Wiring Systems
What the exam tests
This domain tests wiring methods, cable selection, colour identification, conduit practice, voltage drop and inspection of domestic wiring.
Core rules
- Common systems include cleat, casing and capping, batten, surface conduit and concealed conduit. Concealed conduit gives mechanical protection but must be continuous and accessible at boxes.
- Choose cable by current-carrying capacity, voltage drop, ambient temperature, grouping and protective device rating. The protective device rating must not exceed the cable capacity.
- Earth continuity must be maintained to every socket and metal enclosure. Joints belong in accessible boxes, not buried in conduit.
- Common Indian practice uses red, yellow and blue for phases, black for neutral and green for earth; harmonised cable may use brown, blue and green-yellow. Confirm by schedule and never rely on colour alone.
Worked example
A 2 kW heater at 230 V draws 8.7 A. It is 20 m from the board on 1.5 mm² copper. Using ρ = 0.0175 Ω mm²/m for the go-and-return path: drop = 2 × 0.0175 × 20 × 8.7 / 1.5 = 4.06 V, about 1.8% of 230 V. This is acceptable, but the cable must also have a current rating above the 10 A MCB rating.
Traps
Do not use earth as a neutral. Do not join cables with tape inside a conduit. Do not choose cable only by load current and ignore voltage drop on long runs. Do not assume colour alone proves phase, neutral or earth; test and label.