AGL Cables, Connectors & Junction Infrastructure

AGL cables are the specialised power cables that carry the series current from the CCR to every isolating transformer and fixture. In FAA nomenclature they are designated L-824 underground electrical cable (AC 150/5345-7); the L-823 designation covers the connectors, not the cable itself. They are designed for underground, often submerged, installation with robust insulation (XLPE or EPR) and a metallic screen or armour for mechanical protection and earth continuity. Primary cables (typically 6 mm² or 10 mm² stranded copper) run between transformer pits; secondary cables (smaller gauge) connect the transformer to the fixture.

Connectors are the plug-and-socket or moulded joints that join cable sections to transformer leads and fixture leads — the L-823 family being the most widely used. They provide a watertight, low-resistance connection that must withstand thermal cycling and mechanical stress.

Junction infrastructure includes the handholes, pits, splice boxes, and cable glands that house and protect connections, facilitate maintenance access, and maintain the integrity of the buried cable network. Together, these elements form the complete power-distribution backbone of the airfield.

Because AGL circuits run as a series loop, this infrastructure's purpose is not just to deliver power to each fixture but to guarantee an unbroken, correctly insulated path through every cable, connector, and splice in the loop — a single failed joint or damaged cable can drop or unbalance the whole circuit rather than just the one fixture attached to it. That has to be achieved almost entirely out of sight and out of reach: buried, sometimes submerged, and rarely inspected directly, so the cables, connectors, and junction infrastructure are built to hold their insulation resistance, watertightness, and mechanical integrity for years of thermal cycling and ground movement without maintenance. Junction points (handholes, pits, splice boxes) exist specifically to give technicians a controlled way back into that otherwise-buried network when a fault does occur, so a single bad connection can be isolated and repaired without having to excavate the entire cable run.

This infrastructure is deployed across the entire airfield, from the CCR room to the furthest fixture:

• Primary Series Cable: Runs from the CCR to each isolating transformer in a daisy-chain or loop configuration. Typically buried at a depth of 0.5–1.0 m. As a single-conductor circuit it does not require phase colour-coding; cable is usually supplied black with a printed legend identifying type, size, and rating, and individual circuits/loops are distinguished on site by tags, marker tape, and as-built records rather than insulation colour.
• Secondary Cable: Connects the transformer secondary to the light fixture or sign, usually shorter runs within a fixture pit.
• Connectors (L-823): Used at every transformer primary and secondary connection, and for cable-to-cable splices. Supplied as mated plug-and-receptacle pairs per FAA AC 150/5345-26 in six styles — Style 3/10 (Type I, single-conductor, 5000 V) for primary leads, and Style 4/11 (Type II, two-conductor, 600 V) or Style 5/12 (Type II, single-conductor, 600 V) for secondary leads — rather than as tee or elbow fittings.
• Splice Kits: Used to join cable sections where a continuous run is not practical, or for repair after a cable cut.
• Handholes / Pits: Below-grade chambers that house transformers, connectors, and splices. They provide access for installation, testing, and maintenance.
• Cable Glands and Sealing Systems: Ensure watertight entry of cables into pits, connectors, and fixture housings.

The choice of cable type, connector style, and pit design is driven by the specific circuit (runway, taxiway, approach) and the environmental conditions (soil type, water table, frost depth).

Primary cable is direct-buried or ducted at a depth set by the applicable standard and local frost line, typically 0.5–1.0 m below finished grade, and routed to keep clear of the runway or taxiway's graded strip wherever the surface layout allows, with a marker tape laid above the cable to warn future excavation of its presence. Connectors are made up inside a handhole or transformer pit rather than in the open trench, so the completed joint sits in a chamber that can be reopened for testing or repair without disturbing the surrounding buried run, and each connector is potted, heat-shrunk, or otherwise sealed to the manufacturer's method before the pit is backfilled or closed. Handholes and pits are set flush with or just below finished grade, positioned clear of aircraft wheel paths and mower traffic, with a lid rated for the loads expected at that location, and their internal drainage or sealing is checked at installation so standing water cannot collect around the connections inside. Cable routing between pits is recorded on the as-built circuit drawing at the time of installation, since a buried series loop with unlabelled routing becomes very difficult to fault-find or safely excavate around later.

The cable network forms a continuous series loop that starts and ends at the CCR. Primary cables connect the CCR output to the first transformer, then daisy-chain from transformer to transformer, with the last transformer returning to the CCR to complete the loop. Each transformer's primary winding is connected in series with the cable, allowing the same current to pass through every unit.

Key functional aspects include:

• Current Carrying Capacity: Primary cables are sized for 6.6A or 20A continuous current with adequate margin for voltage drop over long distances (typically up to several kilometres).
• Insulation and Dielectric Strength: Cables are rated for the high voltages generated by the CCR (up to 5 kV) and must maintain integrity even when submerged.
• Mechanical Protection: Armouring or a metallic screen protects against accidental digging, rock abrasion, and rodent damage.
• Earth Continuity: A continuous earth conductor (often the cable screen) is bonded through connectors and pits to ensure fault current can return safely to the CCR.
• Connector Sealing: Moulded rubber boots and compression seals exclude moisture and maintain insulation resistance, which is critical for long-term reliability.
• Pit Drainage: Handholes are designed with drainage or sump pumps to prevent prolonged submersion, which accelerates connector and cable degradation.

Cables, connectors and junction pits carry no active electronics or control logic of their own — they are the passive medium the CCR's constant-current loop runs through, not a monitored subsystem in their own right. Their contribution to system architecture is structural continuity: primary cable carries the same series current from the CCR, through every transformer in the daisy chain, and back to the CCR to close the loop, while junction pits provide access points for splicing, testing and fault sectionalising without breaking that continuity. Because the cabling itself has no self-diagnostic capability, any degradation — a chafed conductor, a failed seal letting in moisture, a corroded connector — only becomes visible through its electrical effect on the loop: the CCR's voltage-versus-current monitoring detects the resulting impedance change and reports a loop fault, which is then localised to a specific pit or cable run through sectionalised testing rather than through any signal the cable generates.

AGL cables are constructed with a stranded or solid copper conductor at the core, sized to the circuit's current rating, surrounded by cross-linked polyethylene (XLPE) or ethylene propylene rubber (EPR) insulation chosen for its resistance to moisture, fuel, and de-icing fluid over decades of buried service, with a metallic screen or armour layer wrapped around the insulation for mechanical protection and to provide a continuous earth path along the cable run. Connectors joining cable to cable or cable to transformer follow the L-823 family standard, using tin- or silver-plated copper alloy contacts housed within a moulded rubber boot that compresses around the cable jacket to form a watertight, IP68-rated seal capable of withstanding continuous submersion in a flooded duct or pit. Junction boxes and cable pits housing these connections are built from reinforced concrete, polymer concrete, or heavy-duty polymer, with a load-rated lid bolted or clamped in place to withstand incidental vehicle or aircraft wheel loading while remaining removable for maintenance access. Cable routes between pits run through buried ducting or direct-burial trenches backfilled with selected material free of sharp aggregate that could damage the cable jacket over time.