What is ELCB and the advantages of ELCB?

What is ELCB?

  • ELCB stands for Earth Leakage Circuit Breaker. It is designed to prevent shock due to earth leakage.
  • It is designed to turn off the electricity if any leaking in electricity to the earth occurs.
  • ELCB is also known as RCD (Residual Current Device)


What is earth leakage?

Earth leakage is the flow of electrical current from a live conductor to the earth via an unintended path. It may flow between their inadequate insulation or through a person’s body, resulting in electrical shock. If the leakage current exceeds 30mA, the result of an electrical shock can be fatal. When such current leakage is detected, protection devices are used to disconnect the power source.

Operation of ELCB

An electrical circuit breaker is a type of latching relay that has the main supply of buildings connected through its switching contacts so that when earth leakage is detected, the circuit breaker will disconnect the power. The fault current from live to the ground wire in the fitting it protects can be detected using this. If sufficient voltage is applied across the circuit breaker’s sense coil, it will shut down the power and remain off until physically reset. Fault currents are not detected by an ELCB that is used for voltage sensing.

Purpose of ELCB

The main function of an earth leakage breaker or ELCB is to prevent electric shock when electrical installations pass through high-ground impedance as they are safety devices. These circuit breakers detect small stray voltages on top of metal-enclosed electrical equipment and break the circuit when hazardous voltages are detected. The main purpose of ELCB is to prevent harm to people and animals due to electric shock.

Construction of ELCB

Every electronic device should be earthed in accordance with international standards. It will eliminate the risk of electrocution. We must bury a metallic rod deep in the soil, with an ELCB connected between the wire coming from the rod and the wire attached to the external metallic body of the electric device, or the ELCB is connected to the earth wire.

Types of ELCB

Based on Operation

Voltage ELCB

Current ELCB

Voltage ELCB

Voltage ELCBs were in full-size use on the grounds that then, and plenty of are nevertheless in operation however are now not set up in new construction. Voltage Controlled ELCBs detect the potential for upward impact between a covered interconnected metal structure (system frame, conduit, housing) and a remote ground reference electrode. They function at a detected capability of around 50 volts to open the primary breaker and isolate the delivery from the covered premises.

We can connect remote reference earth connection by using a second terminal in voltage-operated ELCB.

Working Principle

One of the relay coil’s terminals is directly connected to the earth, while the other is connected to the equipment’s body. The coil detects the voltage difference between the earth and the equipment’s body.

A voltage difference appears across the terminals of the coil if the live wire breaks or its insulation fails and comes into contact with the body of the equipment. As a result, the current begins to flow through the coil, and it becomes energized. The relay begins to produce electromagnetic force. When the current exceeds a certain threshold, the relay generates enough force to pull the latch. The latch break opens the contacts, disconnects the power supply to the equipment, and prevents electrical shock.


  • Protect from electrical shocks
  • Less sensitive
  • Don’t trip unnecessarily


  • It can’t sense leakage (current) to any other earthed body from phase
  • Need extra connection
  • Cannot sense low leakage current

Current ELCB

RCD/RCCB is the most common type of ELCB. An RCCB is typically made up of a current transformer with several primary windings and one secondary winding. The primary windings are neutral and line wires (or lines in multiple phase systems). The secondary winding is a wire-wound coil. The current through the secondary winding is zero at the balanced condition. In the balanced condition, the flux caused by the current flowing through the phase wire is neutralized by the current flowing through the neutral wire, because the current flowing from the phase is returned to the neutral.

When a fault occurs, a small current flows to the ground as well. This causes a current imbalance between the line and neutral currents, resulting in an unbalanced magnetic field. This causes a current to flow through the secondary winding, which is linked to the sensing circuit. This will detect the leak and send a signal to the tripping system.

Working Principle

The operation of the current ELCB or RCCB is based on the current imbalance between the phase and neutral conductors. Continuous monitoring of phase and neutral currents. Under normal conditions, the phase and neutral currents are the same because the same current flows in the load. When the current flows in an unintended path, the neutral current decreases, resulting in an imbalance. When the imbalance exceeds a certain limit, the display opens its contacts and turns off the power.

The RCCB operates on the principle of Kirchhoff’s Current Law, which states that the amount of current entering the load through the hot wire must equal the amount of current leaving the load through the neutral wire. The difference between the two currents, known as the residual current, must be zero. If there is a difference, the current will flow somewhere and an imbalance will occur.

The RCCB contains a zero-sequence current transformer with three coils: a phase coil, a neutral coil, and a search coil. It is used to detect an imbalance or difference between two currents. The phase coil and the neutral coil are wound on a toroidal core in such a way that they compensate for each other’s currents.

If the currents are the same, the resulting fluxes cancel each other out and there is no induced current in the search coil as in normal conditions. Assuming there is a leakage current, the current difference creates a magnetic flux that induces a voltage in the search coil. As the search coil is connected to the relay trip mechanism, the contacts open and the load is de-energized.


  • RCCB cuts the current flow when current leaks occur from any circuit’s part
  • Reliable and more sensitive
  • No need for earth connection


  • Do not provide safety from short circuit current
  • Expensive
  • It trips unnecessarily due to the high sensitivity

Types based on Poles

  • 2-Pole ELCB:
  • 3-Pole ELCB:
  • 4-Pole ELCB:

2-Pole ELCB:

It has two terminals for both ingoing and outgoing for the phase and neutral connections and it is mainly used to give protection of a single-phase system.

3-Pole ELCB: 3 pole ELCB is used to protect the three-wire three-phase system and it consists of three incoming and three outgoing terminals.

4-Pole ELCB: Four pole ELCB is used to protect the four-wire three-phase system

Internal parts of ELCB


What are the replacements for ELCB?

Fuse, MCCB, RCCB, ELCB are the main alternatives to MCB

Fuse: Fuse is an electrical device that is designed as a current interrupting device that opens or breaks the circuit by fusing the element in the circuit when current exceeds a certain value.

MCB: MCB stands for Miniature Circuit Breaker

MCCB: MCCB stands for Moulded Case Circuit Breaker.

RCCB: RCCB stands for Residual Current Circuit Breaker.