CAT3. Plenum listed CAT5e is nearly twice the price of riser listed CAT5e.
-Hal
