The Earth Leakage Circuit Breaker (ELCB) is a safety device used in electrical devices with high ground impedance to prevent electric shock.
The ELCB used to directly detect currents leaking to earth from an installation and interrupt the power supply.
Once widely used, recent installations have changed to using residual current devices (RCD, RCCB or GFCI), which directly detect leakage current.
what is the purpose of elcb?
The main purpose of the earth Leakage Circuit Breaker (ELCB) is to prevent people or animals from being injured by electric shocks and fires that are caused by short circuits.
What types of ELCB are available?
There are two types of ELCB
- Voltage operated (Voltage ELCB).
- Current operated (Current ELCBor RCD, RCCB).
Voltage Earth Leakage Circuit Breaker
Voltage ELCB is a voltage operated circuit breaker, it has been widely used, many are still operating, but are no longer installed in new buildings.
The voltage ELCB contains a relay coil, one end of the coil is connected to the metal body and the other end is grounded.
The voltage operated ELCB detects the potential rise between the protected interconnected metal products (equipment frame, conduit, enclosure) and the remotely isolated ground reference electrode.
They operate at a detected voltage of approximately 50 volts to open the main circuit breaker and isolate the power supply from the protected area.
If the voltage of the device body rises due to the insulation failure of the device or contact with metal parts, the difference between the ground voltage and the body load voltage may result, and the risk of electric shock may occur.
Compared with current ELCBs, voltage ELCBs have several disadvantages as below:
- A broken wire in the fault to the load part or the ground part will cause the ELCB to fail to operate.
- An additional third wire from the load to the ELCB is required.
- Separate equipment cannot be grounded separately.
- Any additional connection to the earth on the protected system may disable the detector.
- ELCB can sense equipment failure and cannot detect whether a humans accidentally touched the live part of ELCB.
Current Earth Leakage Circuit Breaker
The current ELCB type is a circuit breaker that is commonly used. It is also called RCD (Residual Current Device) or RCCB (Residual Current Circuit Breaker), The Product Reference of TORD4-63 type.
RCD/RCCB usually consists of a current transformer with multiple primary windings and one secondary winding. Under balanced conditions, the current through the secondary winding is zero.
Under balanced conditions, the magnetic flux due to the current passing through the phase wire will be neutralized by the current passing through the neutral wire because the current flowing from the phase wire will return to the neutral wire.
When a fault occurs, a small current will also flow to the ground.
This makes the unbalance between the line and the neutral current produce an unbalanced magnetic field.
This induces current in the secondary winding connected to the sensing circuit. This will detect leaks and send a signal to the trip system.
- The VoltageELCBs are less sensitive to fault conditions, and therefore have fewer nuisance trips
- The Voltage ELCBscan trip when a DC current fault is grounded, but the RCD/RCCB of the transformer interface cannot sense the ground fault.
- And the frequency is significantly higher than the frequency of the power supply.
- The currentELCBs is not affected by parallel grounding.
What is the application scenario of ELCB?
- The voltage operation ELCBis usually used in places with poor grounding conditions (this kind of ELCB is rarely used now)
- The currentoperated ELCB is a popular circuit breaker used in industrial, commercial and household applications.