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Use of any loop smaller than six feet square is not recommended where truck traffic will be present.
The size and number of turns in a loop may vary due to site conditions and magnetic materials in the area.
Refer to your systems layout for the location of the loop in relation to the gate.
1. Loops are normally wound into slots cut in the road surface. These slots vary in width depending on type of wires to be used and are backfilled with an appropriate loop sealant. For preformed loops in PVC, the slot must be a minimum of 1/2" wide. For XLP loops, the slot should be 1/4" wide. Confirm the size slot required for your loop wire before cutting slots. Note that the slots must be blown clean and dry before the loop wire is installed. Loops that are to be installed in reinforced concrete should be as high as possible above the reinforcing. If the distance between reinforcement and the loop is less than 3", significant loss of sensitivity may occur.
2. A loop slot must not contain any conductor other than the loop itself. Slots cut in the roadway for feeders normally contain conductors for one loop.
3. Total feeder length is normally limited to 1,000 feet.
4. Loops and feeders should be #14 or #16 XLP, or preformed in PVC. Standard insulated wire will not work in a loop application, as the insulation will not hold up over time.
5. Loops and feeders are normally made up from one continuous piece of wire, with the feeder twisted together with at least six twists per foot, starting at the end of the wraps for the loop and continuing all the way to the detector connection.
6. After installation of a loop, it is wise to check the resistance to earth with a 500V "megger". A resistance of less than 10 megohms is usually indicative of broken insulation, which can cause the detector to appear to go "off tune" from time to time.