What is plenum cable and do I really need to spend the extra money for plenum rated cat5? Because plenum rated Ethernet cable is required by local fire code in most installations where the cable will be used in plenum spaces (spaces such as air ducts, elevator shafts or some raised ceilings) we strongly suggest you check with your local authorities. CAT5 plenum cable while not truly resistant to fire does not emit the same amount of toxic fumes when burning. We offer bulk cat5 plenum cable in a variety of common colors. We also carry bulk 1000 ft shielded cat5 plenum STP cable should you need protection from EMI as well.