What is Residual Current Circuit Breaker (RCCB) and its function?

What is Residual Current Circuit Breaker (RCCB) and its function?


Current leakage in an electric circuit leads to what?

A complete disaster, the least you would say, right?

So,there must be a device that has the capability to sense the leaking of the current and delink the circuit immediately.

RCCB serves this purpose. Residual Circuit Current Breaker (shortly known as RCCB) is an electric gadget that prevents any electric explosion or shocks by delinking the circuit when there is leakage of current into the earth wire. Along with that, it also protects against electric shocks due to direct contact.

The function of the device piqued your interest, agree?

Alright, let’s dig deep and know more about it.

RCCB and its Function

RCCB is a current sensing device that senses any current imbalance and trips the circuit instantly.

Do you ever happen to know about how current flows in an electrical circuit? To completely grasp the working principle of RCCB, let’s understand the rule that it follows. RCCB works on Kirchoff’s current law principle, stating that incoming current must be equal to outgoing current.

Incoming =Ioutgoing

RCCB, thus senses the deviation in current values between live and neutral wires. If there is a difference between the current in-flow and out-flow, then there is a chance of short-circuiting. In case of a fault, the current in the neutral wire gets reduced, which could be dangerous if not maintained properly. That difference between the two current values is known as residual current. When RCCB senses that difference (residual current), it immediately gets triggered to trip off the circuit and prevent any loss.

The next question that we would like to address is about RCCB’s sensitivity.

Sensitivity of RCCB

Before we understand the sensitivity level of RCCB, let us know about how the human body reacts when contacted by a live wire.

What level of electric shock can prove to be fatal for the human body?




Well, it has been proven that a human body is comfortable with an electric shock of 30mA.

Anything above that is guaranteed death. Nonetheless, an electric shock of 10mA onwards may lead to muscular contraction, and further increment would result in respiratory paralysis at around 30mA.

Hence, RCCBs are designed to sense even a small amount of residual current. The purpose is to prevent any electric leakage and the perils of a short circuit.

Classification of RCCB

RCCBs are classified based on their types and ratings.

Let’s shed light on the types of RCBBs.

AIt is sensitive to alternating current or pulsating direct current.  
BIt is used to detect residual sinusoidal current up to 1000 Hz and pulsating direct current.  
FIt protects the circuit using single-phase variable speed drivers.  
ACThis type is sensitive to sinusoidal residual currents.  

There are three types of RCCBs.

  • 2 Pole RCCB
  • 4 Pole RCCB
  • 3 Pole RCCB

Hold on, before we embark on learning the types of RCCBs, understanding Pole and Phases is mandatory.

The single-phase has one live and one neutral wire, while three phases, as its name suggests, have three live wires and a neutral.

2 Pole RCCB:

2 Pole RCCB is used in a single-phase connection with one live wire and one neutral phase. It has two ends where the live and neutral wires are connected. The body of 2 Pole RCCB is formed so that a Rotary switch is used to switch the RCCB back to OFF and ON positions. Along with that, there is a test button that is used to test its functionality.

4 Pole RCCB:

4 Pole RCCBs are used in a three-phase supply connection, where there are three live phases and a neutral wire. Here, it also serves as an additional connection for the supply’s neutral. Unlike 2 Pole RCCB, it has two ends where three phases and a neutral wire would be connected. However, it is similar in function and construction to 2 Pole RCCB.

3 Pole RCCB:

Comparable to a 4 Pole RCCB. It is used in a three-phase three-wire system. Apart from that, 3 Pole RCCB has the same function and construction principle as the other two RCCBs explained above.

RCCB ratings

As mentioned above, human beings can sustain an electric shock of up to a magnitude of 30mA. Therefore, RCCB in low voltage protection is used to prevent the perils of a short circuit. The rating values vary from 10 mA, 30 mA, 100 mA, 300 mA, and 500 mA to 1000 mA.

Are you wondering why there are different residual current sensitivity levels?

Well, different sensitivity levels have a purpose. As mentioned above, the ideal protection level is at 30 mA. However, if one can’t use 30 mA, 100 mA will serve the purpose but to a little extent.

Caution: A 300 mA device must not be used for shock protection; it is designed to protect from failure and fire protection.

Hence, RCCB is designed and developed to protect an electric circuit of any value. They prevent small electric shocks between 10 mA and 30 mA and high-value dangers such as equipment failure and fire at a current of up to 1000 mA.

Now is the time to disintegrate an RCCB and learn about its parts.

Internal Circuitry of RCCB

Here are the internal parts of an RCCB.

  1. Incoming and outgoing terminals
  2. Contact
  3. Reset button
  4. Sense circuitry
  5. Solenoid
  6. Test button
  7. Test wire
  8. Sense coil

As their names suggest, the incoming and outgoing supplies are connected at their respective terminals, and the earth connector is connected through supply to load. Upon pushing the reset button, it allows current to pass, and a solenoid is used to keep the circuit closed when the reset button is released.

In normal operation, all the current from live wire returns to neutral wire through a solenoid which serves as a differential current transformer surrounding the live and neutral conductor. However, in the case of a fault, the returning current adopts a different path resulting in an imbalanced current RCCB detection.

The device is designed and developed to detect any short circuit and interrupt the current in a fraction of a second so that the chances of electric shocks could be drastically reduced.

Applications of RCCB

Who can deny that an electric shock is terrible, especially when a person gets in contact with a live wire?

RCCB provides real-time protection against any short circuit, especially in big industries where high voltage commercial setups are devised. As we know that, there is always a risk of electric leakage and short circuit, which results in fatal electric shocks, the importance of RCCB in a circuit cannot be undermined, and it plays an essential role in keeping the circuit smooth.

Advantages of RCCB

  • It helps in preventing any major electric shock and electric current leakage
  • It operates automatically; when there is an imbalance in the incoming current and outgoing current, it will automatically trigger to trip off the circuit.
  • Protects voltage fluctuation-it comes with a filtering device that detects even a momentary change in the voltage level.
  • It comes with dual termination options for both cables and busbar connections
  • It has multiple sensitivity levels, which can be used depending upon the current value
  • Available for single-phase supply as well as three-phase supply connection.
  • Highly sensitive, it can detect even a minor change in the current value
  • It is more sensitive than ELCB and can detect a little current leakage

Limitations of RCCB

  • It doesn’t offer protection from live-neutral shock.
  • It is designed to operate only at normal supply standard waveform.
  • It doesn’t offer protection against current overloads.
  • It causes Nuisance Tripping. Sudden changes in the electric load can cause a small current to flow to the earth. Since RCCB is a highly sensitive device, it may trip the circuit.
  • RCCB doesn’t protect from the overheating that strikes in case of improperly screwed cable conductors or if they are not adequately tightened at terminals.

An RCCB price

The price of an RCCB varies depending upon the quality you choose to buy. Companies like Schneider offer a range of quality RCCB and that too at an affordable price. Hence, in today’s time, it has become relatively easy to get protection from electrical mishaps at a low cost. However, it is strongly recommended to get advice from a professional before buying an RCCB from anyone. Now you know the function, construction, and working principle of an RCCB, it is pretty easy for you to decide what level of RCCB is needed for your desired circuit.

Wrapping up

RCCBs are essential circuit devices that help in protection against any electrical mishap primarily caused by an earth fault. A well-set RCCB will offer thorough protection from any electric shock and ensure no fatal injury caused by any accidental touch or contract of a human being with a live war. If you want your circuit to be danger-free, RCCB is a must-have device. Install it in your circuit and stay safe and secure from the perils of any short circuit. The rapidly increasing short-circuiting makes RCCB an essential.


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