What is cable testing?
A sequence of de-energised electrical tests on the primary cable, each answering a different question: is the loop complete, is the insulation sound, and where is the fault?
A series circuit’s primary cable carries the whole circuit’s current, so one weak length can put out every light on that circuit. Cable testing checks it in stages with the circuit isolated, locked out and proved dead: a visual check, continuity, insulation resistance, and, where specified, a high-voltage proof test. Before an insulation or proof test, the CCR and any transformers or equipment not rated for the test voltage are disconnected.
If a test fails, the loop is split at pits and connectors and each section is tested again to narrow down the faulty length, or a cable fault locator is used. Every result is recorded against the circuit so that the next test can be compared with it.
- Inspect. Visual and mechanical check of route, pits, joints and connectors.
- Continuity. Confirm the loop is one unbroken path.
- Insulation. Measure the insulation resistance of the conductor to earth.
- Proof. Where specified, apply a DC proof test to new or repaired cable.
- Locate. Split the loop at connectors or use a fault locator to find the fault (see cable fault location).
- Record. Log values and compare with the baseline and earlier tests.
Frequently Asked Questions
Q1What is cable testing in airfield lighting?
A set of electrical tests on the primary cable of a series circuit, carried out with the circuit isolated, to prove it is complete, properly insulated and able to take the stress of operation.
Q2Which tests make up a cable test?
Continuity, insulation resistance and, where specified, a DC high-voltage proof test, backed by a visual check beforehand and fault location when something fails.
Q3When is cable testing done?
On new installations before energising, at intervals as part of routine maintenance, and after a fault or repair to confirm the circuit is sound.
Q4How is a fault located on a series loop?
By splitting the loop at pits and connectors and testing each section, or with a cable fault locator. The section that fails contains the fault, and splitting it again narrows the position.
Q5Why are results recorded?
A single reading says little on its own. Comparing it with the commissioning baseline and earlier tests shows slow deterioration before it becomes a failure.
Q6Who may carry out high-voltage tests?
Only trained and authorised staff using calibrated instruments, at the voltage and duration the cable rating and specification allow, under the site permit-to-work procedure.
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