Electrical Wiring
Electrical Wiring
This domain examines domestic and small-industrial wiring systems, cable-size selection, control circuits and compliance with IS 732 and the Central Electricity Authority safety regulations.
Core rules
- Systems: cleat, casing-and-capping, batten and conduit (surface or concealed). Concealed conduit is standard in modern construction; conduit fill should not exceed about 40%.
- Typical copper sizes: 1.0 and 1.5 mm² for lighting, 2.5 and 4 mm² for power sockets, 6 mm² for sub-mains.
- Colour convention: older Indian practice uses red, yellow and blue for phases, black for neutral and green for earth; harmonised IS 732 practice uses brown, black and grey with blue neutral and green-yellow earth.
- A switch must be in the phase conductor, never in the neutral.
- Two-way switching uses two two-way switches with three-core strapping between them for staircase control.
- Socket outlets need a continuous protective earth, sized with the phase conductor.
- Switchboards are normally fixed about 1.2–1.35 m above floor level.
Worked example
A lighting sub-circuit feeds five 60 W lamps at 230 V. Find the current and select a protective device. Total load = 5 × 60 = 300 W; I = 300/230 = 1.30 A. A 1.5 mm² copper conductor (roughly 14–16 A in conduit) with a 6 A MCB is adequate and gives discrimination against the 16 A socket circuit. Do not fuse a lighting circuit at 16 A merely because the cable can carry it.
Traps that cost marks
- Wiring the switch into the neutral, leaving the holder live when switched off.
- Omitting the earth to a metal luminaire or socket.
- Selecting cable by current alone, ignoring voltage drop over a long run.
- Mixing old and new colour codes in one answer without stating which convention is used.