Electrical Wiring
Scope
The exam tests selection and layout of wiring systems to IS 732 and conductor specification to IS 694: cleat, casing-and-capping, batten, surface conduit and concealed conduit. Questions often ask which system suits a given location and what limits apply to a subcircuit.
Core rules
- A lighting subcircuit: maximum 10 points and 800 W, wired in 1.0 or 1.5 mm² copper, protected at 6 A.
- A power subcircuit for 6 A/16 A sockets uses 2.5 mm² copper protected at 16 A; heavy appliances such as geysers and air-conditioners get dedicated circuits.
- Conduit fill must not exceed about 40% of the internal area; bends must be swept, not kinked, and draw boxes provided on long runs.
- Old Indian colour code: red, yellow, blue phases; black neutral; green earth. New code: brown, black, grey phases; blue neutral; green-with-yellow earth.
- The switch must be in the phase conductor, never in the neutral. Every circuit must carry a continuous earth continuity conductor.
Worked example
A bedroom has 6 × 60 W lamps, 2 × 70 W fans and one 6 A socket. Lighting load = 360 + 140 = 500 W, current at 230 V = 2.17 A, and the lighting points number 9 - within the 800 W/10-point limit, so a 1.5 mm² lighting subcircuit at 6 A is acceptable. The socket must not be added to this circuit: it belongs on a 2.5 mm², 16 A power subcircuit. Adding 6 A socket load would take the lighting circuit to 1,880 W and overload the 1.5 mm² conductor.
Traps that cost marks
Switching the neutral, omitting the earth to lighting points, using 1.0 mm² for power, and running joints inside conduit. Concealed conduit must be laid before plastering and tested for continuity before the wiring is drawn in.