Installation Cables are designed for permanent installation in walls and ceilings. Not recommended for applications where the cables will receive a lot of handling. If the ends of long cable runs will be handled often, these cables should be terminated at a wall plate and general purpose cables should be used outside the wall.

Plenum Cables are required by fire code when installed inside an air plenum and are easier to pull through conduit because of their smaller diameter and lower coefficient of friction.

PVC Cables are less expensive than plenum cables and are recommended for general applications but are not permitted in air plenums unless contained inside conduit.

What is a Plenum?

According to the National Electric Code (NEC) a plenum is a "compartment or chamber to which one or more air ducts are connected and forms part of the air distribution system." The concern is that during a fire, if there is burning material in a plenum air space, smoke and fumes can travel through air ducts to the whole building. For this reason, there are codes to restrict the types of materials (such as wiring) that can be placed in the plenum.

If wiring were placed inside air ducts, it would obviously have to be plenum rated. However, in many situations, the space above a suspended ceiling is used as a ductless return for an air handling system. In this case, since this space is being used as an air return, the entire space above the ceiling must contain only plenum rated materials. To determine if the space above your suspended ceiling is an air plenum, look for return ducts because, if they are present, the ceiling is probably not an air plenum. Plenum ceilings use grilles that allow air to pass through to the space above the ceiling but there are no ducts attached to these grilles.

What is the Code?

According to the National Electric Code (NEC), in plenum air spaces you must use plenum rated cables. Plenum cable is only required when cable is installed in a plenum air space. Materials kept below the ceiling — including speaker wire, computer cables, telephone cords, etc. — do not need to be plenum rated according to the NEC.

Remember that even though the National Electric Code may allow non-plenum cable, the final decision is up to your local Fire Marshall. Most cities adopt the national codes as their own without revision, but some cities modify or expand them and require plenum-rated cable in all situations. Regardless of the code or its interpretation, your Fire Marshall makes the final decision. We recommend that you contact your Fire Marshall if you have questions.