ELCB Working Principle, Construction, Full form, Types

Electrical safety is the main aim of any residential or commercial electrical installation. To prevent electrical shocks and identify insulation failures of electrical appliances, the ELCB full-form Earth Leakage Circuit Breaker is used. Generally, ELCBs are available in different ratings 16A,32A, 40A, and 63A, and sensitivity like 30mA, 100mA, and 300mA.

This device detects stray voltages on metal enclosures of equipment and interrupts the circuit when dangerous voltages are detected.

In this article, we will discuss, the working principle and construction of ELCB, types and their advantages in electrical circuits.

What is an Earth Leakage Circuit Breaker (ELCB)?


An Earth Leakage Circuit Breaker, also known as an ELCB, is a safety device used in electrical circuits. Its primary function is to prevent electric shocks by detecting small stray voltages on the metal enclosures or body of electrical equipment.

When a dangerous voltage is detected, the ELCB breaks the circuit and protects the individual who is come in contact with a live circuit.

ELCBs are designed to detect current leaks and insulation failures in electrical circuits. By monitoring the flow of current, they can quickly identify any abnormalities and protect against potential hazards.

Working Principle of ELCB

There are two main types of ELCBs:

  • Voltage operated ELCB
  • Current operated ELCB

Voltage Earth Leakage Circuit Breaker

The working principle of a voltage ELCB is simple. One terminal of the relay coil is connected to the metal body of the equipment to be protected, while the other terminal is connected directly to the earth. If there is any insulation failure or if the live phase wire comes into contact with the metal body, a voltage difference appears across the terminals of the coil.

When this voltage difference exceeds a predetermined limit, a current starts flowing through the relay coil. This current is sufficient to actuate the relay, which then trips Earth Leakage Circuit Breaker in the circuit and isolates the equipment from the supply.

It is important to note that a voltage ELCB can only detect and protect the specific equipment or installation to which it is attached. It cannot detect insulation leakage in other parts of the system.

Current ELCB or Residual Current Circuit Breaker (RCCB)

The working principle of a current ELCB, also known as a Residual Current Circuit Breaker (RCCB), is different from that of a voltage ELCB. While voltage ELCBs are often referred to as simple ELCBs, current ELCBs are commonly known as RCCBs or RCDs (Residual Current Devices).

In a current ELCB, a Current Transformer (CT) core is energized from both the phase and neutral wires. This core has two windings: one for the phase and neutral currents, and another for the relay coil.

Under normal operating conditions, where there is no current leakage, the phase and neutral currents are equal, resulting in a zero-ideal resultant magnetic field.

However, when an earth leakage happens, part of the phase current may start flowing through the leakage path to the earth instead of returning through the neutral wire.

As a result of this, the amount of the neutral current passing through the RCCB is not equal to the phase current passing through it.

When this difference in current exceeds a predetermined value, the current in the secondary winding of the CT core becomes sufficiently high to actuate the attached electromagnetic relay.

This relay then trips the circuit breaker, cutting off the power supply to the equipment under protection and safely isolating the electrical appliances.

Construction of ELCB


Now let's see the construction of ELCB to understand how they function. ELCB consists of various components that work together to ensure electrical safety. Here are the key components found in most ELCBs:

  • Relay Coil: The relay coil is an important part of an ELCB. It is responsible for detecting the voltage or current difference that indicates an insulation failure or earth leakage.
  • CT Core: The CT core is the heart of a current ELCB or RCCB. It consists of two windings: one for the phase and neutral currents and another for the relay coil. The currents passing through these windings create a magnetic field that is used to detect earth leakages.
  • Electromagnetic Relay: The electromagnetic relay is connected to the secondary winding of the CT core. When the current difference exceeds a certain threshold, the relay is actuated, triggering the circuit breaker to disconnect the power supply.
  • Circuit Breaker: The circuit breaker is responsible for the isolation of faulty equipment from the supply. When there is current leakage or insulation failure occurs. It breakers the supply of faulty circuits. And protect humans and equipment from shock hazards.
  • Terminal Connections: ELCBs have terminal connections for connecting the equipment or installation to be protected, the earth, and the power supply. These connections enable the ELCB to monitor the electrical circuit and respond to any faults.


ELCBs offer several advantages in electrical circuits, making them essential safety devices. Here are some of the key benefits of using ELCB:

  • Protection against Electric Shocks: The main function of ELCB in the circuit is to protect the individual who is come in contact with a live part by isolating faulty equipment from the power supply.
  • Detection of Insulation Failures: ELCBs continuously monitor current passing through a phase and returning from neutral. If insulation failure occurs this current will not equal in magnitude and this activate relay which trips ELCB followed by isolating the faulty circuit.
  • Enhanced Electrical System Safety: ELCBs contribute to overall electrical system safety by providing an additional layer of protection against electrical faults. They complement other safety devices, such as circuit breakers and fuses, to create a comprehensive safety network.
  • Reduced Risks of Fire and Electrical Accidents: By promptly detecting and interrupting circuits with insulation failures or earth leakages, ELCBs help reduce the risks of fire and electrical accidents. Their ability to quickly respond to faults minimizes the potential for damage and harm.
  • Ease of Installation and Maintenance: ELCBs installation is simple they can be mounted on din rail. And maintenance of them is easy we just need to press the test button to check the healthiness of ELCB. Also, we can check the sensitivity of ELCB by using elcb tester for reliable operation.

FAQ Related to ELCB

What full form of ELCB?

ELCB stands for Earth Leakage Circuit Breaker.

Why 30mA ELCB is used for domestic application?

Generally for domestic and industrial applications where human intervation happen frequently, 30mA ELCB is used. Because beyond 30mA leakage current become dangerous and can be fatal.

What is the purpose of an ELCB?

The purpose of ELCB in Electrical circuits is to protect personnel against electrical shock.
And detect insulation failure in the circuit

How does an ELCB work?

The working of ELCB is based on the monitoring current flowing through phase and neutral. If the difference is observed between the current flowing through the line and the return from the load via neutral then elcb operates and isolates equipment from the supply

What is the difference between an ELCB and an RCCB?

RCCB stands for Residual Current Circuit Breaker. While both ELCBs and RCCBs are designed to protect against electrical shocks, they operate differently. An ELCB detects leakage currents between the live wire and the ground, while an RCCB detects any imbalance in the current between the live and neutral wires. RCCBs are more commonly used in modern installations as they provide enhanced protection.

Where are ELCBs typically used?

ELCBs are commonly used in residential, commercial, and industrial electrical installations to protect against electrical shocks. They are often installed in electrical distribution panels or consumer units to safeguard circuits and appliances.

Can ELCBs protect against all electrical faults?

No, it only protects against earth leakage currents. They are not designed to protect against overloads or short circuits. To protect against overload and short circuits MCB must be used along with it in electrical installations

How to test an ELCB?

It can be tested using an ELCB tester. These testers simulate a leakage current and measure the response time of the ELCB. It is recommended to have tested periodically.

In conclusion, ELCBs play a vital role in ensuring electrical safety by detecting insulation failures and earth leakages. These devices, whether voltage or current ELCBs (RCCBs), protect against electric shocks and minimize the risks of fire and electrical accidents. By understanding the working principle and construction of ELCBs, we can appreciate their significance in safeguarding electrical installations and the people using them.

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