Previous Year Question
Correct answer: C
Explanation
C — Electric shock. Protective earthing bonds exposed conductive parts to a fault-current path and works with automatic disconnection to reduce shock risk.
Formula
Step-by-step solution
Correct answer: C — Electric shock
What happens when insulation fails
The metal enclosure of electrical equipment is normally isolated from live conductors. If insulation fails and a live conductor touches the enclosure, the metal can become energized. A person touching it while in contact with earth or another conductive surface may then complete a dangerous current path.
Protective earthing connects exposed conductive parts to the protective-conductor system. During a fault, this connection provides a designed path for fault current and helps limit hazardous potential differences. Suitable protective devices then disconnect the faulty circuit.
The exact disconnection mechanism depends on the earthing arrangement. A sufficiently low fault-loop impedance may allow a fuse or circuit breaker to operate promptly. In arrangements where earth-path impedance limits current, residual-current protection is particularly important. Earthing and the protective device must therefore work together.
Bonding also reduces differences of potential between simultaneously accessible conductive parts. Earthing does not guarantee that an equipment body stays at exactly zero volts during every fault, and it does not replace correct insulation or circuit protection. Its principal safety purpose in this question is to prevent or reduce electric-shock danger from exposed metal becoming live.
Other options
A harmonics require filtering/power-quality measures. B voltage fluctuations require regulation/system control. D overload is handled by overcurrent/thermal protection. C is the direct safety purpose of protective earthing.
Common mistake
Saying earthing prevents overload. It protects against dangerous exposed-conductive-part voltage during earth faults.
Exam tip
Ask: ‘What happens if a live wire touches the metal body?’ Earthing provides the protective fault path.
Quick method
Equipment earthing → body protection from shock.