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Chapter 4:
Understanding Network Cabling
Learning to make coaxial cables with BNC connectors is fairly easy, but you need
two special tools to make the job easy. First, you need a wire stripper that will cut the
various parts of the cable to the right length. Many good strippers can do this for you
automatically; check with your cable supplier to order one. You also need a crimper
that both can crimp the central BNC pin onto the central conductor of the cable and
crimp the metal sleeve that holds the entire connector onto the wire. Again, you can
buy special crimpers that can easily do both jobs. The best crimpers use a ratcheting
mechanism to make it easier to exert the proper amount of force for a solid, reliable
connection.
Plenum Versus Nonplenum Cable
In a building, the area between the ceiling of the rooms and the roof of the
building is called the plenum space. Most buildings use ducts (big, flexible hoses)
to provide conditioned air to the rooms in the building, and they use the open
plenum space for air returned from the rooms. Typically, the air returned from the
rooms is partially reused by the air conditioning units to save energy because it's
already cooled or heated as appropriate. Occasionally, a building uses ducts for
the return air, but the standard for office space is simply to use the plenum space.
Why is this discussion of office building air handling important in a chapter
about cables? Because to run network cable through the ceiling of a building that
uses the plenum for return air, you must either install the cable inside special
piping, called conduit piping (which is extremely expensive), or use plenum-grade
cable. The difference between nonplenum cable and plenum cable is that the
plastics used in plenum cable do not give off toxic fumes in case of a fire. Because
most office buildings reuse the air in the plenum space, the last thing you would
want to happen is to have the cables redistributing toxic fumes if a fire broke
out somewhere in the building's roof or plenum space. A fire in a very small
area could cause the fumes from the burning cable to be distributed to a very
large area of the building because of how these ventilation systems work--most
definitely a Bad Thing.
Make sure to check with your cabling contractor for details about the
municipality in which you are installing network cable, but virtually all local
codes in the United States require either conduit or plenum-grade cable for
buildings with plenum air returns. It's important for the cable installer to be able
to handle any required wall penetrations that cross one-hour, fire-rated corridors
or building fire zones. Those wall penetrations must be properly sealed to
maintain the building's fire ratings.
Summary :
Because to run network cable through the ceiling of a building that uses the plenum for return air, you must either install the cable inside special piping, called conduit piping (which is extremely expensive), or use plenum-grade cable. The difference between nonplenum cable and plenum cable is that the plastics used in plenum cable do not give off toxic fumes in case of a fire. Make sure to check with your cabling contractor for details about the municipality in which you are installing network cable, but virtually all local codes in the United States require either conduit or plenum-grade cable for buildings with plenum air returns.
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