RCCB : Residual Current Circuit Breaker

 

A modern Earth Leakage Circuit Breaker (ELCB) is equipped with three transformers, consisting of two primary windings and an additional winding composed of various coils - phase coil, neutral coil, and wire-wound coil. When combined, these components create what is known as a Core Balance Current Transformer (CBCT).

In the balanced state, no current flows through the secondary winding of an ELCB. When an electrical fault occurs, current flows to the ground, disrupting the magnetic field's equilibrium. This disruption is detected by the phase and neutral wires, which transmit a signal to the sensing circuit through the secondary winding. Subsequently, the fault is identified, and the system triggers a signal to trip the current flow.

The main components of the RCCB (Residual Current Circuit Breaker) are: Three coils - one coil is connected in series with the phase, another coil is connected in series with the neutral, and the sensing coil is connected to the relay. The relay used in the RCCB is a current sensing relay, and its main function is to activate the circuit breaker contacts when a leakage current arises in the circuit.

The RCCB has a Test button connected in series with a current limiting resistor. When the button is pressed, the current flows through the coil connected with the neutral only, creating a direct path between the phase and neutral and resulting in a high current flow. The current limiting resistor restricts this high current to protect the circuit. The Test button is used to check if the RCCB is working correctly.

The number of turns in both coils connected in series with the phase and neutral are the same, ensuring that when an equal current flows in the circuit, they produce the same amount of magnetic flux. The coils are wound in opposite directions to each other.

RCCB Working Principle

The RCCB (Residual Current Circuit Breaker) operates on a straightforward principle. When the electrical circuit is functioning normally, the current flowing through the phase and neutral wires is equal. This creates balanced magnetic fields in the coils, which effectively cancel each other out. However, if there is an earth leakage or a fault in the system, the current becomes unbalanced, resulting in an unequal magnetic field. This imbalance induces a current in the sensing coil, which then triggers the relay to disconnect the power supply, ensuring safety.

RCCB Function

The main purpose of a Residual Current Circuit Breaker (RCCB) is to safeguard against leakage current faults. It cuts off the power supply when a leakage current fault, such as an earth leakage or electric shock, occurs. However, an RCCB cannot protect against short circuits or overloads. It can only detect leakage current, not high current flow or short circuits. Therefore, an MCB (Miniature Circuit Breaker) is always used alongside an RCCB. If a high current causes an imbalance in the circuit, the RCCB will trip. But if the current flow is balanced in both the incoming and outgoing lines, the RCCB will not trip, even if the current is high. For example, during a short circuit, a very high current flows, but it is balanced, so the RCCB cannot provide protection and may even get damaged due to the high current.

• Function: Detects imbalance between live and neutral currents.

• Operation: Trips the circuit if the difference between the current entering and leaving the system exceeds a set value (typically 30 mA for residential use), indicating a leakage current.

• Application: Commonly used in modern residential and commercial installations due to higher reliability and sensitivity.

• Monitoring: Continuously monitors the current flow through live and neutral wires.

• Tripping Mechanism: If there is a difference between the live and neutral currents (indicating a leakage to the ground), it trips the circuit. The imbalance suggests that some current is leaking out of the circuit (e.g., through a person to the ground).

Advantages of Current ELCBs

• The Current ELCB breaks supply to the complete circuit if power leaks from any part of the circuit.

• These are considered highly reliable when it comes to protection against electrical shocks.

• These have higher sensitivity and hence can detect minute anomalies and abnormalities.

• The current ELCBs have a consistent monitoring mechanism in place. This enables the device to break the electrical supply when the current threshold is exceeded.

• These do not require an earth connection.

Disadvantages of Current ELCBs

• If ELCBs are used with older appliances with a small leakage, then these may trip unnecessarily owing to their sensitivity.

• These are more expensive than voltage-based ELCBs.

• These ELCBs do not offer overload protection.

• These offer no protection against short circuits.

Overall, though, you will benefit more by investing in a current ELCB or RCCB instead of a voltage ELCB. This is because voltage-based ELCBs function on redundant technology that offers very limited protection as compared to RCCBs. While current-based ELCBs may be more expensive, these are a more reliable option when it comes to protecting your space from earth leakages and short circuits.