ETL 1110-2-533
30 Sep 94
Figure B-16. Communication equipment with unre-
strained circuit boards
Figure B-17. Communication cable tray
typically not incorporated in older equipment. A rod
placed across the front of the card cage through holes
(9) Communication equipment should be pro-
drilled in the ends of the cage can serve as a retain-
vided with emergency power. Emergency batteries
ing bar to keep circuit packs from vibrating loose. A
and back-up engine generators are vulnerable to
potential difficulty with this method of protection is
earthquake damage and were discussed in para-
that in the course of normal operations, restraining
graph B-4a. They are often a critical element to
rods are removed and then not replaced.
ensure the functionality of communication equipment
after an earthquake. Newer communication equip-
(8) Cable trays for communications systems such
ment is computer based, and the quality of emergency
as telephone, radio, and microwave systems are typi-
power may be higher than what was adequate for
cally different from those used for power or control
older systems.
cables. In many cases the cable trays provide bracing
at the top of communication equipment frames so that
e.
Microwave communications system.
their structural integrity is important. A common
design detail of communication cable trays is the use
(1) A reliable means of communication to offsite
of friction clips to connect cable tray sections (Fig-
command organizations and nearby facilities is vital.
ure B-17). Thus, structurally, components do not
Dams usually have several means of communication
have positive connections, even though they may be
to nearby facilities and the command structure. The
used to brace equipment frames. A simple strap
most obvious, and the most flexible, is the public
bolted to adjacent trays would provide a positive
switch network telephone system. This has not been
connection. If the tray is not used as frame bracing,
included in this section because these systems typi-
the addition of positive connections may not be war-
cally have traffic congestion problems and do not
ranted as the decoupling of a cable tray section is
function well during an emergency response period.
unlikely to damage the cables. Cable trays using top
They are unreliable in postearthquake situations and
brace equipment should be adequately anchored to
should not be relied upon as the primary means of
walls.
communication. Also, the Corps has little or no
B-11
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