Competency 8: think in halves. If half the house is dead, look at the board, not the far socket. Split the circuit, test at the midpoint, and you halve the search each time. The three classic faults each have signatures: open circuit (no volts downstream), short circuit (breaker trips instantly on reclose), earth leakage (RCD trips, loads work on a circuit-by-circuit basis). Document every repair — the record is your professional signature.