What type of inductive loop wire should I use for an automatic gate system?

For most automatic gate saw-cut loops, use copper inductive-loop wire with cross-linked polyethylene (XLPE) insulation, commonly 18 AWG and specifically rated for direct burial and the selected loop sealant. Use one continuous conductor with no splices in the sensing loop, then tightly twist the lead-in pair from the pavement exit to the vehicle detector.

Why XLPE Loop Wire Is Usually the Correct Choice

An inductive loop is not simply a length of low-voltage control wire. The wire becomes the sensing coil for the vehicle detector. Its insulation must remain electrically stable while buried in concrete, asphalt, or another roadway material exposed to moisture, vibration, heat, and pavement movement.

XLPE insulation is commonly specified because it resists moisture absorption and abrasion better than many general-purpose building-wire insulations. For a field-wound saw-cut loop, look for wire identified for inductive vehicle loops or direct-burial loop applications. A common configuration is 18 AWG copper, but the detector and loop manufacturer’s instructions control the final gauge, conductor construction, and insulation requirement.

Why Standard THHN, TFFN, or Similar Wire Can Cause Problems

General-purpose PVC-insulated wire may look suitable because it is inexpensive and readily available, but it should not be treated as a universal substitute for direct-burial XLPE loop wire. Moisture reaching the insulation can change the electrical characteristics of the loop and cause frequency drift, intermittent calls, detector lockup, or a loop that retunes differently after rain.

Some installation methods permit specific PVC-insulated conductors only when a compatible hot-applied sealant completely encapsulates the wire. That is a system-specific exception, not a general recommendation. Cold-pour sealants may leave small voids if the groove, backer material, and wire are not properly filled. XLPE loop wire rated for the application is the safer default for most saw-cut gate loops.

Use a Continuous Loop Conductor

The sensing portion of the loop should be one continuous length of wire with the specified number of turns. Do not place wire nuts, crimp connectors, or underground splices inside the loop groove. The detector operates through a small change in inductance, so a weak or moisture-contaminated connection can produce unstable readings even when a normal continuity test appears acceptable.

Where a separate lead-in cable is required, follow the detector manufacturer’s splice and grounding instructions. A permitted splice is normally soldered, moisture-sealed, and placed in a watertight, serviceable junction box rather than buried in the pavement. Shield termination also matters: some detector systems call for the shield to be grounded only at the detector end and isolated at the loop end.

Twist the Lead-In Pair

From the point where the loop wires leave the roadway, the outbound and return conductors must be tightly twisted together. Six twists per foot is common installation guidance, but the detector manual should be checked. Twisting cancels most of the lead-in’s detection field and reduces false calls caused by wire movement, adjacent electrical conductors, or metal passing near the conduit route.

When to Use a Preformed Direct-Burial Loop

For new concrete pours, new asphalt, pavers, gravel lanes, or other surfaces where a saw cut is not the preferred method, use a factory preformed loop specifically rated for direct burial. These assemblies normally combine multiple loop turns, a protective outer jacket, a sealed transition, and an integral lead-in.

Do not select a preformed loop by outside dimensions alone. Verify the number of turns, lead-in length, cable construction, detector tuning range, burial method, and compatibility with reinforcement steel. The loop must be secured so it cannot float, collapse, or shift while concrete or asphalt is placed.

Match the Wire to the Sealant and Pavement

The loop wire, groove width, groove depth, backer material, and sealant must function as one installation system. The wire should sit securely in the bottom of the cut without sharp corner bends. Angled corner cuts reduce the chance of pavement edges damaging the insulation. Sealant must completely cover the conductors without voids that allow water intrusion or wire movement.

Concrete, asphalt, and paver installations expand and move differently. A rigid sealant that performs acceptably in concrete may crack or separate in softer asphalt. Confirm that the sealant is approved for the pavement, climate, wire insulation, and application temperature.

Before You Choose Inductive Loop Wire

• Confirm whether the loop is for free exit, reverse, presence, shadow, or another control function.
• Check the vehicle detector’s acceptable inductance range and recommended loop turns.
• Verify the specified wire gauge, conductor type, XLPE rating, and direct-burial approval.
• Choose a saw-cut wire system or a factory preformed loop based on the roadway construction.
• Confirm the total lead-in distance and whether continuous twisted wire or shielded lead-in cable is required.
• Match the loop sealant to the wire insulation and pavement material.
• Keep loop wiring separated from high-voltage conductors and account for nearby loops, rebar, and moving gate metal.
• Verify detector voltage, connector or socket style, relay logic, frequency settings, and control-board input requirements.

Loop Detection and Gate Safety

A vehicle loop is normally used to provide an exit command, hold-open signal, reverse command, or vehicle-presence input. It should not be assumed to replace monitored photo eyes, edge sensors, or other entrapment-protection devices required by the operator manual and the site’s gate-safety design. Confirm each input’s intended logic before connecting the detector relay.

Related Technical Categories

• Inductive Loop Wire and Preformed Loops
• Vehicle Loop Detectors
• Gate Operator Safety Devices
• Vehicle Detection Accessories
• Gate Control Boards and Expansion Modules
• Loop Sealant and Installation Supplies

Before selecting replacement or new loop hardware, verify the gate operator model, detector model, loop function, wire gauge, insulation type, number of turns, lead-in length, detector voltage, frequency settings, connector type, and control-board generation.