When would you typically choose plenum-rated cable (CMP) over riser-rated (CMR)?

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Multiple Choice

When would you typically choose plenum-rated cable (CMP) over riser-rated (CMR)?

Plenum-rated cable is chosen for paths where conditioned air is moved through the building, such as above ceilings or under raised floors in air‑handling spaces. These plenums can quickly spread fire and smoke, so CMP jackets are tested to limit flame spread and smoke/toxic gas production, helping keep the air in the HVAC system safer during a fire. That’s why the correct scenario is where the cable would be in an air‑handling space and fire/smoke control is required. The other environments don’t place cables in spaces that the HVAC system uses to move air. Outdoor underground runs, wet locations, or short patch cords inside racks don’t require the stringent plenum ratings, so other, more appropriate cable ratings are used depending on moisture, exposure, and physical path.

Plenum-rated cable is chosen for paths where conditioned air is moved through the building, such as above ceilings or under raised floors in air‑handling spaces. These plenums can quickly spread fire and smoke, so CMP jackets are tested to limit flame spread and smoke/toxic gas production, helping keep the air in the HVAC system safer during a fire. That’s why the correct scenario is where the cable would be in an air‑handling space and fire/smoke control is required.

The other environments don’t place cables in spaces that the HVAC system uses to move air. Outdoor underground runs, wet locations, or short patch cords inside racks don’t require the stringent plenum ratings, so other, more appropriate cable ratings are used depending on moisture, exposure, and physical path.

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