Question

What is forward and reverse bias?

Answer 1

### **Working Principle of ELCB (Earth Leakage Circuit Breaker)**

An **Earth Leakage Circuit Breaker (ELCB)** is a safety device used to prevent electric shocks and protect electrical installations from leakage currents. It works by detecting leakage current flowing to the earth and disconnecting the power supply if the leakage exceeds a certain threshold.

#### **Types of ELCB**
1. **Voltage Earth Leakage Circuit Breaker (Voltage ELCB)**
2. **Current Earth Leakage Circuit Breaker (Current ELCB) or RCCB (Residual Current Circuit Breaker)**

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### **Working Principle of Voltage ELCB**
- It is connected between the electrical installation’s earthing and the earth wire.
- When leakage occurs due to insulation failure or a fault in the system, a voltage appears between the earth and neutral.
- The ELCB senses this voltage difference and trips the circuit, disconnecting the power supply.
- However, this type is now outdated and replaced by RCCBs.

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### **Working Principle of Current ELCB (RCCB)**
- It works on the principle of **differential current sensing**.
- The live (phase) and neutral wires pass through a **core-balanced current transformer (CBCT)**.
- Under normal conditions, the current in the phase and neutral wires is equal, and the sum is zero.
- If there is any leakage (such as through a person or faulty insulation), the returning current in the neutral wire is less than the phase wire.
- This imbalance creates a residual current, which is detected by the circuit.
- When the leakage exceeds a safe limit (typically **30mA for human safety** and **100mA+ for equipment safety**), the ELCB trips and disconnects the supply.

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### **Advantages of ELCB**
✅ Prevents electric shocks and fire hazards.  
✅ Quickly disconnects power in case of leakage.  
✅ Protects human lives and electrical equipment.  
✅ Works efficiently in residential, commercial, and industrial applications.  

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### **Limitations of Voltage ELCB**
❌ Does not detect small leakages effectively.  
❌ Needs a separate earthing connection to function.  
❌ Replaced by modern **RCCB** and **RCBO** devices.  

Would you like more details on RCCB and how it differs from MCB?