Insulation on cables is subject to burn during a fire. The burning cable could possibly spread the fire to other parts of the building, and the fumes from the burning cable could be toxic to the building in-habitants. Cables are classified as three types based on their application and toxicity.

General Purpose cable is used for general horizontal wiring from the control unit to devices on the same floor. FPL-type cable is used on Power Limited Fire Alarm circuits, and NPLF is used on Non-power Limited Fire Alarm circuits.
Riser cable is used for vertical runs between floors. The jacket of riser cable is less toxic than General Purpose, and is more resistant to fire spread. Riser cable may be used in general-purpose applications, but general purpose may not be used in riser applications. FPLR is used on Power Limited Fire Alarm circuits, and NPLFR is used on Nonpower Limited Fire Alarm circuits.

Plenum cable is used for cable runs in environmental air spaces (plenums). A plenum is a chamber or compartment to which one or more air ducts are connected to form part of an air distribution system.
The jacket of plenum cable is less toxic than riser, or more resistant to fire spread. Plenum cable may be used in general purpose and riser applications, but general purpose and riser cables may not be used in plenum applications.

FPLP is used in Power Limited Fire Alarm circuits, and NPLFP is used in Nonpower Limited Fire Alarm circuits.

During the 1980s, a fire occurred at the MGM Grand Hotel in Las Vegas. Toxic fumes from the burning cable (nonplenum rated) were carried to other parts of the building.
More than 80 people died as a result of breathing the toxic fumes from the nonplenum rated cable. This incident started the widespread emphasis of plenum-rated cable.

CABLE SUBSTITUTION

Certain multiconductor (CM) type and coaxial (MP) type cables may be substituted for FPL-type cables. The cable grade can be replaced by the same grade (general purpose, riser or plenum) of the substitute cable. The same substitution rules for different grades apply as apply for FPL-type substitutions.

It is acceptable to replace general-purpose cable with riser cable. It is acceptable to replace riser cable with plenum cable. It is acceptable to replace general-purpose cable with plenum cable.

It is not acceptable to replace plenum cable with general-purpose cable. It is not acceptable to replace riser cable with general-purpose cable. A distinct hierarchy exits, with plenum cable being at the top and general-purpose cable at the bottom. — Contributed by Charles Aulner and Bryan McLane from the NTC Brown Book “Fire Alarm Systems Design and Installation,” available at www.NationalTrainingCenter.net.