|
In order to have an
inductive loop system operate as a reliable system, it is necessary to pay
careful attention to the loop installation. The use of proper installation
techniques can reduce unnecessary problems, while increasing reliability. The
following guidelines should be observed.
1. The saw slots must be the proper depth, clean, and with out any sharp corners
which could damage the wire insulation during installation.
2. If a splice is required between the loop and the control box, it is
recommended that a shielded, twisted pair of equal gauge be used from the splice
to the control box. The IMSA Spec No. 50-2-84 lead-in wire meets these
requirements. The shield must be floated (left unconnected and insulated) at the
splice end and shall be grounded to earth ground at the cabinet end only. Any
other grounding arrangement can lead to erratic system operation.
3. All splices must be soldered, even when initially done with crimp type
splices. Wire nuts are not allowed. Each splice point must be protected with a
moisture proof seal. Failure to observe these precautions is the most common
cause of future problems in the system.
CAUTION: When soldering, use
only enough localized heat to adequately flow the solder through the connection
without burning the surrounding insulation. Soldering should be done with a
copper tip iron. Do not use direct flame.
4. It is very important that the loop connections be accessible for maintenance
and repair.
5. The correct separation of loops on separate adjacent systems is important to
prevent crosstalk. The minimum distance is equal to the longest short side of
the loops in question or 3.0’ witch ever is greater. Example: One loop is 2.5’ X
6.0’, the other 6.0’ X 10.0’. The longest short side is 6.0’. This equals the
separation required.
6. When making the final connections in the control box, crimp type connectors
should be soldered for additional security and the screws on the terminal strip
securely tightened. Adding lock washers is a further deterrent to the screws
loosening due to vibration over time.
7. When two loops are used on the same detector, they should be connected in
series. The direction in which the current flows in each loop is important for
proper door operation. (See Loop Phasing)
8. Non-metallic conduit is required for housing the lead wires from the loop to
the control box. However, building codes call for metallic conduit to protect
wires that are installed on the out-side of walls or in areas where the wires
may risk damage. If a long run of metal conduit is required (over six feet), it
is recommended that a junction box be placed as close to the loop as possible
and IMSA Spec No. 50-2-84 lead-in wire be used from that point to the control
box. The metal conduit and shield from the lead wires must be securely grounded.
9. Choose a sealant carefully. It must be suitable for the application and the
pavement. LIS can supply sealant specifically designed to match the various
temperatures and surface materials encountered when installing loops.
10. For industrial applications, It is advisable to clearly mark the area where
the loop is installed. This will enable the drivers to avoid traveling over the
loop when they do not require the door to open. Marking may be accomplished with
a good grade epoxy paint or black dye mixed with the loop sealant before the
loop is sealed.
11. When installing a preformed Paveover loop, the same careful attention to
proper electrical installation techniques described above apply. The
Paveover style loop is recommended for new construction in concrete, asphalt or
gravel.
|
