What does moisture ingress look like?
Fogged lenses, water standing in a can, and insulation resistance that drifts down test after test — the slow warning that comes before the earth fault.
Moisture ingress is water getting into places that must stay dry: the fixture, the base can, the transformer pit or handhole, the connectors and the cable ducts. It comes in through the lens and body seal, the cover and pavement joint, cable and duct entries and connector seals, and it can travel along a duct or trench from a wet point. Seals are never perfect, so a base is built to drain; if the drain is blocked, water stands around the transformer and connectors.
It is rarely sudden. Insulation resistance falls first, often well before any fault appears, then corrosion, fogged optics and damaged insulation follow, and finally an earth fault or an open joint that can reach the whole series circuit. A wet structure is isolated, locked out and proved dead before it is opened.
- Read the symptom. Fog or water inside a lens, standing water in a can or pit, falling insulation resistance, flicker or an earth-fault indication.
- Check the pattern. One location, or several along the same duct or drain line; trend the insulation readings against the baseline.
- Isolate. CCR off, locked out and tagged; prove the circuit dead.
- Find the path. Look for water marks, corroded terminals, hardened, cracked or displaced seals and gaskets, the cable and duct entries, the pavement joint and a blocked drain.
- Clear, dry and test. Remove the water, clear the drain, dry the structure and test insulation resistance before anything is closed or resealed.
- Fix the path, re-test and record. Replace the faulty seal or gasket with the correct part, re-test, and log the result against the circuit.
Falls, gasketed covers, sealed joints and sealed entries keep it out. See water ingress prevention.
A drain hole, sump and pipe laid to a fall lead the rest away. See base-can drainage.
Frequently Asked Questions
Q1What is moisture ingress in airfield lighting?
Water getting into places that must stay dry: the fixture, the base can, the transformer pit or handhole, the connectors and the cable ducts. It lowers insulation resistance and can cause corrosion, damaged insulation, fogged optics and, in time, earth faults on the series circuit.
Q2How does water get into a fixture, can or pit?
Through the lens and body seal, the cover and the pavement joint around the structure, cable and duct entries, and connector seals. It can also travel along a duct or trench from a wet or low point. Aged, hardened, cracked or displaced seals and gaskets are the usual weak points.
Q3Why does moisture ingress often show up as falling insulation resistance first?
Damp lowers the resistance of the insulation before it breaks down enough to cause a fault, so the reading drifts down from test to test, often well before an earth fault appears on the circuit. Trending each result against the baseline is how it is caught early.
Q4What does moisture do to a series circuit?
Water inside a structure can corrode terminals and contacts, damage insulation, fog the optics and shorten the life of the LED, lamp or driver. On a series circuit a leak to earth can then become an earth fault on the whole circuit, and a corroded joint can open it.
Q5Why does a sealed base can still need drainage?
Seals are never perfect, so some water is expected. The base is designed to drain through a drain hole, a free-draining bed or sump and a pipe laid to a fall. If the drain is blocked, most often by grout, silt or debris, water stands around the transformer and connectors.
Q6Is it safe to open a wet can or pit?
Only after the circuit is isolated, locked out and proved dead. Water and damaged insulation can put voltage where it should not be, so treat every lead as live until the site's procedure says otherwise. Follow the permit-to-work and the manufacturer's instructions.
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