Practical Assessment and Fault Diagnosis
Core concepts
Know a systematic approach to fault finding: gather information, confirm the symptom, form a hypothesis, test logically, and verify the repair. Understand common faults: open circuits, short circuits, earth faults, high resistance joints, and intermittent faults. Be familiar with safe testing techniques, use of appropriate instruments, and the importance of restoring and retesting after repair. Recognise the value of documentation, circuit diagrams and previous test results.
Traps in questions
Traps include replacing components without diagnosing the cause, testing live when dead testing would answer the question, and failing to re-verify after a repair. Watch for scenarios where a symptom (e.g. tripping RCD) is assumed to be a single cause without testing. Another trap is ignoring the need to record and communicate findings.
Worked example / rule of thumb
If an RCD trips, isolate and test insulation resistance on each circuit in turn to locate the faulty circuit, then inspect for damaged cable or moisture ingress. Rule of thumb: divide and conquer - split the installation into sections and test each to localise the fault before repairing. Always retest and document.