Earth Leakage Circuit breaker (ELCB) is a special kind of circuit breaker . it is a safety device used to avoid shock with high earth impedance. It detects small stray voltage on the metal enclosure. If a dangerous voltage detected, it interrupts the circuit current.
The ELCB detects the voltage, the same device used which can detect the current, that known as the (Residential current circuit breaker) RCCB or (Residential current device) RCD.
Operation of Earth Leakage Circuit breaker (ELCB)
Earth Leakage Circuit Breaker (ELCB) is a special type of latching relay. The main power supplied through the switching device of ELCB. If it detects unsafe conditions, the switch contact detached and power interrupted.
Within the installation it protects, the ELCB detects fault current from life to an earth wire. (voltage ELCB cannot detect the fault current) It will switch off the power if sufficient voltage appears across the ELCB’s sense coil.
It cannot restart automatically and remains off until manually reset.
Types of ELCB
There are two types of ELCB.
- Voltage operated ELCB
- Current operated ELCB
1) Voltage operated ELCB
Previously, the voltage-operated ELCB widely used and is still in operation. But it is not favorable for new construction.
It detects the voltage rise in potential between the protected interconnected equipment enclosure and isolated earth electrode. It operates when the potential around 50V and opens the main breaker.
And it isolates the equipment from the supply. The main power to the equipment interrupted.
It has the second terminal for connecting to the remote reference earth connection.
The earth is different when an ELCB is used. The earth rod connected through the ELCB by connecting its two terminals. One terminal connected to the installation earth CPC (circuit protective conductor, earth wire), and the other to the earth rod.
The voltage at the trip coil is zero in the balanced condition. And the voltage is more than 50V it will operate. The operating voltage is depending on the load (application).
Advantages of voltage-operated ELCB
- It is less sensitive to the fault current. Therefore, it has fewer nuisance trips.
- ELCB can be arranged to protect against cable damage and not trip on faults in downline installations.
- Voltage sensing ELCB will trip on DC current fault to ground. This fault cannot be sensed by the transformer interfaced with RCD/RCCB. These similar issues with frequencies significantly above the main frequency.
- ELCB is necessary for a second connection. And the opportunity that extra connection to ground on the threatened system can inactivate the detector.
Disadvantages of voltage-operated ELCB
- ELCB adds extra resistance and an extra point of failure in the earthing system.
- It can trip by other external voltage connected to the earth system.
- ELCB cannot detect the fault which is not passing through the CPC to earth rod.
- It may malfunction by electrically leaky appliances like a water heater, geyser, and washing machine when it used with RCD.
- Earthing system used a mutual earth rod. Therefore, it is not possible to divide into many sections with independent error protection. So, at times of fault, the entire building will isolate and it is not possible to isolate one part of the system.
2) Current operated ELCB
Current sensing ELCB known as the RCCB/RCD. It consists of a CT (Current transformer).
This CT has multiple primary windings and one secondary winding. Neutral and line wires connect with the primary winding. The secondary winding is a wire-wound coil.
A balanced condition, the current through the secondary winding is zero. The current flows from the phase will be returned to the neutral, hence the flux produced due to phase wire is neutralized by the flux produced due to the neutral wire.
When the fault occurs, it makes an unbalance between the neutral and lines current. And this creates an unbalance in magnetic flux. This induces a current through the secondary winding.
A sensing element connected at the secondary winding. This will sense the leakage and send a signal to the tripping system.
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