> The plenum type of cable has a "less toxic" smoke from its insulation Plenum cable uses Teflon insulation, so NO SMOKE IS PRODUCED WHEN BURNED. I've tested this myself with a propane torch (outdoors). The electrical Code may vary between commercial and residential installations, but plenum cable SHOULD be used in all plenums, including wiring trays, not just air-handling ducts. Suppose a cable get energized with 110/240 volts! People do the most unlikely things, so you should consider fire caused by short circuit, not just hot pipes. I think Chad got it right when he said it's not required if sealed behind sheet rock. PS If you don't have to use Teflon, you may not want to: the twisted pairs are "stuck" together making termination with RJ-48 (8-position connectors) difficult. You'll need to use a knife or razor blade to separate the pairs. If you're using punch-down style termination boxes, then there should be no issue.