Wiring, Cabling and Accessories
What this domain tests
Wiring, Cabling and Accessories covers domestic circuit design, conductor selection, protective devices, earthing, colour code and installation accessories such as switches, sockets, MCBs and distribution boards.
Core rules
- Follow IS 732 principles: divide the installation into lighting, power and fixed-appliance circuits; protect each with a suitable MCB; use a 30 mA RCCB for socket outlets and wet areas.
- Typical copper sizes are 1.0–1.5 mm² for lighting, 2.5 mm² for socket circuits and 4.0 mm² for high-load fixed appliances, but the final choice depends on current-carrying capacity, grouping, ambient temperature and voltage drop.
- Standard colours are brown for phase, light blue for neutral and green-yellow for protective earth. Older installations may use red, black and green; identify and label rather than guess.
- Switch the phase, not the neutral. Use a double-pole isolator for a geyser. Keep joints in accessible boxes, not buried in conduit. Earth every metal enclosure.
- Avoid overloading a circuit by adding sockets to an existing lighting circuit.
Worked example
A 3000 W fixed heater at 230 V draws I = 3000/230 = 13.0 A. A 16 A MCB is appropriate only if the chosen cable has a current-carrying capacity above 16 A after derating. A 2.5 mm² copper PVC cable clipped direct is commonly adequate, but a long run needs a voltage-drop check. The heater body must be earthed, and the isolator should be double-pole and accessible.
Traps that cost marks
Fitting a 32 A MCB to protect a 1.5 mm² cable; using the earth wire as a neutral; switching the neutral instead of the phase; making concealed joints; and assuming a socket outlet is protected by an RCCB when it is not.