Page 84 - Optical Communications Essentials

Optical Fiber Cables

74 Chapter Five

Figure 5.7. Example of an indoor distribution
cable. (a) Distribution cable cross section;
(b) loose-tube cross section (one or more fibers).

are designed for use in intrabuilding trays, conduits, backbone premise path-
ways, and dropped ceilings. A main feature is that they enable groupings of
fibers within the cable to be branched (distributed) to various locations.

5.3.2. Indoor cable applications
For indoor cables the National Electrical Code (NEC) in the United States
requires that the cables be marked correctly and installed properly in accor-
dance with their intended use. The NEC identifies three indoor cable types for
different building regions: plenum, riser, and general-purpose areas. Table 5.2
lists some common indoor cable applications and their markings. A basic dif-
ference in the cable types is the material used for the outer protective cable
jacket. NEC Article 770 addresses the flammability and smoke emission
requirements of indoor fiber optic cables. These requirements vary according to
the particular application, as described here:

■ Plenum cables. A plenum is the empty space between walls, under floors, or
above drop ceilings used for airflow; or it can form part of an air distribution
system used for heating or air conditioning. Plenum-rated cables are UL-
certified by the UL-910 plenum fire test method as having adequate fire resist-
ance and low smoke-producing characteristics for installations in these spaces
without the use of a conduit. As noted in Table 5.2, these cables are termed
OFNP (optical fiber nonconductive plenum) for all-dielectric cables or OFCP
(optical fiber conductive plenum) when they contain metallic components.

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