Plenum Coaxial Cables

Plenum coaxial cable is used to transmit video, radio frequency and other electronic signals through plenum spaces in commercial, institutional and industrial buildings. These spaces may include air-handling areas above suspended ceilings or beneath raised floors.

Because air can circulate through a plenum and spread smoke throughout a building, cable installed there must meet stricter flame and smoke requirements than standard general-purpose coaxial cable. Common applications include video distribution, security cameras, broadband systems, antennas, broadcast equipment and building communication systems.

A plenum-rated coaxial cable uses insulation and jacket materials designed to limit flame spread and smoke generation during a fire. It must carry an appropriate plenum rating, such as CMP, for the installation and jurisdiction.

A standard PVC-jacketed coaxial cable should not be assumed suitable for a plenum space simply because its electrical specifications match the equipment. The cable must satisfy both the signal requirements of the system and the applicable building and electrical codes. Final approval may depend on the authority having jurisdiction for the project.

Yes. Plenum-rated coaxial cable can generally be installed in many locations where a lower-rated indoor communications cable would otherwise be permitted. This can simplify cable purchasing when one construction will pass through several areas of a building.

However, a plenum rating does not automatically make a cable suitable for outdoor exposure, direct burial, wet locations or industrial environments. Those conditions may require additional ratings for sunlight resistance, moisture, temperature, chemicals or physical protection. The full installation environment should always be reviewed before selecting the cable.

The cable’s nominal impedance should match the equipment, connectors and termination components in the signal path. Common coaxial impedance values include 50 ohms for many radio frequency and data applications and 75 ohms for video, television and broadband systems.

Using the wrong impedance can cause signal reflections, increased loss, distortion and inconsistent equipment performance. Impedance should be confirmed from the system documentation rather than selected solely by the cable’s size or RG designation. Attenuation, capacitance and operating frequency should also be considered for long runs or higher-frequency applications.

Provide the required impedance, conductor size, shielding construction, operating frequency, voltage rating, temperature range and estimated cable length. It is also helpful to identify the equipment being connected, the desired connector type and any maximum outside-diameter or flexibility requirements.

The request should clearly state that the cable will be installed in a plenum space and identify any required ratings or project specifications. Details about indoor or outdoor exposure, installation near electrical equipment and applicable building standards can help prevent the selection of a cable that performs correctly but does not meet the installation requirements.