How is the primary cable routed?
From the vault, through ducts and a trench along the pavement edge, under pavements in ducts, and through handholes and cans at the lights. The cable carries the series circuit’s regulated current out and back to the same CCR.
The primary cable is the long run of every series circuit. It leaves the airfield lighting vault through ducts, follows the edge of the pavement to each light, and returns to the CCR it started from. Along the pavement edge it is either direct-buried in a trench, on a bed of sand with warning tape above it, or pulled through ducts, to the depth and spacing the design and the standard call for.
Where the route has to cross a runway or taxiway, the cable goes through ducts beneath the pavement, with spare ducts, so it can be replaced without cutting the surface again. Handholes and manholes at junctions and changes of direction give access for pulling, splicing and testing, and each light’s can leaves slack for lifting a transformer out. A bare counterpoise conductor above the cable helps protect it against lightning surges. Record the route and every crossing on the as-built drawings, and treat the circuit as live until it has been isolated and made safe.
Frequently Asked Questions
Q1What is the primary cable in an AGL system?
The primary cable is the insulated cable that forms a series circuit loop. It carries the constant regulated current from the CCR out through the primary side of every isolation transformer and back to the CCR, so it is the long run of the circuit.
Q2How is the primary cable installed on the airfield?
It leaves the vault through ducts, then runs along the edge of the pavement either direct-buried in a trench or in a duct bank. It is laid in bedding, covered with warning tape and backfilled, to the depth and spacing in the design and the applicable standard.
Q3How does the cable cross a runway or taxiway?
In ducts installed beneath the pavement, normally with spare ducts, so a cable can be pulled in or replaced without cutting the pavement again.
Q4What are handholes and manholes for?
They give access at junctions, changes of direction and along long runs, so cable can be pulled, spliced, tested and traced. Cans and pits beside the lights play the same role at each light, with enough slack left to lift a transformer out.
Q5What is the counterpoise conductor?
A bare conductor laid in the trench above the cable to help protect it against lightning surges. It is bonded into the airfield earthing network as the design requires, but it does not make the cable safe to touch, so isolate and prove the circuit dead before any work.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.