How do you troubleshoot an intermittent fault?
A fault that comes and goes cannot be measured while it is absent, so the work is to record when it appears, repeat the tests and trace it to the joint, connector or cable that only misbehaves in some conditions.
An intermittent fault comes and goes: a flickering light, an alarm that clears, or a reading that wanders. It is hard to find because it often comes from a loose or wet connector, a damaged cable or a failing joint that only misbehaves in some conditions. Corrosion raises contact resistance, which can cause heating, intermittent faults or arcing in a series circuit. Because the circuit may be normal when an engineer arrives, the record is the main tool: the CCR code and readings are noted before any reset, and the event log and alarm history show when and how often the fault appears.
Each event is logged with its time, weather and brightness step so a pattern can show. Tests are made de-energised, with ATC told and the circuit isolated, locked out and proved dead, and a primary connector is never separated on a live loop. A continuity reading that will not settle points to an intermittent joint or a poor test connection, so the test lead is checked and the test repeated. Insulation resistance is taken under recorded conditions and trended against the baseline, because a value that keeps falling points to moisture, damage or ageing. Suspected sections are inspected, repaired and retested, and the result is recorded.
Frequently Asked Questions
Q1Why are intermittent faults hard to find?
They come and go. They often come from a loose or wet connector, a damaged cable or a failing joint that only misbehaves in some conditions, so the circuit can test normal when the engineer arrives.
Q2What are the usual causes of an intermittent fault?
Loose or wet connections, corroded contacts, failing joints or terminations and damaged cable. Corrosion raises contact resistance, which can cause heating, intermittent faults or arcing in a series circuit.
Q3Why record the CCR code and conditions before resetting?
A reset clears the evidence. The code, readings, time, weather and brightness step show when and under what conditions the fault appears, and the CCR event log and alarm history keep the pattern so repeat events can be compared.
Q4What does a wandering test reading mean?
If a continuity reading will not settle, look for an intermittent joint or a poor test connection. The test connection is checked and the test repeated before the circuit is blamed.
Q5How does insulation resistance help with a fault that comes and goes?
Readings change with temperature and damp, so they are taken under recorded conditions and trended against the baseline. A low value, or one that keeps falling from test to test, points to moisture, damage or ageing, often before a hard fault appears.
Q6Can an intermittent fault be tested on a live circuit?
No. Tests are made de-energised, with the circuit isolated, locked out and proved dead. ATC is told first, and a primary connector is never separated on an energised loop. Once the suspected section is repaired it is retested and the result recorded.
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