Today, electricity has become an absolute necessity in our life. But things were not as smooth as they are in present days. There was a time when electricity was used despite serious limitations. Frequent deaths due to electrocution especially in monsoons or in the bathroom due to faulty wiring or overflowing of electric current was very common in the past. And so was the outbreak of fire due to short-circuits and faulty current conditions.
With the passage of time, we have been successful in creating equipment & devices that not only detect faults and leakages in the electric current but has the ability to shut down the entire power supply.
Earth Leakage & Electric Shock:
Different kinds of faults exist in our electrical system, earth leakage is one of those faults. Whenever the current starts getting leaked from the conductor the situation is known as earth leakage/current leakage. We use multiple electronic appliances or equipment at our homes and offices such as PC, Laptop, Printers, and Machines that cause harmonic distortion to the current they consume. Also due to various other reasons such as insulation rupturing, weak insulation etc. The current leakage can be there. Due to the rupturing or weakening of insulation of the conductor, the current starts leaking and finds its way towards the ground since earth is at zero potential.
Now, to travel to ground the current needs a conductor or we can say a travel medium is required. Generally the ‘earth wire’ or the ‘Earth Conductor’ helps the current to travel to the ground but in case of current leakage if a human body comes in contact with the leakage current, it treats the human body as the conductor and through it, makes the way towards the ground. Due to this, the human body experiences a strong vibration known as ‘electric shock’.
As per the above chart, it is clear that we need to be very much cautious from the leakage current as it may prove lethal to us.
Protection from Earth Leakage:
In order to achieve protection from earth leakage, 2 kinds of protection devices are used, based on 2 different concepts:
- Voltage sensing ELCBs
- Current sensing RCCBs
- Voltage Sensing based Earth Leakage Circuit Breaker:
ELCB or Earth Leakage Circuit Breaker works on the principle of Voltage Sensing. ELCB is connected to the system such that one terminal is connected to the equipment for which the protection is required & the other terminal is connected to the earth. The voltage is measured between these 2 terminals which are observed as ‘0’ in an ideal case. However, in case of earth leakage, a voltage difference is created between these 2 terminals energizing the coil in the circuit breaker which in response trips the ELCB in case of earth leakage.
Disadvantages of an ELCB:
- Continuity of Earth is a must for ELCB to operate.
- For separate devices separate earthing shall be required otherwise the ELCB would not be able to sense the leakage.
- Diversion of protection can be there in case a proper earthing arrangement is not maintained by the user with ELCB.
- Mandatory wiring arrangement of the earth conductor from equipment to ELCB for its operation.
- Current sensing based Residual Current Circuit Breaker (RCCB):
What is an RCCB? ‘Residual Current Circuit Breaker’ or ‘RCCB’ is a current sensing based protection device which offers protection against earth leakage. RCCB works on ‘Kirchhoff’s Current Law’ which states that ‘The amount of current entering the circuit must be equal to the amount of current leaving the circuit’ i.e. the sum of the total (incoming + outgoing) current should be 0. To ensure this, inside RCCB there is a CBCT (Core Balance Current Transformer) which senses the magnitude of current entering the circuit & leaving the circuit. Whenever a current leakage is sensed, the relay associated with CBCT gets energized and trips the RCCB.
Advantages of RCCB
- Trips the circuit breaker even if the Earth continuity is not available.
- Accurate
- No individual earthing of devices is required
- Simplified wiring
RCCB inside Distribution Board:
RCCBs are connected parallel to the MCBs inside distribution boards. The neutral connection is done to the neutral links & phase is connected in parallel with MCB as the MCB offers protection against overload and short circuit, and RCCB offers the protection against earth leakage. The neutral is required for the RCCB in order to sense the incoming and outgoing current.
A special kind of distribution board called PPI ‘Per Phase Isolation’ Distribution Board is there in which there is a provision to install RCCB in each phase with separate neutral links provided for each phase such that, the phase which is experiencing a current leakage only that RCCB should trip and other phases can continue to work without any disturbance.
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Credit- C&S Electric. Published by Department of EEE, ADBU: tinyurl.com/eee-adbu
