9. What type of wire should
be used for the loop?
Number 16 or 20 AWG stranded wire can be used. The
wire gauge is not critical to proper operation of
the loop detector. The wire should maintain its integrity
under the pavement stress. Since asphalt is more
flexible than concrete, it is recommended that a
heavier gauge wire be used for loop installations
The main consideration in selecting a wire for loop
installations is the type of insulation. Cross-linked
polyethylene (XLPE) insulation rated at 600 volts
is highly recommended over PVC insulation. Under
similar conditions, XLPE insulation will absorb approximately
one percent of the moisture absorbed by PVC. When
insulation absorbs moisture, loop drift occurs, which
if great enough, can cause false detections. XLPE
also has higher resistance to abrasion, heat, oils,
After insulation, and any time there appears to
be a loop related problem, the loop should be tested.
Use a MegOhm Meter to test the integrity of the loop
/ lead-in wire insulation. Readings of 100MO or less
indicate possible insulation damage. Use a Multimeter
to check the total resistance of the loop / lead-in
combination. Total loop / lead-in resistance should
never exceed 4 Ohms.
10. How far from a gate should the loop be
As the length of the sides of the loop that parallel
the gate increases, the inductance change caused
by the gate also increases. The graph shows the inductance
change for different distances between the gate and
the loop for different sized loops.
The closer the loop is to a gate, the more influence
the gate has on the loop! Hence, the detector sensitivity
must be set lower to ensure the gate will not cause
the detector to generate an output when the gate
The following rule should be observed: The longer
the loop, the greater the spacing must be between
the gate & the loop!
The inductance change at two feet is one third of
the change at one foot. At four feet, the effects
of the gate on the loop are minimal.