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Networking Fundamentals · Foundational

Plenum-Rated Cable (CMP)

Cable with a fire-resistant, low-smoke jacket required for installation in plenum spaces used for air circulation.

Definition

Plenum spaces, such as drop ceilings and raised floors that carry return air, require CMP-rated (or OFNP for fiber) cable under the National Electrical Code because burning PVC releases toxic smoke that would spread through the building. Plenum cable costs more than standard PVC cable.

Example

Cable run above a drop ceiling used as an air return must be plenum-rated.

Exam tip

Air-handling space = plenum cable; between floors = riser cable.

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