What is the secondary cable?
The short lead on the lamp side of an isolation transformer — it runs from the transformer secondary to one lamp, and is separate from the primary cable that carries the series loop.
The secondary cable is the short lead on the lamp side of an isolation transformer. It connects the transformer secondary to the lamp or fixture and carries lamp current for that one fixture only. The series loop stays on the primary side, so the two cables do very different jobs.
It is typically a short two-conductor cable, rated for the much lower secondary voltage and terminated with secondary connectors, with slack left in the can so the fixture or transformer can be lifted out. Do not confuse it with the primary cable, the long series loop. A damaged secondary usually puts one lamp out and leaves the loop closed, but an open secondary on an energised transformer can develop a high voltage, so treat the circuit as live until it has been isolated, locked out and proved dead.
- Select. Choose the cable and connectors to suit the lamp load and the fixture.
- Route. Run the shortest practical lead from transformer to fixture, with slack in the can.
- Connect. Make up the secondary connectors at the transformer and the fixture, sealed against moisture.
- Test. Check continuity and insulation resistance of the lamp-side circuit.
- Record. Log the readings against the commissioning baseline.
Frequently Asked Questions
Q1What is the secondary cable in an AGL system?
The secondary cable is the short lead from the secondary side of an isolation transformer to the lamp or fixture it feeds. It carries lamp current for that one fixture only, not the current of the whole series loop.
Q2How is the secondary cable different from the primary cable?
The primary cable is the long series loop from the CCR that passes through every transformer primary. The secondary cable is a short, separate lead on the lamp side of one transformer, so a fault on it affects one fixture, not the circuit.
Q3What is the secondary cable made of?
Usually a short two-conductor cable with insulated stranded copper conductors under a common outer jacket, rated for the much lower secondary voltage (600 V class is common) and terminated with a secondary connector or plug at each end.
Q4Why is the secondary cable kept short?
It only has to span the distance from the transformer to the fixture. Keeping it short limits voltage drop and power loss on the lamp side and the chance of damage, and the slack left in the can allows the fixture or transformer to be lifted out for maintenance.
Q5What happens if the secondary cable is damaged?
Typically that one lamp goes out while the primary loop stays closed and the other lights keep working. An open secondary on an energised transformer can still develop a high voltage, so the circuit must be isolated, locked out and proved dead before anyone touches it.
Q6How is the secondary cable checked?
With the circuit isolated, by inspecting the cable, connectors and seals for damage or moisture, then testing continuity and insulation resistance of the lamp-side circuit and comparing the readings with the commissioning baseline.
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