Dismantling MCCB, ELCB, and RCCB and Identifying Various Parts

The MCCB (Molded Case Circuit Breaker), ELCB (Earth Leakage Circuit Breaker), and RCCB (Residual Current Circuit Breaker) are essential protective devices used in electrical systems to safeguard the circuit from over currents, earth leakage, and residual current. Dismantling these devices will allow you to identify their internal components, understand their working principles, and how they contribute to safety in electrical installations.

Here is the process for dismantling and identifying the components of each device:

1. Dismantling and Identifying Components of an MCCB (Molded Case Circuit Breaker)

MCCBs are used to protect electrical circuits from overcurrent and short circuits. They are commonly used in industrial and commercial applications.

Procedure to Dismantle MCCB:

  1. Power Off the MCCB:

    • Before dismantling the MCCB, ensure the power supply is switched off to avoid electrical shock hazards.

  2. Remove the MCCB from the panel:

    • Unscrew the mounting screws of the MCCB from its housing or panel and gently pull it out.

  3. Open the MCCB Housing:

    • Use a screwdriver to remove the screws from the casing of the MCCB. Once the screws are removed, open the front panel or casing.

  4. Identify the Internal Components:

    • Operating Mechanism:

      • Handle/Lever: The handle or lever is used for turning the MCCB on or off.
      • Spring Mechanism: A spring mechanism provides the energy to trip the breaker during overcurrent or short-circuit conditions.

    • Contacts:

      • Main Contacts: The primary contacts that open and close to allow or interrupt current flow.
      • Arcing Contacts: Contacts that are designed to absorb the heat generated when the main contacts open and prevent arcing damage.

    • Trip Unit:

      • The trip unit is the brain of the MCCB and contains overload and short-circuit protection.
      • Thermal Trip Mechanism: This is a bimetallic strip that bends when the current exceeds the rated value, causing the breaker to trip after a delay.
      • Magnetic Trip Mechanism: This is a solenoid that activates instantly to trip the breaker during a short circuit by sensing an extremely high current.

    • Arc Extinguishing Chamber:

      • The arc extinguishing chamber contains elements that help cool the arc and prevent it from sustaining, thus improving the MCCB’s ability to interrupt high currents.

    • Terminal Blocks:

      • These are the points where the input and output wires connect to the MCCB.

    • Shunt Release and Under-voltage Release (Optional):

      • Shunt Release: Automatically trips the breaker when the current exceeds a preset value.
      • Under-voltage Release: Trips the breaker if the voltage falls below a certain threshold.

2. Dismantling and Identifying Components of an ELCB (Earth Leakage Circuit Breaker)

ELCBs are safety devices used to detect and disconnect the circuit when a leakage current flows to the ground, preventing electrical shock hazards.

Procedure to Dismantle ELCB:

  1. Power Off the ELCB:

    • Ensure the power supply to the ELCB is turned off before dismantling to prevent electrical accidents.

  2. Remove the ELCB from the panel:

    • Unscrew the mounting screws and disconnect any incoming and outgoing wires from the terminals.

  3. Open the ELCB Casing:

    • Use a screwdriver to remove the screws securing the casing. Open the housing to access the internal components.

  4. Identify the Internal Components:

    • Earth Leakage Sensing Coil (Current Transformer):

      • The core component of the ELCB is a current transformer (CT) or sensing coil. It detects the leakage current by monitoring the difference between the live and neutral wires.
      • If any imbalance is detected (i.e., leakage to earth), the CT will trigger the tripping mechanism.

    • Trip Mechanism:

      • The trip mechanism is responsible for opening the contacts and disconnecting the circuit when a leakage current is detected.
      • The mechanism may include a bi-metallic strip or a magnetic release system, depending on the design.

    • Contacts:

      • Main Contacts: These are the contacts that open and close to control the flow of current.
      • Auxiliary Contacts: These provide additional functions, such as signaling.

    • Test Button:

      • The test button allows you to simulate leakage conditions and test whether the ELCB is functioning properly. Pressing it will trip the device if it is working.

    • Terminal Blocks:

      • These are where the incoming and outgoing connections are made, such as the supply lines and load wires.

3. Dismantling and Identifying Components of an RCCB (Residual Current Circuit Breaker)

RCCBs are devices that detect residual current (current leakage to earth) and disconnect the circuit to protect against electric shocks, ensuring personal and equipment safety.

Procedure to Dismantle RCCB:

  1. Power Off the RCCB:

    • Before dismantling, ensure the circuit is de-energized by turning off the power supply.

  2. Remove the RCCB from the panel:

    • Unscrew the RCCB from the panel or mounting base, and disconnect all wires.

  3. Open the RCCB Casing:

    • Unscrew the casing screws and open the housing to reveal the internal components.

  4. Identify the Internal Components:

    • Residual Current Sensing Core (Current Transformer or Differential Transformer):

      • The core component of an RCCB is the differential transformer or current transformer that detects any imbalance between the live and neutral currents. If leakage current occurs, the transformer generates a differential signal to trip the breaker.

    • Trip Mechanism:

      • The trip coil or solenoid is activated when a differential current is sensed, and it operates a spring-loaded mechanism to trip the breaker.
      • The mechanism typically uses magnetic or mechanical release to quickly open the contacts in the event of a fault.

    • Contacts:

      • Main Contacts: These contacts open and close based on the trip mechanism.
      • Auxiliary Contacts: Provide auxiliary functions such as remote signaling or indicating when the breaker has tripped.

    • Test Button:

      • The test button allows you to simulate earth leakage conditions and check if the RCCB trips correctly, ensuring it is in proper working condition.

    • Terminal Blocks:

      • The incoming and outgoing terminals are where the supply and load wires are connected to the RCCB.

Comparison of Components in MCCB, ELCB, and RCCB

Component MCCB ELCB RCCB
Main Contacts Yes, for normal operation Yes, for switching circuit Yes, for switching circuit
Trip Mechanism Thermal (overload) + Magnetic (short-circuit) Earth leakage detection coil + mechanical release Residual current detection core + mechanical release
Earth Leakage Detection Not applicable Yes, detects leakage current Yes, detects residual current imbalance
Test Button No Yes, for testing earth leakage Yes, for testing earth leakage
Arc Extinguishing Mechanism Yes, to manage high fault currents No No
Auxiliary Contacts Yes, depending on the model Yes, for auxiliary functions Yes, for auxiliary functions
Overload Protection Yes No No

Conclusion:

Dismantling the MCCB, ELCB, and RCCB allows us to understand their internal components and how they function to provide protection in electrical systems. The MCCB is designed for overcurrent and short-circuit protection, the ELCB detects leakage currents to earth, and the RCCB focuses on detecting residual current imbalances. Identifying these parts helps in understanding the operational mechanisms of each device and how they protect electrical circuits from faults and hazards.