Wallace Perimeter Security SPEEDGATE - Page 82

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INSTALLATION INSTRUCTIONS FOR OPTIONAL VEHICLE DETECTORS
Installaon of Vehicle Detecon Ground-Loop Systems
3.1.3 It is highly recommended that a connuous length of wire be used to form the loop and feeder
to the detector. Loop wire is typically 14, 16, 18, or 20 AWG with cross-linked polyethylene
insulaon which is very resistant to moisture absorpon and provides good abrasion resistance.
3.1.4 The wire used in the loop should have an insulaon rated for direct burial. Since moisture
can cause signicant changes in the dielectric constant of the wire insulaon, which results
in excessive loop (frequency) dri, choose a wire with an insulaon which is impervious to
moisture. Wires with Polyvinyl Chloride (PVC) insulaon (i.e., those labeled TFFN, THHN, and
THHN-THWN) should NOT be used since they tend to absorb moisture and crack easily.
3.1.5 Avoid potenal damage to the loop wire by inserng the wire in the boom of the saw slot
using a wooden sck or other blunt instrument. Ensure wires are pressed rmly into the slot.
Loose wires can cause false calls due to vibraon or sudden movement.
3.1.6 In most cases, the saw cut will end at the edge of the pavement or at a stub-out for a conduit.
Where the wires leave the saw cut they must be twisted together with a minimum of six (6)
twists per foot (30.5cm). See Figure 19.
Figure 19. Correct Loop Wire Twist Conguraon
NEVER use a screwdriver or a sharp
object for loop inseron, as this can
puncture loop wire.