20th September 2020

RCCB(Residual Current Circuit breaker)

What is Residual Current Circuit breaker(RCCB)

Failure of insulation in equipment causes current to flow through the insulation to the earth. Which is known as electrical leakage current. This current poses two severe risk factors which are:

  • Fire Risk
  • Electrocution(death caused by electric shock ) Risk

Physiological Effect of Electric Current on Human Body. Refer below Table

500 mAImmediate cardiac arrest, may result in death
70 mA – 100mACardiac fibrillation: the heart begins to vibrate and
no longer beats at a steady rate.
20 mA – 30mAMuscular contraction: Person remains stuck to the conductor.
1 mA – 10mAPrickling sensations

The Residual Current Circuit breakers(RCCBs) are the safest device to detect and trip against electrical leakage currents. Basically, it provides protection of people and equipment against any sort of electric shock caused by indirect contacts.


Working Principle of RCCB

In a healthy circuit, the sum of the current in phases is always equal to the current in the neutral and vector sum of all current is equal to zero. If there is any insulation fault in the current and leakage current flows to earth, in this situation currents are not balance and their vector sum is not equal to zero. This imbalance is detected core balanced current transformer(CBCT), the RCCB is tripped and supply to the load is interrupted.

Relevant Article: what is Core Balanced Current Transformer(CBCT).

Accidently a person can suddenly come in contact with an open live wire in an electrical circuit, due to insulation failure or any other reason. In that instance in the absence of RCCB, a ground fault may occur and a person will encounter electric shock. To overcome this sort of situations, Residual Current Circuit breakers(RCCBs) are the effective and safest device to detect and trip against electrical leakage currents.

Residual Current Circuit Breaker acts as isolation switching and also provides earth leakage protection. However these devices cant protect from short circuit, therefore RCCBs must be used in series with an MCB or fuse which protects RCCB from the potentially damaging thermal and dynamic stresses of any overcurrents. RCCBs are available up to 10kA withstanding capacity from short circuit.

Characteristics of RCCB

  • Phase and neutral are connected through RCCB
  • Automatically measures and disconnect the circuit when earth fault or leakage current occurs and which exceeds the rated sensitivity.
  • Also, fulfill the function of isolation in addition to earth leakage protection against earth fault/leakage current.
  • High short-circuit current withstand capacity – upto 10kA
  • Prevents from nuisance tripping due to transient voltage

Sensitivity of RCB:

sensitivity of RCB


Photo Credit : www.havells.com, https://cselectric.co.in

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