A situation on site, a set of readings, and a judgement to make. You commit to an answer before you see the reasoning, which is the only way this kind of thing is any use.
These are not multiple-choice trivia. They are pitched at electricians, engineers, and apprentices who want to test their real-world diagnostic judgement against the regulations. The answer matters less than the explanation underneath it, and every one of them points back to the guide, calculator or Visual Lab where the underlying idea is set out properly.
Inspection and testing
8 scenarios
Readings that do not add up. A ring with one socket out of step, a Zs that passes the table and fails in service, insulation resistance on a circuit full of electronics.
EICR defect coding
8 scenarios
The same defect coded C1, C2, C3 or FI depending on what is around it. A plastic board under the stairs, a borrowed neutral, a locked board you agreed to inspect.
Fault finding
8 scenarios
Symptom to cause. A Zs four times too high with a perfect line to neutral reading, an RCD that trips at busy times, a motor that hums and will not turn.
Apprentice Diagnostic Challenge
5 scenarios
City & Guilds 2391/2396 interactive fault simulations. Calibrated MFT test readings, statutory citations, and instant step-by-step scoring.
What is coming
Two more sets are being written and checked: design and protection decisions, and the physics behind some common misconceptions. Every regulatory claim is verified against a source before a set goes up, which is the slow part and the reason they arrive one at a time rather than all at once.