Secondary Lead Assembly

The Secondary Lead Assembly (also known as a transformer lead, secondary whip, or fixture lead) is a factory‑assembled cable assembly that provides the electrical connection between the secondary side of an AGL isolating transformer and the light fixture, sign, or beacon. It is a complete, ready‑to‑install unit that includes the secondary cable with pre‑terminated connectors on both ends, eliminating the need for field termination and significantly reducing installation time and potential wiring errors.

Key characteristics of secondary lead assemblies include:

• Pre‑Terminated Connectors: Factory‑fitted waterproof connectors (often the L‑823 or secondary‑specific connector types) on both ends, ensuring a reliable, weatherproof connection with consistent quality.
• Flexible Cable Construction: The cable features finely stranded, annealed copper conductors with flexible insulation (PVC, EPR, or TPU), allowing easy routing through fixture bases, junction boxes, and conduit.
• Low‑Voltage Rating: Designed for the stepped‑down secondary voltage from the transformer (typically 2.5V to 48V AC), with insulation rated for 600V or 1kV.
• Colour‑Coded Conductors: The conductors are colour‑coded (e.g., black/white, red/black) to identify polarity and simplify connection to the transformer and fixture terminals.
• Variety of Lengths and Configurations: Available in standard lengths (e.g., 1m, 2m, 3m, 5m) and with various connector combinations (plug, receptacle, or bare ends) to suit different transformer and fixture types.

The assembly is manufactured to meet the rigorous quality and performance standards of airfield ground lighting, ensuring reliable operation in the harsh outdoor environment. It simplifies maintenance and replacement, as the entire lead can be quickly swapped out without re‑terminating cables in the field.

The secondary lead assembly exists to remove field termination — and the variability that comes with it — from the connection between a transformer and its fixture. A hand-terminated joint made in the field, often in a cramped pit or handhole, carries real risk of an inconsistent crimp or a seal that isn't quite watertight, and either failure mode can introduce a fault into a circuit that otherwise would have performed reliably for years.

By pre-terminating both ends at the factory to a consistent quality standard, the assembly turns a connection point that used to depend on field conditions and installer skill into a simple, reliable plug-and-play component. This also speeds up maintenance directly: when a lead does eventually need replacing, a technician swaps the whole assembly rather than re-terminating cable in the field, cutting both the time a fixture is out of service and the chance of introducing a new field-termination error.

The secondary lead assembly is used throughout the airfield for all transformer‑to‑fixture connections, including:

• Runway Lighting Fixtures: Connecting runway edge lights, centreline lights, threshold lights, end lights, and touchdown zone lights to their isolating transformers.
• Taxiway Lighting Fixtures: Connecting taxiway edge lights, centreline lights, stop bars, clearance bars, and guidance signs.
• Approach Lighting Systems: Connecting ALSF‑1, ALSF‑2, MALSR, and other approach lighting fixtures to their transformers.
• Obstruction Lighting: Connecting obstruction lights on structures to their power sources.
• Airport Beacons: Connecting rotating beacons and heliport beacons to their transformers.
• Signs and Markers: Connecting illuminated signs, guidance signs, and other visual aids to their power supplies.
• Retrofit and Replacement: Replacing damaged or aged secondary leads during maintenance or system upgrades.

The assembly is available for various fixture types, with conductor sizes typically ranging from 1.5mm² to 4mm² (16 AWG to 12 AWG). It is designed for use in temperatures ranging from -40°C to +85°C and is resistant to oils, fuels, and de‑icing chemicals.

The lead assembly runs from the isolating transformer's secondary terminals to the fixture's own lamp/LED connector, typically inside the same base can or a short length of adjacent duct, kept short since it operates on the low-voltage secondary side rather than the field's constant-current primary. Connections at both ends are made with waterproof, submersible connectors (commonly L-823 or similar) rather than taped joints, since the assembly frequently sits in a base can that can flood; enough slack is left at the fixture end to allow the fixture to be lifted clear of its base can for maintenance without disconnecting the lead. Routing keeps the secondary lead separate from the transformer's primary-side series-circuit cable within the same can, so a secondary-side fault is isolated from the primary loop.

The secondary lead assembly provides a pre‑manufactured, reliable, and waterproof connection between the isolating transformer and the light fixture. Its design and construction ensure efficient power delivery and long‑term reliability:

• Cable Conductor: High‑conductivity annealed copper with fine stranding (Class 5 or 6) provides excellent flexibility, allowing the lead to be routed through tight spaces and around bends without damage. The stranding also reduces fatigue from vibration and thermal cycling.
• Insulation: Flexible PVC, EPR, or TPU insulation provides electrical isolation and mechanical protection. The insulation is rated for the secondary voltage and is resistant to moisture, oils, and chemicals commonly found on airfields.
• Connectors: Factory‑terminated connectors (typically L‑823 or secondary‑specific types) are moulded or crimped onto the cable ends. These connectors are designed to mate with the transformer's secondary terminals and the fixture's input socket, providing a secure, waterproof connection with low contact resistance.
• Strain Relief: The assembly includes integrated strain relief at the connector junctions, preventing the conductors from pulling out of the connector under tension.
• Colour Coding: The conductors are colour‑coded (e.g., black and white, or red and black) to indicate polarity, ensuring correct connection to the transformer and fixture terminals.

In operation, the isolating transformer steps down the primary current to a lower voltage and feeds it through the secondary lead assembly to the light fixture. The lead assembly carries this low‑voltage power to the fixture's lamp or LED driver. The pre‑terminated connectors ensure a consistent, low‑resistance connection that minimises voltage drop and heating, critical for maintaining the performance of the AGL system.

The secondary lead assembly carries no control logic of its own, but it sits on the far side of the isolating transformer from the loop the CCR actually regulates — the primary side carries the fixed loop current the ALCMS commands, while the secondary lead simply delivers whatever current that transformer's turns ratio produces to the fixture. This is the point of the isolating transformer: an open circuit anywhere in the secondary lead (a broken conductor, a failed connector) still allows the transformer's primary winding to remain part of an unbroken loop, so it does not, by itself, interrupt current to any other fixture on the circuit. Electrically, though, an open secondary lead presents the same impedance-rise signature at that transformer's primary as a burnt-out lamp or a failed transformer would — the CCR sees a loop voltage rise and reports a loop fault, with no way from the ALCMS console to distinguish a bad secondary lead from a bad lamp or a bad transformer at that position. Isolating the actual cause is a field task: checking the secondary lead's continuity and connector condition at that specific fixture once the loop fault has narrowed the search to it.

The secondary lead assembly consists of a length of secondary AGL cable, sized for the fixture's low-voltage, higher-current secondary circuit, factory-terminated at both ends with moulded or crimped connectors — typically an L-823-style secondary plug at the transformer end and a fixture-specific connector or bare lead lugs at the light end. The cable insulation and jacket are rated for direct burial or wet-location use within the base can, and the moulded connector bodies are over-moulded or potted around the crimp joints to create a factory-sealed, watertight termination that eliminates the need for field splicing. Strain-relief boots at each connector body protect the cable-to-connector transition from flexing and pulling stress during installation and maintenance. Assemblies are supplied in standard pre-cut lengths to suit typical base-can-to-fixture and transformer-to-base-can distances, with connector keying that prevents incorrect mating to other circuit types.