Electrical Wiring, Installation, Protection and Earthing
Electrical Wiring, Installation, Protection and Earthing
This domain tests selection and installation of cables, switches, protective devices and earthing as applied to PV AC and DC circuits.
Core rules
- Indian flexible cable colour code: phase red/yellow/blue, neutral black, earth green or green-yellow.
- Protective devices: fuse, MCB (overload/short circuit), MCCB (larger ratings), RCCB/ELCB (earth leakage, typically 30 mA for shock protection).
- RCCB does not protect against overload; MCB does not protect against earth leakage.
- Earthing limits touch voltage and provides a fault path; earth resistance should be low, commonly ≤1 Ω for substations and a few ohms for installations, checked with an earth tester.
- Cables must be sized for current-carrying capacity, voltage drop and derating for temperature/grouping.
Worked example
A 2 kW, 230 V load draws 8.7 A. A 16 A MCB is selected as the next standard rating above the load. A 2.5 mm² copper cable with a tabulated capacity of about 21 A in conduit is suitable, but the voltage drop must be checked: for 20 m run, mV/A/m value 18, drop = 18 × 8.7 × 20 / 1000 = 3.13 V, about 1.36% of 230 V, acceptable if the limit is 3%.
Traps that cost marks
Putting a fuse or switch in the neutral only; using the earth wire as a current-carrying conductor; selecting cable by load current alone; assuming an RCCB trips on overload; mixing AC and DC ratings on DC circuits.