How is a taxiway lighting circuit arranged?
Behind every taxiway light is a constant-current series loop. Edge lights, centreline lights and stop bars each get their own circuit, every fixture connects through an isolating transformer, and the system is split into zones so a fault stays local.
At most aerodromes, airfield lights are not wired in parallel like a building (parallel systems are mostly found at smaller airfields). Each circuit is a single closed series loop of primary cable driven by a constant current regulator, so the same current flows through every fixture’s transformer whatever the cable length. How the taxiway is divided into circuits decides what can be switched, what a fault can take out, and how a stop bar can be kept apart from the lights beyond it.
1One loop, one regulator
A CCR in the lighting vault feeds a closed loop of primary cable. Each fixture is coupled by an isolating transformer, which keeps the loop closed if a lamp fails. Brightness is set by changing the loop current, typically up to 6.6 A at the highest step, not the voltage.
2Separate circuits by function
Edge lights, centreline lights and stop bars are normally on separate circuits. Centreline lights are switched in sections so a cleared route can be lit, and a stop bar and the centreline lights beyond it must not be lit together (Annex 14 calls for the centreline lights beyond a lit stop bar to be extinguished over at least 90 m; confirm in your edition), which is easiest to guarantee when they are on different circuits and interlocked in the control system.
3Zoning
A large taxiway system is divided into several circuits by area. A cable fault or maintenance outage then affects one zone, each loop stays within its regulator's rating, and only the lights a route needs have to be on. For low-visibility operations, adjacent lights can also be interleaved on alternate circuits so the loss of one circuit still leaves a usable line of lights.
| Element | Arrangement |
|---|---|
| Power source | Constant current regulator (CCR) in the vault, one per circuit |
| Circuit type | Series loop of primary cable; same current through every fixture |
| Typical maximum current | 6.6 A, with brightness steps set by lowering the current |
| Fixture connection | Isolating transformer at each light |
| Edge lights | Own circuit(s), on/off and dimmed independently |
| Centreline lights | Own circuit(s), split into sections for selective switching |
| Stop bars | Own circuit, interlocked with the centreline lights beyond them |
Frequently Asked Questions
Q1What is a taxiway lighting circuit?
A series circuit: a constant current regulator in the vault drives one loop of primary cable through isolating transformers, and each transformer feeds one light fixture.
Q2Why are edge, centreline and stop-bar lights on separate circuits?
Each is switched and dimmed on its own. Stop bars and the centreline lights beyond them are interlocked so they are not lit at the same time, and centreline lights are switched in sections to show a route, so they are normally kept off the edge-light circuit.
Q3What does the isolating transformer do?
It couples each fixture to the series loop. If a lamp fails, the transformer keeps the primary loop closed, so one lost light does not take down the circuit.
Q4Why divide a taxiway system into several circuits?
Smaller zones keep a cable fault or maintenance outage local, keep each circuit within the regulator's rating, and allow only the needed taxi route to be lit.
Q5What happens if the series loop is broken?
The current stops for every light on that circuit and the regulator shuts down on open-circuit protection. This is why a taxiway system is split into several circuits, so one cable fault puts out one zone and not the whole taxiway.
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