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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Earthing is necessary to give protection against
Danger of electric shock
Voltage fluctuation
Overloading
High temperature of the conductors
Danger of electric shock
Quick Summary: Earthing provides a low-resistance path to the ground for fault currents, ensuring that the metallic enclosures of electrical equipment remain at zero potential. This prevents the flow of dangerous currents through the human body in the event of an insulation failure or short circuit to the frame.
Earthing provides a low-resistance path to the ground for fault currents, ensuring that the metallic enclosures of electrical equipment remain at zero potential. This prevents the flow of dangerous currents through the human body in the event of an insulation failure or short circuit to the frame.
Ishock=RhumanVtouch — Current flowing through the human body during a fault
Vtouch=Ifault×Rearth — Potential rise of the metallic frame during a fault
When insulation failure occurs, the metal body of the device becomes live. Without earthing, touching the body completes the circuit through the human body (Rhuman≈1000Ω−5000Ω) to the earth, leading to shock. With an effective earthing system, the fault current flows through the earth wire (Rearth<1Ω), tripping the protective devices like MCB or ELCB, thereby isolating the circuit.
The primary objective of earthing is human safety and equipment protection.
The resistance of the earthing path must be kept as low as possible to ensure the quick operation of protective devices.
Neutral earthing (system earthing) is different from equipment earthing (safety earthing).
Earthing prevents the accumulation of static charges on non-current-carrying metal parts.
Protects equipment from high voltage surges.
Provides a stable reference potential for electronic circuits.
Ensures immediate tripping of fuses or circuit breakers during short-to-frame faults.
Requires regular maintenance and periodic testing of electrode resistance.
Corrosion of earth electrodes can increase resistance over time.
Domestic wiring and appliances (fridges, washing machines).
Industrial motor frames and switchgear assemblies.
Lightning protection systems for buildings.
Option B (Voltage fluctuation) is managed by voltage stabilizers or AVRs.
Option C (Overloading) is managed by MCBs, MCCBs, or overload relays.
Option D (High temperature) is managed by proper ventilation or appropriate cable sizing (current carrying capacity).
A is correct — Earthing is explicitly designed to prevent the risk of electric shock by maintaining the potential of exposed conductive parts at zero level relative to the ground.
Always remember that earthing protects the user from current, while fuses/breakers protect the equipment from excess current (overload/short-circuit).