\rHI Dan:
CL3 is the rating of the outer jacket. It means it is is fire retardant and can be used in side the wall when connecting In-wall or In-ceiling speakers. So when you run the wire in the walls through the different stud bays and there is a fire the jacket will not burn and spread the fire inside the wall. It will just melt. It will also not give out any toxic fumes either when it melts. The FT4 rating is the Canadian equivalent. The CL3/FT4 rating is good for all residential and most commercial applications as well. It can not be used inside an heat or cooling duct in a commercial building. For that you would need a plenum or FT6 rated jacket. If you were using non CL3 rated jacketed cable on your home and had a inspector look at it he would make you remove it from the wall.
TL/4070\r