Domestic and Industrial Wiring Installation
This domain tests installation design: how a building or plant is split into circuits, protected, earthed and documented.
Domestic design
- Divide the installation into sub-circuits from the main board: lighting/fan circuits, 16 A power circuits, and dedicated circuits for air-conditioners, geysers and motors.
- Calculate connected load, apply a diversity factor, then size the main switch, cable and protective devices. A flat with 3 kW lighting and 6 kW power load, at 0.6 diversity, needs about 5.4 kW - a 25–32 A main.
- Provide a DP MCB/RCCB incomer, separate neutral and earth busbars, and never loop neutrals between circuits.
- Use two-way switches for staircase lighting, intermediate switches for three or more control points, and godown wiring for long corridors.
Industrial installation
- Feed motors from MCC feeders combining MPCB, contactor and overload relay; run power in cable trays and lighting in conduit.
- Separate power cables from signal and instrumentation cables to reduce interference.
- Earth the panel body, doors and cable trays; use braided straps across hinged doors.
- Label every circuit at both ends and update the single-line diagram after any modification.
Worked example
A workshop has 6 × 1.5 kW motors and 2 kW of lighting. Motor demand at 0.7 diversity = 6.3 kW; total 8.3 kW at 0.8 PF gives I = 8300/(1.732 × 415 × 0.8) ≈ 14.4 A, so a 32 A MCCB incomer with a 10 mm² copper feeder leaves margin for starting surge and future load.
Traps
- Switch placed in the neutral instead of the phase.
- One RCCB protecting everything, so a single earth fault blacks out the whole building.
- Lighting and power points mixed on one 6 A circuit.
- No spare ways or spare capacity left in the distribution board.