If one of us were to inadvertently touch the metallic body while it was still alive, how would we be protected?
Think about an Induction motor as an illustration. The motor’s frame is visible connected to the ground. So, there is zero risk of getting a shock if we touch the metal casing.
What does it mean, exactly, when we talk about leakage current?
As shown in the schematic below, if a person standing on Earth touches the LIVE point, their body acts like a resistance RL that appears between the LIVE and EARTH nodes.
When a person is grounded improperly, a current known as leakage current IL will flow between their body and the ground conductor. Fault or leakage current is the name given to this type of current.
Essential protection against these currents is provided by a tool known as an Earth Leakage Circuit Breaker.
Let’s talk about how the ELCB works both when everything is normal and when something goes wrong.
ELCB protection of three-phase systems
If you have a 3-phase ac supply, you can apply the same basic idea. The CT core receives all three lines in order to look for disproportions caused by leakage faults.
Currents are balanced and CT output is small under normal operating conditions. A non-zero output is generated by the CT when the fault condition is present, energizing the relay and tripping the circuit breaker because of the unbalanced currents.
Circuit breaker for earth leakage how it works
When nothing is wrong, that’s the norm. There is no current leaking, IL=0. That’s why in the diagram below, I1 and I2 represent equal and opposite currents. Since I1 and I2 produce fluxes that are equal and opposite in the current transformer core, these fluxes will cancel one another out.
When this happens, the circuit breaker won’t trip and the relay won’t be energized. Nothing has changed in the circuit, and it still functions normally.
An ELCB in action during a fault
Like we discussed before, when a fault occurs, a leakage current IL flows through the ground wire.
As a result, the I1 and I2 currents won’t balance out. Therefore, the current transformer core will be set up with a non-zero flux.
Connected Devices’ output will provide power to the relay coil. An electrical circuit breaker can be switched off by means of a tripping signal generated by the relay.
The user is safeguarded by the circuit breaker which trips when activated. ELCB has a response time of roughly 25msec.