Planning the cable path
Page 34 OmniTrax Product Guide
Concrete (with metal reinforcement)
Cables can be installed in slots in metal reinforced concrete, provided the cable is installed above
the metal according to Sensor cable burial depths
on page 36. Sensor cable cannot be installed
too close to the metal reinforcement, or below the metal reinforcement, as there will be virtually no
detection sensitivity. As a general rule, do not install cables in concrete where the metal
reinforcement is less than 10 cm (4 in.) deep.
Asphalt
Asphalt has an extremely low conductivity, which must be taken into account when installing
sensor cables in asphalt. If the sensor cables pass through asphalt and native soil, the detection
field above the asphalt can be significantly stronger and wider than the detection field over the
surrounding soil.
For short length driveway or road crossings under asphalt where the sensor cable is buried in soil
on both sides of the asphalt surface, increase the burial depth beneath the asphalt to maintain
uniform sensitivity. One or two 7 m sections of conduit can be used to protect the sensor cables
where they pass beneath the asphalt surface (see Road and sidewalk crossings
on page 38).
Sensor cables that are installed in a large asphalt surface such as a runway or parking lot are
buried in trenches at the standard depth.
A stone dust bedding is recommended to protect the cables from being damaged by the larger
stones in the substrate. At least 7.5 cm (3 in.) of stone dust is required above and below the
sensor cables to protect the cables from the heat when the asphalt surface is restored. The stone
dust used as a protective bedding must be fine aggregate, which passes a 4.75 mm No. 4 sieve.
The remaining 15 cm (6 in.) to the surface level is comprised of compacted crushed stone, or
native soil, and repaved asphalt.
Crushed stone
Crushed stone as a topping or surface treatment is acceptable provided its depth is less than one-
half of the sensor cable burial depth (see Burial with a crushed stone topping
on page 102). Clear
crushed stone or natural rock larger than 1 cm (3/8 in.) can damage installed cables, especially in
locations where vehicles or heavy equipment pass over the buried cables. Coarse gravel can also
cause nuisance alarms during heavy rain, as rainwater drains rapidly through the rocks.
If site conditions require that sensor cables be buried in coarse gravel or crushed stone, use a
stone dust bedding in the trench to surround and protect the cables. At least 7.5 cm (3 in.) of stone
dust is required above and below the sensor cables to keep the coarse gravel away from the
cables. The stone dust used as a protective bedding must be fine aggregate, which passes a 4.75
mm No. 4 sieve. In addition, add a sand or stone dust topping over the surface of the gravel to help
fill the voids between the stones. This will further improve detection performance and help to
prevent nuisance alarms during rain.
Note Slot installation is no longer recommended for asphalt surfaces.
Note Always test the sensor cable installation for sensitivity and containment
BEFORE restoring the asphalt surface.
Note In some instances, ferrite beads may be required to prevent over-
sensitivity in asphalt. Contact Senstar Customer Service if you are
installing OmniTrax sensor cable in asphalt.
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