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Plenum Rated Cable
Last Updated: 01/31/2017
  • CAT5e 4 Pair UTP

    25 Pair CAT3
    Top: Plenum (CMP)
    Bottom: Riser (CMR)

  • Cat5e U/UTP

    Coaxial
    Top: Plenum (CL2P)
    Bottom: Non-Plenum (CL2)

  • Cat5e U/UTP

    Fiber Optic
    Top: Plenum (OFNP)
    Bottom: Riser (OFNR)

Description:

Plenum: a space used for air circulation in heating and air conditioning systems. Plenums include raised flooring systems, air handling ducts and the space above a drop ceiling (though some building designs eliminate this area as a plenum by sealing it off from the HVAC system).

Plenum Rated Cable: the chemical composition of a plenum rated cable ensures that in the event of a fire the cable will self-extinguish, not reignite and will produce less smoke than a non-plenum cable. Plenum rated cable is typically constructed with fluorinated ethylene propylene (FEP) and is very similar to polytetrafluoroethylene (PTFE) in its chemical inertness, dielectric characteristics, coefficient of friction, and high-heat resistance. FEP also features high stress-crack resistance.

Application:

The NEC (National Electrical Code) requires that all cabling installed in a plenum space and not residing in conduit have adequate fire-resistant and low smoke producing characteristics.

Plenum rated cable is the only cable allowed in these circumstances. The installer is responsible for ensuring that all requirements are met before installation.

Riser rated cable is used in vertical installations that are not in plenum spaces (i.e. rising between floors, in elevator shafts.)

Common Cables with Plenum Option:

CAT3 CAT5e CAT6 CAT6A
RG6 RG59 RG11 Fire Alarm
Speaker Access Control Fiber Optic

Popular Manufacturers:

Related Industry Terms/Acronyms:

Riser Rated Cable - the chemical composition of a riser rated cable ensures that in the event of a fire the cable will self-extinguish and prevent the flame from spreading up the cable when installed vertically. Riser rated cable may not be used in a plenum space.

PVC Cable - a cable with a thermoplastic polyvinyl chloride jacket. PVC cable may not be used in a plenum space. Note also that a PVC jacket does not necessarily mean that a cable is riser rated. Some cable manufacturers produce CM rated or general purpose cable that does not meet the riser requirements.

  • CMP (Communications Plenum) – designates a communication cable suitable for installation in a plenum

  • CL2P (Class 2 Plenum) – designates a low voltage cable (power-limited, signaling, remote control) suitable for in-wall installation in a plenum up to 150 volts

  • CL2R (Class 2 Riser) – designates a low voltage cable (power-limited, signaling, remote control) suitable for an in-wall riser installation up to 150 volts

  • CL3P (Class 3 Plenum) – designates a low voltage cable (power-limited, signaling, remote control) suitable for in-wall installation in a plenum up to 300 volts

  • CL3R (Class 3 Riser) – designates a low voltage cable (power-limited, signaling, remote control) suitable for an in-wall riser installation up to 300 volts

  • CMR (Communications Riser) - designates a communication cable suitable for a riser installation

  • CM (Communications Multi-purpose) - designates a communication cable suitable for in-wall installation and may not penetrate floors – single floor use only

  • FPLP (Fire Alarm Power Limited Plenum) – designates a fire alarm cable suitable for installation in a plenum

  • FPLR (Fire Alarm Power Limited Riser) – designates a fire alarm cable suitable for a riser installation

  • OFNP (Optical Fiber Nonconductive Plenum) – designates a fiber optic cable suitable for installation in a plenum

  • OFNR (Optical Fiber Nonconductive Riser) – designates a fiber optic cable suitable for a riser installation

Comparison Chart:

Plenum Riser
Suitable for air handling spaces Not suitable for air handling spaces
Low smoke Suitable for vertical installations (i.e. between floors)
Self-extinguishing Self-extinguishing
Will not reignite Flame will not spread vertically

Further References:

  • NFPA (National Fire Protection Association)
  • IEEE (Institute of Electrical and Electronics Engineers)
  • UL (Underwriters Laboratories)
  • ANSI (American National Standards Institute)
  • TIA (Telecommunications Industry Association)

FAQs:

Does a plenum (or riser) rating affect the performance of the cable?

The plenum (or riser) designation refers to the characteristics of the cable’s outer jacket; therefore, these ratings are independent of performance.



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