Firewalls
As shown in Figure
, firewalls are
usually easily identified, they are usually concrete, cinderblock, or brick
structures that extend the full width of a room or passageway, from floor to
ceiling. There are no breaks in firewalls. Firewalls are designed to contain a
fire to a specific area by acting as a barrier. If it is necessary to go
through a firewall, there are procedures for penetrating the wall. These
procedures must be compliant with the National Electrical Code (NEC). A copy of
the NEC can be obtained from local electrical suppliers.
For this reason, it is important to make a note in the survey report of any
area where a design will have to penetrate a firewall. Another reason to make a
note of firewalls is that they will affect the RF signal. Many facilities have
firewalls with doorways. The doors are specially constructed and sealed to
withstand a fire for a specified burn-through time. Other than their heavy
construction, these doors are not easily identified. The doors can even appear
to be made of wood. If a set of doors is believed to be part of a firewall,
check to make sure. If the doors are part of a firewall, survey with the doors
closed. Closing the doors will have an effect on the coverage. Do not assume
that doors will always be open just because they are open during the survey.
Risers
Risers are often referred to as wiring closets. Risers
are the areas of the building where cabling, conduits, and plumbing may be run
from floor to floor. Risers are often stacked on top of one another, making it
easy to run cables to the height of the building. All four walls of a riser, as
well as the floor and the ceiling, act as firewalls. It is important to notate
the location of the risers. As with firewalls, risers require penetrations that
meet NEC standards and will require plenum-rated equipment.
Cable
Paths
Always design and measure cable runs in straight paths. If a
cable running north and south needs to be run in a different direction, always
make a 90-degree turn. Do not run the cable at an angle. Never measure the
distance from the point of network connectivity to the AP with a straight line.
If the distance is measured incorrectly and the customer gives the report to a
local contractor for an estimate, the estimate could be wrong. Also, the cable
run may be longer than anticipated and require a different type of cabling.
Service Loops
Calculate for a service loop on either end of
the cable run. Service loops are usually 3 m (10 ft) long. This loop gives the
contractor some extra cable in case it must be terminated numerous times.
Extra Cable
Adding an extra 15 percent of cable is usually enough
to ensure that there will be enough cable to run around unforeseen objects.
Notate the estimated extra cable percentage in the report. Otherwise, the
contractor may determine how much cable to add and decide that the run will be
out of specification.