Electrical Wiring, Cables and Accessories
What is tested
Selection of a wiring system, cable size, colour code and accessory rating for domestic and small workshop installations, referred to IS 732 and the IE Rules, 1956.
Wiring systems
Cleat, casing-and-capping, batten, and conduit (PVC or GI), with concealed conduit preferred for neat domestic work and GI conduit for damp or industrial areas. Concealed runs normally use 20 mm conduit for lighting and 25 mm for power, with draw boxes at every bend or every 90°. Conduit fill should not exceed about 40% of the internal cross-section, otherwise wires cannot be drawn later.
Colour code
Under IS 732: phases brown, black, grey; neutral blue; protective earth green-yellow. Older installations use red, yellow, blue for phases, black for neutral and green for earth. Examiners test both codes.
Cables and ratings
House wiring uses PVC single-core copper of 1.0, 1.5, 2.5, 4 and 6 mm². Approximate safe currents: 1.0 mm² - 11 A, 1.5 mm² - 14 A, 2.5 mm² - 20 A, 4 mm² - 26 A. Lighting circuits take 1.5 mm² with a 6 A device; 16 A power sockets need 2.5 mm² or larger.
Worked example
A 10 A load at the end of a 20 m run of 2.5 mm² copper, ρ = 0.0172 Ω·mm²/m. Drop = 2 × I × L × ρ / A = 2 × 10 × 20 × 0.0172 / 2.5 = 2.75 V, which is 1.2% of 230 V and acceptable, since IS 732 keeps a final circuit within roughly 3%.
Traps
Confusing earth green-yellow with neutral; sizing by current alone and ignoring voltage drop on long runs; and forgetting a two-way switch needs two strappers plus a common.