2.4.2
Exterior
Enclosures to house wireline DTS equipment in an outdoor environment shall
meet the requirements of NEMA 250, Type 4.
2.4.3
Corrosion Resistant
Enclosures to house wireline DTS equipment in a corrosive environment shall
meet the requirements of NEMA 250, Type 4X.
2.4.4
Hazardous Environment
Enclosures in a hazardous environment shall meet the requirements as
specified in paragraph ENVIRONMENTAL REQUIREMENTS.
2.5
MESSENGER CABLE
A messenger cable system to support all aerial cable shall be furnished and
installed. The messenger system shall include all guys, hardware and
appurtenances needed to install the messenger cable. The messenger system
shall be capable of supporting the weight of the DTS cable with the
required messenger cable tensioning without exceeding 30 percent of its
rated breaking strength under 16 degrees C 60 degrees F conditions of no
ice and no wind. The messenger shall be sized so that ice and wind loading
normally encountered at the site does not cause the messenger to exceed 50
percent of its rated breaking strength. All appurtenances, guys, and
hardware shall be sized to exceed the required strength of the messenger
cable. Messenger cables shall be galvanized zinc coated steel or aluminum
clad steel.
2.6
TAMPER PROVISIONS
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NOTE: Use this paragraph when using this section
with Small Intrusion Detection Systems.
**************************************************************************
Enclosures, cabinets, housings, boxes, raceways, conduits, and fittings of
every description having hinged doors or removable covers, and which
contain any part of the DTS circuit, connection, splices, or power
supplies, shall be provided with cover operated, corrosion-resistant tamper
switches, arranged to initiate an alarm signal when the door or cover is
moved. Tamper switches shall be mechanically mounted to maximize the
defeat time when enclosure covers are opened or removed. The enclosure and
the tamper switch shall function together to disallow direct line of sight
to any internal components and tampering with the switch or the circuits
before the switch activates. Tamper switches shall be inaccessible until
the switch is activated; have mounting hardware concealed so that the
location of the switch cannot be observed from the exterior of the
enclosure; be connected to circuits which are under electrical supervision
at all times, irrespective of the protection mode in which the circuit is
operating; shall be spring loaded and held in the closed position by the
door cover; and shall be wired so that they break the circuit when the door
or cover is disturbed. Tamper switches on the doors which must be opened
to make routine maintenance adjustments to the system and to service the
power supplies shall be push/pull-set, automatic reset type.
SECTION 16792A
Page 13
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