What is RCCB used for and what causes RCCB to trip?

The RCCB is the proper device to detect and trip against electrical leakage currents. This device is used to protect the equipment and people from low-level ground faults. This device uses the residual current sensing method to detect ground faults. The RCCB will operate if there is a difference in current between any two phases, the differential current is called residual current. If this device detects any faults then it would prevent the accidents by disconnecting the main circuits. The operation of this device is based on Kirchhoff’s current law, it states that the incoming current in a circuit will be equal to the outgoing current from that circuit. Mostly the RCCB is generally used in series with an MCB. The phase and neutral wires are connected through an RCCB, and these devices are widely used for protection from leakage current of 30, 100, & 300ma.

When will RCCB trip

A Residual current circuit breaker can provide protection against electrocution or electric fires and it does this by cutting off the current flow automatically when it senses a leakage current from a circuit.

How RCCB work

The RCCB consists of a core balanced transformer, the line and neutral conductors are connected to the transformer in the RCCB, so if the line current and neutral current is the same and opposite then the core will stay balanced. So during the case in which the neutral current is different from the line current then the transformer would generate output and this output will trip the RCCB and so the circuit will break.

What are the types of residual current circuit breakers?

The RCCB is classified into two types one for single-phase and the other for three-phase. The two-pole RCCB is for single-phase and it has a live wire and a neutral wire slot in it. The four pole RCCB is used for three-phase and it would have four slots in which we can connect the three-phase wire and the neutral wires.

What are the characteristics of RCCB?

  • Phase and neutral wires are connected through RCD
  • The circuit will be tripped if there is an earth fault current
  • The amount of current that flows through the phase, should return through neutral
  • It detects by RCD, if there is any mismatch between the current flows through the phase and neutral then it would trip very fast

What is the difference between ELCB and RCCB?

  • RCCB will only have a line and neutral connection
  • The purpose of these devices are the same but their working is different
  • RCCB stands for residual current circuit breaker whereas ELCB stands for earth leakage circuit breaker
  • RCCB is not connected with earth wire, whereas ELCB’s working is related to the earth leakage current
  • RCCB can detect any earth fault
  • The ELCB would need a sound earth connection, as does the equipment it protects
  • RCCB doesn’t have an earth connection, but it can detect current flow to earth

What are the advantages of RCCB?

  • It does not trip falsely
  • It is not affected by lightning strikes
  • In case if there is no connection between the ground and enclosure of the device, and if anyone touches the metallic body of the device. So in this case, the incoming and the outgoing current will be different and the RCB will trip in contrast with the ELCB

What are the disadvantages of RCCB?

  • It won’t protect against overheating
  • It won’t protect against live neutral shocks, it is because the current in the neutral and live is balanced.
  • If the socket outlet in RCCB is wired in the wrong way with its line and neutral terminal then it won’t operate.
  • It won’t protect against the current overloads
  • The RCCB’s are mostly designed to operate normal waveforms, so if the loads create a non-standard waveform then the RCCB won’t operate

What is the specification of RCCB?

The RCCB has the following specification

  • Sensitivity in milli-Amperes
  •  Current rating in amperes
  • Short circuit rating in kilo amperes
  • Poles – 2 poles or 4 poles
  • Shock and vibration resistant


post-graduate in Electronics & communication.

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