5.
Loop and lead-in wire should be one continuous
piece. Avoid splices, if possible. If a splice is
necessary for any reason, “pot” the splice in
epoxy or use heat shrink to ensure that the
quality of the splice covering is the same as
the original wire jacket.
6.
Use only 14, 16, or 18 gauge stranded wire with
a direct burial jacket. Cross linked polyethylene
insulation types, such as, XLPE or XHHW, will
last much longer and are less prone to damage
during installation than conventional insulation
types. Preformed loops can be used before
road surfacing or under pavers.
7.
Twist loose tails of lead-in wires tightly,
approximately ten times per foot. See Figure
69.
8.
Follow this guide for the correct number of
turns in the loop; 12 to 20 sq. ft = 5 turns; 20
to 60 sq. ft. = 4 turns; 60 to 240 sq. ft. = 3 turns;
3.7 to 6.1sq. m = 5 turns; 6.1 to 18.3 sq. m = 4
turns; 18.3 to 73.1sq. m = 3 turns
Figure 69. Wire Twist Lead-ins
9.
This guide is written from a design perspective,
but installation workmanship practices are
equally important to insure proper operation
and long loop life. The best way to insure a
quality installation is to employ a professional
installer experienced with detector loops. A
few important practices are:
The slot in the surface of the road should be cut
¼-inch wide x 1½-inch deep (6.3mm x 38.1mm).
The corners of the cut must be at an angle or
core drilled to relieve stress on the wires.
Twist lead-in at least
10 turns per foot
Like This
Not Like This
h
his
Twist Like This
After the wire is installed, the slot must be
completely backfilled with a non-hardening
sealer. If the loop wires are able to move in the
slot after the sealer has set, the detector may
give false calls.
Figure 70. Loop Sealant
Detector Logic
HySecurity recommends that vehicle detectors
be used for free open and obstruction sensing
logic only. Because of their slower speeds, closing
logic is a poor choice for security gate systems.
Since there are several ways that the gate may
be left standing open and because there is a loss
of safety, our circuit has not been designed to
accommodate “detect to close” logic.
Loop Diagnostics
The following tests cannot guarantee a functioning
loop, but failure of either test means that the loop
is de
fi
nitely suspect, even though it may still be
functioning at the time.
1.
Test the resistance of the loop and lead-in wire.
It should not exceed 4 Ohms.
2.
Test the resistance between the loop and
earth ground with a 500V Megohm meter. It
should be 100 Megohms or more. Loops may
function at 100 Megohms or less but will not
be reliable (e.g. when the ground is wet from
rainfall). Low resistance indicates broken or
moisture saturated insulation. This is common
if inappropriate wire insulation has been used.
A schematic for a slide gate loop layout is shown
in Figure 71.
ACCESSORY CONNECTIONS
MX4505 Rev. E ©2020
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