AGL Secondary Lead for Airfield Lighting

An AGL secondary lead is the flexible electrical connection between an airfield lighting isolating transformer and the associated light fixture. It carries power from the secondary side of the transformer to the individual fixture, so it must be selected according to the transformer interface, fixture requirements, connector arrangement, cable construction and installation environment. It is used where the transformer and fixture are installed separately, for example within a transformer pit or light base.

They are used with runway edge, threshold, end, centreline and touchdown zone lights, taxiway edge and centreline lights, stop bar and runway guard lights, approach lighting fixtures, and inset and elevated fixtures. They are also used for new installations, rehabilitation, fixture and isolating transformer replacement, maintenance and spare-parts requirements.

Select it as a complete connection system rather than by lead length alone. Identify the isolating transformer (manufacturer, model, rating, secondary interface and existing lead details), the light fixture (manufacturer, model, type, wattage and existing connector arrangement), the cable requirements, the required length, the connector requirements and the installation environment.

One end must match the secondary interface of the selected transformer, and the opposite end must be compatible with the fixture, which can depend on the fixture manufacturer, model, wattage, lead arrangement, connector configuration, termination method and physical connection dimensions. It must also be compatible with the selected connectors, including lead diameter, conductor size, insulation construction, termination and sealing system. For replacement projects, identify the existing fixture and connector before selecting the replacement lead.

The required length can depend on the transformer and fixture locations, light base configuration, transformer pit dimensions, cable routing, connector position and the required maintenance flexibility. It also depends on the added secondary load, because a long lead adds resistance and must stay within the transformer rating. The lead should be long enough to allow proper installation and maintenance without creating excessive loose cable.

The lead should provide suitable electrical insulation, an appropriate conductor construction, the required flexibility, mechanical durability, environmental resistance, and compatibility with the transformer, fixture and connectors. Conductor configuration, size, material, insulation, overall diameter and temperature rating should match the electrical requirements of the fixture and transformer, and flexibility should not come at the expense of required insulation or environmental performance.

They are model-specific, and the lead must suit the transformer secondary output and the fixture lamp current. Confirm the exact conductor, insulation, temperature rating, minimum bending radius and other values against the manufacturer’s documentation for the selected configuration.

Route it without excessive bending, maintain the specified minimum bending radius, and avoid sharp bends, excessive tension, pinching, abrasion, contact with sharp edges, unnecessary loops and mechanical interference with fixture components. In inset lights, consider limited space, fixture removal and moisture exposure. In a transformer pit, route it to allow transformer access, fixture connection, inspection, maintenance and drainage, without obstructing the pit cover. Allow freedom of movement for maintenance while keeping the lead controlled.

Provide the existing transformer and fixture nameplate details, the existing secondary lead, connector photographs, lead dimensions, existing cable markings and installation photographs. If the transformer or fixture has been replaced with a different model, review compatibility before reusing the existing lead.

Checks may include visual inspection, lead identification, connector inspection, mechanical security, insulation condition, continuity testing where applicable, insulation resistance testing where specified, fixture operation and series-circuit verification, following the approved project procedure. During maintenance, look for damaged insulation, cuts or abrasion, excessive bending, loose terminations, connector damage, moisture ingress, mechanical stress and heat damage.

A fixture that is not operating can come from a damaged secondary lead, an open conductor, a loose termination, a failed secondary connector, a transformer secondary fault, a fixture fault or a primary series-circuit fault. Intermittent operation can come from a loose connection, damaged conductor, cable movement, moisture ingress or mechanical stress. Repeated lead failure can come from an incorrect lead specification, excessive stress, incorrect routing, excessive bending, inadequate environmental protection or incorrect connector installation. Investigate it as a complete transformer-to-fixture connection.

No. An open series circuit driven by a constant-current regulator can produce dangerously high voltage, and an open secondary can still present hazardous voltage and damage the transformer. De-energise the circuit at the regulator, apply the site lock-out / tag-out procedure, verify the circuit is de-energised and the output isolated before touching conductors, connectors, splices or transformers, and work under the airport’s permit-to-work system. See the electrical safety warning on this page.