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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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Which protective device will not operate due to over-current?
Fuse
MCB
ELCB
MCCB
ELCB
An Earth Leakage Circuit Breaker (ELCB) is specifically designed to detect leakage currents flowing to the ground, which typically occur due to insulation failures. Unlike MCBs, MCCBs, or fuses, it is not configured to respond to over-current or short-circuit conditions, as those are handled by thermal or magnetic tripping mechanisms not present in standard ELCBs.
An Earth Leakage Circuit Breaker (ELCB) is specifically designed to detect leakage currents flowing to the ground, which typically occur due to insulation failures. Unlike MCBs, MCCBs, or fuses, it is not configured to respond to over-current or short-circuit conditions, as those are handled by thermal or magnetic tripping mechanisms not present in standard ELCBs.
Iresidual=Iphase−Ineutral — The leakage current detected by the ELCB
Φnet=Φphase−Φneutral — The residual flux in the sensing core
The ELCB operates on the principle of flux balance. It uses a core transformer (zero sequence current transformer) to monitor the current in the phase and neutral conductors. Under normal operation, the vector sum of currents is zero; if a leak occurs, the imbalance in current creates a residual flux that triggers a relay to break the circuit.
ELCB is a safety device for ground leakage detection.
It detects very small leakage currents (often 30mA).
It provides protection against electric shock.
MCB/MCCB provide protection against overload and short circuit.
Provides protection against electric shock
Detects dangerous insulation leakage to earth
Does not protect against over-current or short circuits
Needs a proper ground connection for effective operation
Residential wiring for safety
Portable electric equipment
Water heaters and appliances
| Feature | MCB | ELCB |
|---|---|---|
Protection Type | Over-current | Leakage Current |
Modern installations prefer RCDs (Residual Current Devices) over voltage-operated ELCBs for better reliability.
Option A, B, and D are all protective devices that rely on thermal or magnetic effects to clear high current faults (overloads/short circuits).
C is correct — ELCB is specifically designed for leakage current detection and not for over-current protection.
Remember that fuses and MCBs protect the 'equipment/circuit' from high currents, while ELCBs/RCCBs protect 'human life' from current leakage.