A plenum-rated space is one that is used for circulating air back to the HVAC system. As such, the materials installed within the plenum area must be properly rated to resist flame spread and limit toxic fumes from being recirculated through the HVAC system. Plenum-rated cables have a fire-retardant jacket that emits fewer toxic fumes as they melt—which allows them to be installed “free-air” within a plenum space. Riser-rated cables have less fire-retardant characteristics and are designed to be installed between floors using building riser rooms as the pathway. Riser-rated cables can be installed in an overhead ceiling space if it is not being used for returning air into the HVAC system (i.e. ducted air return).