13 January 2018

ELCB OR Working of ELCB OR Residual Circuit Breaker ( RCB )

Principle of ELCB

  • The working principle of ELCB is based on core balance or differential current protection. 
  • When there is no leakage or fault in the system, the current passes through phase and neutral is same.
        IP = IN
  • When there is fault, the current flows through load to earth.
         IP = IN + IL
  • The phase and neutral conductor passes through core and net flux becomes zero under balance condition. 
  • If there is an earth fault, the induced emf in the secondary due to difference in the flux or current between incoming path and outgoing path. 
  • The terminal of secondary winding is connected to relay which open main contact due to tripping mechanism. 
  • The wiring of single phase / three phase ELCB is done such that all phase and neutral connection done in the ELCB otherwise due to switching of load, the circuit breaker trip. 
  • The circuit breaker of neutral conductor of the load side is not connected to earth. If it is connected to earth, the ELCB trips continuous. 
  • If the ELCB shows continuous trip, there should be fault in neutral circuit. 
  • The current setting of the ELCB is done up to maximum 30 mA because any person’s body does not withstand more than 30 mA leakage current. 
  • There should be no guarantee for person’s life if current passes through body more than 30mA. 
  • This type of ELCB is current operated therefore it is called as residual circuit breaker ( RCB ).  
Voltage operated ELCB
  • The voltage operated earth leakage circuit breaker consists of

Contact switching system and
Voltage sensitive trip coil
  • The voltage sensitive trip coil is connected between metal frame of device to be protected and earth connection. 
  • If the voltage of the metal frame is protected above the relay coil setting, the ELCB will be operated.

Relay coil voltage
  • The relay coil will operate above 40 V rise when earth electrode resistance is 5000 ohm / 24 V for 2000 ohm. 
  • A test device / switch is given in order to check the operation of ELCB when voltage coil of trip coil exceed than predetermined level ( 40 V or 24 V )

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