LOOP DETECTOR HANDBOOK
667/HE/20663/000 Issue 13 Page 7
2. INSTALLATION OF TRAFFIC LOOPS AND FEEDER CABLES IN SLOTS
Before the work is carried out, the tools listed in the General Principles
Installation handbook (see section 1.3.1) should be available.
2.1 Loop Cable and Slot Dimensions
Loop slots are cut into road surfaces for the installation of the following loop
cables:
998/4/70671/001 50/0.25 EPR insulated
998/4/85264/000 30/0.25 EPR insulated
998/4/82021/000 30/0.25 EPR/PCP insulated
The works specification specifies cable to be used.
Slots for the installation of cables must be of sufficient width to permit the free
entry of cables. Minimum slot widths are as listed:
998/4/85264/000 6 mm
998/4/82021/000 8.5 mm
998/4/70761/001 8.5 mm
Slot depths are dependent upon the number of turns in the loop or number of
conductors within a slot, as follows:
998/4/85264/000 4 mm x turns/conductors ) Plus 50 mm where
) slots are cut in a black
998/4/82021/000 6.5 mm x turns/conductors ) top cover, or 25 mm
) where slots are cut in
998/4/70671/001 6.5 mm x turns/conductors ) concrete.
Note: The number of turns is specified in Section 2.5.
2.2 Positioning of Loops and Loop Tails/Feeders
Loop locations containing the following obstructions should be dealt with as
indicated.
2.2.1 Metal Reinforcing
When installing loops in concrete roads containing a metallic reinforcing
mesh, there must be at least 50 mm of vertical spacing between the top of the
mesh and the bottom of the slot or loop cable. The same rule applies to metal
damp courses found in some elevated roadways.
2.2.2 Buried Metal Objects
Generally speaking, heavy metal objects such as girders and pipes have little
effect on System D and Turning Detector Loops, providing the nearest point is
50 mm or more below the loop.
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