How are approach-light cables routed?
One trench carries the series cable out along the approach and back, with a short loop from it through each light’s transformer.
The approach centreline lights sit on the extended runway centreline, with crossbars across it, and all of them are fed by a series circuit. The primary cable therefore runs out along the approach and back to the regulator, with both conductors normally laid together in one trench beside the lights.
From that trench, a short loop of the series cable runs into the can at the base of each fixture and through the isolating transformer primary, so every transformer is in series with the circuit and not tapped across it, and a short secondary lead runs from that transformer to the lamp. Where the route passes under a road, taxiway or drain, the cable runs in a duct. The finished route is recorded on as-built drawings so faults can be found and later digging planned safely.
Frequently Asked Questions
Q1What is approach-light cable routing?
The planned path of the series cable that feeds the approach lights, from the vault or regulator along the approach area to every fixture and back.
Q2Why does the cable go out and return?
Approach lights are on a series circuit, so current must flow out through the lights and return to the regulator. The out and return conductors are usually laid together in the same trench.
Q3How does power reach each light?
Short loops of the series cable run from the main trench into the can at the base of each fixture and through the primary of its isolating transformer, in series. The transformer feeds that one lamp through a short secondary lead and keeps the series circuit unbroken.
Q4Why are ducts used at crossings?
Where the cable passes under a road, taxiway or drain, a duct protects it and lets it be replaced without digging up the surface.
Q5Why are as-built route records important?
They show where every cable lies. That speeds up fault finding and prevents accidental damage during later digging or construction.
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