What is a secondary lead?
The short cable that carries power from the isolation transformer up to the lamp. It is the last link in the electrical path, so it has to be flexible, sealed and strain-free.
Airfield lights on a series circuit are fed through an isolation transformer. The secondary lead is the short cable on that transformer’s secondary side, linking it to the light source.
1It carries the lamp current
The lead is a two-conductor flexible cable with tough insulation. It leaves the transformer through a sealed connector, runs up the base or stem, and ends at the lamp or LED module. It is much shorter than the secondary cable that serves a remote load.
2Slack protects it
The lead is routed with a slack loop below the frangible coupling. If an aircraft or vehicle strikes the light, the upper part breaks away and the slack stops the lead from tearing out of the transformer or pulling the connector apart.
3Keep it sound
Look for cuts, abrasion, heat damage, a cracked or unsealed connector, water and strain. Never pull the lead tight, and replace a damaged lead with the correct part, refitted and sealed as the manufacturer specifies. Work on the lead only with the series circuit isolated, locked out and proved dead, because an open secondary can show a hazardous voltage.
| Element | Detail |
|---|---|
| Secondary lead | Short two-conductor cable from transformer to light source |
| Position | Secondary side of the isolation transformer, inside the fixture assembly |
| Conductors | Two insulated, flexible conductors |
| Connection | Plug-and-socket connector at the transformer; terminal or socket at the lamp or LED |
| Slack | A loop below the frangible point so the lead is never in tension |
| Check | Cuts, heat damage, sealed connector, correct routing, no strain |
Frequently Asked Questions
Q1What is the secondary lead of an airfield light?
The short insulated two-conductor cable on the secondary side of the isolation transformer. It carries the low-voltage power from the transformer up through the fixture base or stem to the lamp or LED module.
Q2What is the difference between a secondary lead and a secondary cable?
The secondary cable is the longer run between a transformer and a remote load. The secondary lead is the short tail inside the fixture assembly, from the transformer connector to the light source. Lengths and construction differ between products.
Q3Why does the secondary lead have slack?
Slack lets the lead flex without strain and lets a frangible mounting break away in an impact without tearing the lead or damaging the transformer. Leave the slack the manufacturer specifies, and do not pull the lead tight.
Q4What happens if the secondary lead fails?
A broken or open lead acts like a failed lamp: the light goes out, but the isolation transformer keeps the series loop closed, so the other lights stay on. An open secondary also stresses the transformer, so replace a damaged lead promptly. A damaged or water-soaked lead can instead cause leakage, heating or an earth fault. After any lamp-out, inspect the lead and connector before fitting a new lamp.
Q5Can a damaged secondary lead be repaired in the field?
Only as the manufacturer allows. Normally the lead is replaced with the specified part, the connector is refitted and sealed, and the circuit is isolated and proved dead first. Afterwards the lead is checked for correct routing and slack, and the circuit insulation is tested before it goes back in service.
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