Ouch ouch.
Plenum rated wire isn't essentially fireproof (why can I see guys using a fireplace chimney as a conduit? "Ravi said it was fireproof"). It burns at a higher temperature - how much higher depends on the exact makeup and cable type (for instance, 8ga AC mains will burn at a higher temp than CAT5) and produces less smoke, and the smoke it does produce is less acrid. (Burn a chunk of pine in a bucket and give the smoke a good huff... now do the same with a vinyl garden hose - which one feels like you just inhaled a lungful of pins and needles?)
I just got my refresher course in CMP (communications plenum rated) wiring recently from the contractors pulling cable in the new arena - what else can you talk about when you're giving them a hand on a ladder yanking miles of cable all day?
In your case, that should be fine for under either a hot water or steam radiator. Just wanted to clarify how burn resistant CMP is before someone set their house on fire.
Bren R.
