The IET Guidance Note 3 sets out the items the visual inspection must cover. They fall into clear categories.
Switchgear and distribution. Consumer units, distribution boards and main switches. Protective devices present and in good order: fuses, MCBs, RCDs, RCBOs. Correct ratings against the circuits they protect. Sound busbars, connections and terminations. Clear circuit labelling. Adequate working space.
Wiring systems. Cable condition, sheathing and insulation. Correct support and fixing at appropriate intervals. Mechanical protection where required. Cables in the correct zones when buried in walls. Containment, conduit and trunking in good order. The right type of cable for the environment, such as heat-resistant cable near heat sources. Any sign of overheating: discolouration, melting, burn marks.
Accessories. Sockets, switches and connection units undamaged and securely fixed. The right accessory for the location, including an appropriate IP rating in bathrooms. Correct polarity evident where identifiable at accessory level. Covers and blanks fitted, no exposed terminals.