Unitec American Parking Equipment - Manual (Page 26)

Document Number: GC1001 22
Document Title: Unitec APE Gate and Gate Controller for Multi-Lane Applications Installation Guide
2.2 Loop Installation Tips
Loop Wire: The loop wire should be 16 gauge stranded tinned copper wire with
cross-linked polyethylene (XLPE) insulation rated for 600V.
Caution:
Do not use general-purpose building wire, which was designed for conduit
applications. It often has a very thin sheathing of nylon, which protects it from moisture,
but it is easily damaged during wire installation in the saw cut.
Sealant: Use a commercial loop sealant designed for traffic loops. Paving sealers, tar
and other products may work for a short time, but weather thermal cycles and vehicle
pressure will cause problems over time.
Backer Rod: Merge loops, which are much larger than the gate reset loop, may need
backer rods. Use a backer rod to ensure that the wires are in place and do not
vibrate. Any vibration or wire movement can cause a false detection.
2.2.1 Loop Wire Installation
A properly installed loop coil will provide reliable detection for a very long time with no
attention or maintenance. To do that, the following things must be true:
• Take care not to damage the loop wire insulation. Scratches on the wire
insulation, sharp edges or small stones in the saw cut, and sharp tools
used during the installation can cause damage to the wire. It is very
important in preventing a false detection and detector lockups.
• Avoid splices in loop wires. The loop wire continuity (or serial resistance)
should be low and constant. The current in the loop wire is too low to
overcome the long-term oxidation that is inevitable with splicing.
• The loop wire must not move or vibrate in the pavement. Any vibration of
the loop wires or movement of steel rebar, if used underneath the loop,
will cause false detection. Inspect the pavement before loop installation. If
you see large cracks in the pavement and evidence of pavement
movement, there is a potential problem. Pavement movement after you
have installed the loop can damage the wire, or cause false detection. If
necessary, use a backer rod to make sure that the wire is held firm in the
saw cut.
• Keep AC power at least 12” away from the loop. The loop wire must not
be subjected to electrical noise. AC power running under the loop can
cause false detection. The loop detector detects the changes in electrical
currents as if they were cars.
2.3 Other Useful Information
The following things can reduce the loop detector sensitivity:
• Underground steel reinforcing – make the loop saw cut shallow in existing
concrete pavement with steel bar reinforcement (approx. 1 inch) or use
fiberglass mesh when installing new concrete pavement. If possible, the
loop should be at least 6 inches from any steel reinforcing bars.