CIRCUIT BREAKER

              Residual Current Circuit Breaker

RCCB is used to protect the electrical circuit from earth fault. Formally It is called as ELCB (Earth leakage Circuit Breaker). Sometimes it is also called as RCD (Residual current Device).
RCCB is named as Residual current circuit breaker because of it protects against residual current. Residual current means flow of leakage current between live conductor to earth. 
RCCB is specially designed to protect the electrical circuit against earth fault and human from electrical shock.
Construction
   

Construction

Main Parts of RCCB

Relay operating coil:
Pickup value of the relay coil is depending upon the leakage current rating of the RCCB. The current flow cannot be changed. 

Incoming/Outgoing Terminal:
Incoming outgoing terminal are used to connect the Load and source. Here source terminal should be connected on the top side and load terminal should connect on the bottom terminal.

Trip mechanism:
Trip mechanism is used to trip the circuit during fault condition.

ON/OFF switch:
The handle is used to switching on/off the RCCB.

Test Circuit: 
A Test switch is used to check the working condition of RCCB. A switch is connected between line to earth (in series with a resistor). When you press a switch the current starts flow from line to earth. Then RCCB trip the circuit as shown in following figure.

                                     

Working

                              

1.Under Normal condition

          The Total current flows in the phase wire is equal to neutral wire.

 i.e consider 10 Amps current is in  phase side and same current 10 Amps flows return in the neutral side also. Since the CBCT (core balance current transformer) do not sense any current when  IL=IN.

2.Under earth fault condition

         The fault current or leakage current (IE) starts flow from the phase wire (red) to earth wire (green) i.e consider leakage current is 300 mA. Since CBCT reads the unbalance current of 300 mA when the same current will be sent to the relay operating coil. if the leakage current exceeds the rated tripping level IΔn, then the RCCB trip the electric circuit.

Types

Three different type RCCBs are classified according to types of source used.
Type AC: Only AC source can be used.
Type A  : AC source + Pulsating DC source can be used.
Type B  : AC as well as DC can be used.

                          

Advantage of RCCB:

• It is used to protect against earth fault as well as Electrical shock
• The Main purpose RCCB is to protect the human from residual current.

Disadvantage of RCCB:

• RCCB do not have short circuit protection
• RCCB don’t offer protection against current overloads.
• RCCB will not protect against live-neutral shocks, because the current in the live and neutral is balanced. 
• RCCB is higher cost.