Domestic Wiring Systems
What this domain tests
Domestic Wiring Systems tests the choice and layout of wiring systems, subcircuits, distribution boards and earthing in houses, using IS 732 principles and Indian practice.
Core rules
- Common systems are cleat, batten, casing-and-capping, and conduit (surface or concealed). Conduit gives mechanical protection and allows rewiring; casing-and-capping is easier for surface work.
- A domestic installation is divided into subcircuits: lighting, 16 A power sockets, geyser, air-conditioner, and so on. Each subcircuit has its own MCB at the DB.
- Use 1.5 mm² for lighting, 2.5 mm² for 16 A socket circuits, and 4.0 mm² for geysers and air-conditioners, with protective devices matched to the cable.
- Keep conduit fill within about 40% of the inner area; do not bury joints in conduit. Joints belong in accessible boxes.
- Standard mounting heights are about 1.2 m for switches and 1.3 m for sockets, unless the design says otherwise.
- Earthing is mandatory for metal enclosures and appliance bodies. Use a separate earth conductor, not the neutral.
Worked example
A two-bedroom flat has a 6-way DB. Lighting: 1.5 mm², 6 A MCB. Bedroom sockets: 2.5 mm², 16 A MCB. Geyser: 4.0 mm², 16 A MCB with a 30 mA RCCB. The earth wire runs from the DB earth bar to every socket and metal fitting, and the electrode resistance is measured and recorded.
Traps that cost marks
Using the neutral as an earth; hiding a joint inside conduit; installing a 16 A socket on 1.5 mm² wire; and omitting a separate circuit for a geyser.