How is the secondary cable routed?
A short, low-voltage run from the isolation transformer to the light. It is protected in a sleeve, kept apart from the primary loop, and joined by plug-in connectors with slack so the fixture can be removed.
The secondary cable is the last short link in the circuit. It runs from the isolation transformer’s secondary terminals to the lamp or LED load in the fixture, and it is electrically isolated from the primary series loop. Because it carries the lamp load at low voltage, it is kept as short as practical; the long run is the primary cable.
For an elevated light or a sign, it leaves the can through a short sleeve or conduit, rises through the base and frangible coupling and reaches the fitting. For an inset light it normally stays inside the base can and rises straight to the fixture. Plug-in connectors at each end and a slack loop let the fixture or transformer be removed without disturbing the loop. Keep it clear of the primary cable, record connector and cable details 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 secondary cable in an AGL circuit?
The secondary cable is the short, low-voltage cable that runs from the isolation transformer’s secondary terminals to the lamp or LED load in the fixture. It is electrically isolated from the primary series loop, which is the long run.
Q2Why is the secondary cable kept short?
It carries the lamp load at low voltage, so every extra metre adds voltage drop and wasted power. It is kept as short as practical, and the maximum length is set by the transformer and fixture data.
Q3How is the secondary cable routed to an elevated light or sign?
From the can beside the fixture it goes through a short sleeve or conduit to the base, then up through the frangible coupling to the fitting. Plug-in connectors at each end, and slack, let the fixture be removed without disturbing the loop.
Q4How is it routed to an inset light?
Directly up from the transformer in the base can to the fixture, usually staying inside the can, with a connector at each end and enough slack to lift the fixture out.
Q5Is it safe to work on the secondary side of a live circuit?
Treat the circuit as live until it has been isolated and made safe under site procedures. An energised series transformer with an open secondary can present a hazardous voltage, so never open or disconnect the secondary on a live loop, and clear any open secondary found in service, such as a failed lamp, promptly.
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.