Purpose and History of Earth-leakage Circuit Breakers
– Prevents injury to humans and animals from electric shock
– Protects instruments, circuits, and operators from earth leakage
– Detects faults or shocks to metalwork connected to the circuit ground
– Ensures the level of protection intended for the installation
– Eliminates confusion in the electrical industry by using the term ‘residual current device’ (RCD)
– Early ELCBs were voltage operated devices (VO-ELCB)
– Current sensing devices (RCD/RCCB) replaced voltage operated devices
– Voltage sensing ELCBs were introduced about sixty years ago
– Current sensing ELCBs were introduced about forty years ago
– IEC decided to apply the term ‘residual current device’ (RCD) to differential-current-operated ELCBs
Operation and Types of Earth-leakage Circuit Breakers
– ELCB is a latching relay that disconnects power when earth leakage is detected
– Detects fault currents from live to the Earth wire within the installation
– Switches off power when sufficient voltage appears across its sense coil
– Remains off until manually reset
– Voltage-sensing ELCB does not sense fault currents from live to any other Earthed body
– Voltage operated ELCB (referred to as ELCB)
– Current operated ELCB (referred to as RCCB)
– Voltage operated ELCBs are no longer installed in new construction
– Current sensing devices (RCD/RCCB) are commonly used
– RCCB consists of a current transformer with multiple primary windings and one secondary winding
Earth Bypassing in ELCBs
– ELCB protected installations may have unintentional connections to Earth
– Fault current may pass to Earth without being sensed by the ELCB
– Operation of the ELCB is not compromised in these situations
– ELCB continues to prevent Earthed metalwork rising to a dangerous voltage
– Higher fault current is needed to reach the same voltage level for power cutoff
Causes of Nuisance Trips in ELCBs and RCDs
– High Earth leakage current in neighboring buildings can cause voltage difference and trip the ELCB
– Close Earth rods are unsuitable for ELCB use
– ELCBs are prone to nuisance trips from normal Earth leakage
– ELCBs have less well-developed filtering against nuisance trips compared to RCDs
– RCD nuisance trips are more common than ELCB nuisance trips
– Lowered insulation resistance in older equipment or buildings in damp conditions
– Burden currents from multiple sources can accumulate and reduce the tripping level
– ELCBs with a 30 mA protective device may trip at 20 mA due to burden currents
– Nuisance tripping was more common in past installations with single ELCBs protecting multiple circuits
– Heating elements filled with fine powder can absorb moisture and cause nuisance tripping
Factors Affecting ELCB Performance
– Some ELCBs do not respond to rectified fault current
– Older ELCBs are more likely to have fault current waveforms they won’t respond to
– ELCBs and RCDs should be periodically tested to ensure they still work
– Disconnection of Earth wires from the ELCB can prevent proper tripping and grounding
– ELCBs and RCDs are mechanical devices prone to failures
– Importance of proper Earth rod placement
– Earth rod placement close to neighboring buildings can cause nuisance trips
– High Earth leakage current in other buildings can raise local ground potential
– ELCBs are inherently immune to some causes of false trips suffered by RCDs
– Close Earth rods are unsuitable for ELCB use
– Real-life installations sometimes encounter close Earth rod placements
– Impact of environmental conditions on ELCBs
– Prolonged damp and rain conditions in tropical areas can lower insulation resistance
– Moisture tracking can cause insulation resistance to lower in wiring
– Older equipment or equipment with heating elements are more prone to nuisance trips
– Unused heating elements in tropical areas can absorb moisture and cause tripping
– Brand new equipment can also experience tripping due to moisture absorption. Source: https://en.wikipedia.org/wiki/Earth-leakage_circuit_breaker
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An earth-leakage circuit breaker (ELCB) is a safety device used in electrical installations with high Earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected. Once widely used, more recent installations instead use residual-current devices (RCDs, RCCBs or GFCIs) which instead detect leakage current directly.
