How is a fault isolated in a series circuit?
Make the circuit safe, read the symptom at the CCR, then narrow the fault down section by section until one part remains.
Fault isolation finds a fault in a series circuit by narrowing it down in steps. The circuit is first made safe: ATC is told, and the CCR is switched off, isolated and locked off. The symptom at the CCR then suggests the fault type. All lights out with an open-circuit alarm points to an open circuit, tested with continuity checks. A trip or earth-fault alarm points to an earth fault, tested with insulation resistance checks. Some lights out with the CCR running normally points to a local fault at a fixture, connector or isolation transformer.
For the first two, the circuit is divided at accessible points and each section tested. The method is half-split: test about half the circuit, set the good half aside, and split the bad half again until one section or device remains. After repair, the section and the whole circuit are retested, the CCR is restored and status confirmed, and the results are recorded. Test methods, limits and isolation points come from the manufacturer, the standards and the airport’s safe-working rules.
Frequently Asked Questions
Q1What is fault isolation in an AGL series circuit?
It is the step-by-step method of narrowing a fault down from the whole circuit to one section, cable, connector or device. The circuit is split into parts, each part is tested, and the part that fails is investigated further.
Q2What must be done before any fault isolation starts?
ATC is told as the airport procedure requires, and the CCR is switched off, isolated and locked off under the permit or safe-working rules. A series circuit carries a high current, so only trained and authorised personnel work on it.
Q3How does the symptom at the CCR guide the search?
All lights out with an open-circuit alarm points to a break in the loop. A trip or earth-fault alarm points to low insulation to earth. Some lights out with the CCR running normally points to a local fault at a fixture, connector or isolation transformer.
Q4What does half-split mean?
The circuit is divided roughly in half and one half is tested. The good half is set aside and the bad half is divided again. Repeating this finds the faulty section in a few steps instead of testing every point.
Q5Why test by section instead of at every light?
A series circuit can be long, with many lights, connectors and transformers. Testing section by section removes large parts of the circuit from doubt quickly, so the work and the time the lights are out are both kept down.
Q6What happens after the fault is found?
It is repaired, then the section and whole circuit are tested again, the CCR is restored and run, and status is confirmed. The findings and test results are recorded, and ATC is told the circuit is back in service.
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