Information Technology Reference
In-Depth Information
available in surface-mount versions that are easy to place above the ceiling grid on
the walls surrounding the open-office space.
The availability of small form factor (SFF) connectors for fiber makes this
method even more practical. The SFF connectors place two fiber strands in an RJ-
size modular jack that snaps into the outlet box in the same way as the modular
jacks designed for copper.
Because fiber is terminated and interconnected in a fundamentally different
manner from copper, all open-office wiring systems for fiber are considered to be
the MUTOA method. This is true whether you are using the standard horizontal run
from a telecommunications closet, or the optional centralized cabling method cov-
ered in Chapter 12.
Fiber cable strands are generally terminated in a male connector, which is inter-
connected by aligning the fibers in an adapter receptacle. The terminations and con-
nections at the hub/switch in the TR, at the patch panel, at the MUTOA, and at the
work area outlet are identical. The insertion and return loss that result from each
termination are comparable to a normal termination, and the only parameters that
must be watched are the total path loss and the optical bandwidth. As a result, the
point of interconnection of fiber runs can be just as easily placed in the open-office
area as in the telecommunications closet.
One of the side issues that arise in open-office cabling is the separation of commu-
nications cables from power cables. The reason for this is that there is some concern
regarding the potential interference from power cables, and there are naturally
safety concerns about having dangerous voltages in close proximity to low-voltage
communications wiring.
In other sections of this topic, we have discussed the issue of separation from
power cables. Many authorities have attempted to create guidelines on this issue.
The recommendations range from a 2-in separation in electrical codes all the way
to a 3-ft guideline from a building standards organization. This leaves a lot to the
imagination. What issues should be considered?
The interference issue is fairly straightforward. Electrical power lines are not
limited to carrying only 50 or 60 Hz electrical energy. They can, in fact, inadver-
tently carry interfering signals at hundreds of megahertz. In one famous case, a 243
MHz interfering signal, generated incredibly by a malfunctioning air-conditioning
relay, was carried hundreds of feet along power lines from the offending source.
Commercial and military aircraft use 243.0 MHz as an emergency beacon and com-
munications frequency; thus, this unusual power-line interference was very serious.
