Wilson 400 Plenum cable’s flexible conductor enables tight bend radius that works in any install. The Wilson 400’s UL tested fire resistant jacket also keeps your space safe from potential hazards. Plenum cable is mandated to be installed in any "air handling" space by the National Electric Code. Knowing when a space requires Plenum Cable is very important. One of the easiest ways to do this is to look into the ceiling. If you see a duct going back to the Air Hauler then this means you have a Closed Air System, however if there isn't a duct running back to the Air Hauler then you have an Open-Air System, and this is a Plenum Space and will require Plenum Cable.