ELCB-Protection of Leakage Currents Using ELCB:

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ELCB- Earth Leakage Circuit Breaker:

How to protect ourselves if we accidentally touch a live metallic body?

For example, consider an Induction motor. If we observe, the body of the motor is connected to the earth. So if we touch the metal housing, there is absolutely no possibility of us receiving a shock.

Earthing of Induction Motor-ELCB
Induction Motor Earthing

Here, we will see what exactly the leakage current means.

If we standing on earth touch the LIVE point, then as shown in the circuit diagram below, our body is equivalent to a resistance RL appearing between the LIVE and EARTH points.

A current called leakage current IL will flow through the person’s body and the ground conductor. This current is known as a fault or leakage current.

The protection against such currents is essential and it is provided by the device called Earth Leakage Circuit Breaker.

ELCB-Earth Leakage Circuit Breaker
Earth Leakage Circuit Breaker

Let us discuss the operation of ELCB under normal and under fault conditions.

Operation of Earth Leakage Circuit Breaker:

ELCB working under Normal conditions:

The normal condition is when there is no fault. So the leakage current IL=0. Hence the currents I1 and I2 in the below figure will be equal and opposite. So the fluxes produced by I1 and I2 in the current transformer core will be equal and opposite and so cancel each other.

ELCB-Circuit Diagram
Circuit Diagram of ELCB

The relay will remain unenergised and the circuit breaker does not operate. The circuit continues to work without any problem.

ELCB working under the Fault conditions:

When the fault occurs, the leakage current IL starts flowing through the ground conductor as explained earlier.

Hence the currents I1 and I2 will not be equal to each other. So there will be a non-zero flux set up in the current transformer core.

The output of C.T. will energize the relay coil. The relay produces a tripping signal and applies it to the circuit breaker.

The circuit breaker operates, breaks the circuit, and protects the user. The reaction time of ELCB is about 25 ms.

Protection for three-phase circuits using ELCB:

The same principle can be extended if the ac supply is 3-phase-type. All the three-line are passed through the CT core to search for any imbalance due to leakage fault.

Under normal operating conditions, the currents are balanced and the output of CT is negligibly small. But under the fault condition, the currents are unbalanced, and a nonzero output is produced by the CT to energize the relay and trip the circuit breaker.

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