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.
Miniature circuit breaker (MCB) is an automatically operated electrical switch is used to interrupt the circuit under fault conditions such as overload and short circuit.
It was invented by Mr. Stotz-Kontakt in 1891.
MCB does not interrupt the circuit under the earth fault condition.
CONSTRUCTION
There are basically four types of MCB,s such as:-
1. Single-pole MCB 2. Two-pole MCB
3. Three-pole MCB 4. Four-pole MCB
Actuator knob:
It involves turning on and off operation of the MCB. This is the only mechanism used to indicate the status of the miniature circuit breaker. If the knob is in the upward direction, it is considered as ON position, if it is in a downward position,it is considered as off position.
Solenoid/magnetic trip coil:
It is a coil used to trip the circuit breaker under short circuit and instantaneous fault condition. It is connected in series with the inIput line.The inner part of the coil consists of a tripping rod, plunger, and a return spring.
Bimetallic strip:
A bimetallic strip is a small connecting metal that is associated with the tripping mechanism. It is a combination of steel and copper or steel and brass. Mostly steel is used since the resistivity of the steel is high.
The bimetallic arrangement is used to trip the circuit under an overload condition. It works based on “the physical state of the metal changes when the temperature of increase”.
Arc chute:
Arc chute is a bunch of steel plates with zinc-coated material arranged. The main purpose of the arc chute is quenching the arc which developed inside of the MCB while breaking the circuit.
Connection screw:
An electrolytic copper or steel screw allows us to connect the MCB to the power source. Mostly the bottom and top side screw indicate the output and input terminal.
Copper braid:
It is used to connect the moving element to the standstill element.
DIN rail connector:
The DIN rail connection is used to mount an MCB in a rack.
Encloser:
All the operations are performed inside of the encloser and which is riveted to get better mechanical strength. The encloser is made up of high insulated fiberglass.
WORKING
The circuit breaker mainly operates during short circuits and overloads.
The overhead protection is achieved by a bimetallic stripwhen the overload occurs the bimetallic strip becomes heat and starts to deflect or bend. In doing so, it releases the latch mechanism and causes the contact to open.
Whereas, the short circuit protection is given by the solenoid coil. On the occurrence of a short circuit, the short circuit current energizes the solenoid coil, thus the coil operates the plunger to move and to strike the trip lever which causes an immediate release of the latch mechanism.
The operating time of a miniature circuit breaker is less than 5 milliseconds. The miniature circuit breakers are available with different ratings such as 5, 6, 10, 16, 20, 25, etc.
The arc chutes are used to vanish the arc produced in the circuit breaker while interrupting the circuit.
Types of MCB on the basis of Tripping Characteristics
The tripping current and operating time of each MCB types are given in the table below.
