Residual Current Circuit Breaker

This device is important in electrical wiring installation.It is a life guard device to protect from electric shock.Others circuit breaker only can detect the fault from over current and short circuit but cannot detect the current leakage.

That why RCCB is very important.Only this device can detect the current leakage.The current leakage can cause the injury or dead for human and can lead to fire hazard.When design the distribution panel board,please make sure this device include in our planning to for consumer safety and avoid equipment from damage.

What is Residual current circuit breaker ( RCCB )?


The main purpose for RCCB is a provide protection against direct and indirect contact of personnel or livestock and probable  fire.Prevents shocks caused by earth leakage which could be fatal.

Principle of operation

How RCCB can detect the current leakage? use the simple theory of  balance current through the current transformer.The residual current device monitor the different between the load flowing through the current transformer and ensure the value of ampere is approximately zero.

If current leakage happen,the current flow will not in zero value,the different value exceed the rccb current rating,it can make the current transformer energized and send the signal to the plunger to cut off the breaker.The important thing to ensure this device operate properly,the earthing cable must be installed in electrical wiring.If not,RCCB cannot detect the current leakage cause the current is floating in circuit.

Protection against electric shock

1) protection in the case of indirect touch (indirect protection of persons) and fault protection when disconnecting impermissible high touch voltages caused by short-circuit to exposed conductive parts.

2) protection in the case of direct touch (direct protection of persons) – disconnection as additional protection where live conductors are touched directly.Hazardous shock currents are disconnected within no time if the rated residual current of the device is In – 30 mA.

3)  protection against electrically ignited fire (fire protection) – if the rated residual current of the device is In – 300 mA

General Description Of RCCB

  • To open a circuit automatically in the event of an earth leakage between phase and earth and/or neutral and earth. With effective protection against human contact to earth points.
  • Protection against Direct Contact of persons or livestock with live part.
  • Protection against Indirect Contact of persons or livestock with exposed conductive parts which have become live under fault conditions.
  • Protection against Electrical Fires caused by high resistance fault arching but not causing the over current protection device to operate.
  • Designed with surge current withstand capability to prevent nuisance tripping during thunderstorms. Conditionally surge current proof (250A, 8/20us), without time delayed tripping.
  • These devices are sometimes called an ELCB or RCD.
  • Use in domestic, commercial and industrial installations.

RCCB Sensitivity

1) 30mA ( mili ampere )

  • Tripping current designed for additional protection against direct contact, or where specially required by wiring regulations, the 30 mA RCCB protects against leakage currents and indirect contact with earth loop impedance up to 1667 Ohms; for use as additional protection against direct contact, residual tripping current must not exceed 30 mA.

2) 100mA ( mili ampere )

  • Tripping current is suitable for protection against indirect contact and leakage currents for larger installations; the 100 mA RCCB’s operate within 30 ms, but do not provide the same level of personal protection as the 30 mA units; the 100 mA RCCB protects against leakage currents and indirect contact with earth loop impedance up to 500 ohms.

3) 300mA ( mili ampere )

  • A less sensitive protection suitable for large installations having high levels of leakage current; 300 mA RCCB’s protect against leakage current and indirect contact up to 167 ohms earth loop impedance.

RCCB possible application area

1) For universal use in normal circuits

2) For additional protection of socket outlet circuits

3) To achieve a high degree of service security

4) For commercial and industrial power installations

RCCB wiring technique



  1. Hassan tayo says

    i love all the write up on some topics,it really interesting to discover some stuff that will never comes up during lectures hours in school.Thanks.

  2. hi i am electrician can i use rccb for home i need more about the rccb using function thank you

  3. Philip Oakley CEng MIET says

    The circuit equation isn’t quite right given the indicated current directions on the diagram. I1 and I2 are the same positive in-phase value, so the first equation should then be dI = I1 – I2 = 0 (note that in this case it is a minus not plus).

    The same applies to the difference ‘fault’ current, with the sign of I3 depending on which way you want to indicate the in-phase fault current to be. This also confuses the that that the three currents ‘sum to zero’ (Kirchoffs law) with the fault residual Id = I3.

    We actually have I1 (from Live 1) must equal = I2 (returned via Neutral wiring) + I3 (fault current returned separately via the case’s protective conductor aka ‘earth’).

    Finally, in a real three phase RCCB the torroid would include all three live conductors and the neutral (which if balanced has ~0 surrent) so it would be (L1+L2+L3 – N) = dI (currents summed at any instant relative to the reference phase).

    In all cases the torroid detects the current that did not return though the properly desired conductors (which all go through it), but rather returned through some stray fault wiring, or the protective ‘earth’ conductor.

    [In modern wiring systems we want the fault currents to go through our properly designed protective conductors because we know it will carry the fault current and trip the circuits without excess voltage, rather than having to hope that soil clay sand and dirt (‘earth’) might just cope ;-) ]

    • HI Morris,
      Thanks for the great input and detail explanation about RCCB.Hope with this we can more understanding about basic operation of RCCB

  4. Is Concrete batching plant and crusher plants are required RCCB?
    If, no ( not required ) means what type of prevention wants to take earth leakage / electrical shock ??
    If is required means what type of RCCB ( rated capasity ) wants to provide???
    How can i secure my workers from electrical shock ??

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