An RCCB (Residual Current Circuit Breaker) works by constantly monitoring the current flowing through the live (or phase) wire and comparing it to the current returning through the neutral wire. It trips when there's a significant difference between these currents, indicating a leakage current, thus protecting against electric shock.
Here's a breakdown of the process:
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Kirchhoff's Current Law: The RCCB's operation is based on Kirchhoff's Current Law, which states that the algebraic sum of currents entering a node (or a circuit) is equal to the algebraic sum of currents leaving the node (or circuit). In simpler terms, what goes in must come out.
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Current Monitoring: The RCCB continuously monitors the current flowing through the live and neutral wires using a sensing coil (also known as a differential current transformer). These wires are wound around a toroidal core.
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Normal Operation: Under normal operating conditions, the current flowing through the live wire is equal to the current returning through the neutral wire. The magnetic fields created by these currents in the toroidal core are equal and opposite, effectively canceling each other out. Therefore, no current flows in the sensing coil connected to the toroidal core.
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Fault Condition (Leakage Current): If a fault occurs, such as someone touching a live wire, a portion of the current will leak to earth (ground) instead of returning through the neutral wire. This creates an imbalance between the current in the live and neutral wires.
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Detecting the Imbalance: This difference in current creates a net magnetic field in the toroidal core, which induces a current in the sensing coil.
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Tripping Mechanism: The current induced in the sensing coil is fed to a highly sensitive tripping mechanism. When this current exceeds a pre-set threshold (typically 30mA for shock protection), the tripping mechanism is activated.
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Circuit Interruption: The tripping mechanism rapidly opens the contacts of the RCCB, disconnecting the power supply to the circuit and preventing electric shock. This happens very quickly, usually within milliseconds.
In essence, the RCCB acts as a safety device that detects even small imbalances in current, protecting people from potentially lethal electric shocks. It's important to note that RCCBs do not protect against overloads or short circuits. These are handled by MCBs (Miniature Circuit Breakers) or fuses. A typical residential electrical system often uses both an RCCB for earth leakage protection and MCBs for overload and short circuit protection.
