- 1 What is a Residual Circuit Current Breaker (RCBB)?
- 1.1 What is the function and additional function of RCCB?
- 1.2 Working Principle of RCCB
- 1.3 Types and Ratings
- 1.4 Pole types of RCCB: The 2 Poles, The 3 Poles and the 4 Poles.
- 1.5 ABB
- 1.6 Schneider Electric
- 1.7 ABB
- 1.8 Schneider Electric
- 1.9 Ratings of RCCB
- 1.10 Understanding Tripping Curves
- 1.11 Limitations of RCCB
What is a Residual Circuit Current Breaker (RCBB)?
RCD, Residual-Current Device or RCCB, Residual Circuit Current Breaker. It is an electrical wiring device whose function is to disconnect the circuit when it detects currents leaking to the earth wire. It also gives protection against electric shock or electrocution caused by direct contact.
What is the function and additional function of RCCB?
Residual Circuit Current Breaker, RCCB
It is a device that has a mechanical switch attached with a residual tripping feature attached to it. As mentioned above, it will only break the circuit when there is a leakage current flowing to the earth or also known as earth fault. This is to minimize the risk of human life.
RCCBs usually can handle a fault or residual current of 1kA on their own if it is a fault to earth.
Wiring rules states that other devices should be operating together with RCCBs to provide protection. This can help improve the short circuit rating of RCCBs, thus for example a 1kA rated RCCB is able to operate at a fault level higher than 1kA.
*A Fault refers to an abnormal electric current. E.g a short circuit is a fault in which current exceed the normal load. It can also be refer to Residual current.
Residual Circuit Current Breaker with Overload protection, RCBO
This device is RCCB with a MCB, Miniature Circuit Breaker built in to it, also known as RCBO. It mainly protects against earth fault, overloads and short circuit currents. It also has the similar purpose of protecting lives like the RCD.
*To learn more about MCB, click here
Earth Leakage Circuit Breaker, ELCB
This device has the same function as the residual current circuit breaker, RCCB but it is a voltage sensor device. They are suitable for three-phase circuits and high current loads. The residual current level and tripping delay is often adjustable, thus allowing selectivity among different circuit breakers. Regardless, ELCB is an old device and the RCCB has better advantages
Working Principle of RCCB
An ideal circuit is that currents flows through the circuit via the live wire should be the same as the returning current via the neutral wire.
However, when an earth fault happens, current enters the earth wire by accident such as accidental contact with open wire. As a result, the current returning through then neutral wire is reduced. The difference in current between the live and neutral wire is called residual current. RCCB is designed such way that it continuously senses the residual current or the difference in current values between the live and neutral wires. Therefore, unless the residual current does not surpass the limit, the RCCB will disconnect the circuit.
Types and Ratings
|AC||Sensitive to residual sinusoidal alternating current only|
|A||Sensitive to residual alternating current and/or pulsating direct current|
|B||Provide protection of alternating residual sinusoidal current up to 1000Hz, pulsating direct current and smooth direct residual currents.|
|F||Provide protection for circuit using single phased variable speed drivers could be used.|
Pole types of RCCB: The 2 Poles, The 3 Poles and the 4 Poles.
2 Poles RCCB – Used in case of a single-phase supply connection that has only a live and a neutral wire.
3 Pole RCCB – Similar to a 4 Pole RCCB but it only has three wires of a three-phase system.
4 Pole RCCB – Used in case of a three-phase supply connection and also an additional connection for the neutral of the supply
Ratings of RCCB
- Residual Current Sensitivity – 10mA, 30mA, 100mA, 300mA, 500mA, 1000mA
- Different Residual Current Sensitivity Tripping level serves a purpose.
- The recommended tripping level for maximum shock protection is 30mA just like the Schneider Acti9 RCCB (Picture above).
- A tripping level of 100 mA will still give a degree of shock protection if it’s not possible to use a 30mA device.
- While a 300mA should never be used for shock protection, its purpose is to provide fire and equipment protection.
Understanding Tripping Curves
- If you are looking to buy RCBOs, you will notice that the type of tripping curves is displayed. This is because as mentioned earlier RCBOs has a MCB built in it. Therefore, we will be going through the 4 tripping curves that are available in our website Electgo.
- Tripping Curve B – MCB with Trip Curve B trips instantly at a rate of three to five times it’s rated current. They are suitable for cable protection, residential and light commercial uses.
- Tripping Curve C – MCB with Trip Curve C trips instantly at a rate of five to ten times its rated current. Typically used for high inductive loads. Suitable for domestic and residential applications.
- Tripping Curve D – MCB with Trip Curve D trips instantly at a rate of ten to twenty times its rate current. Used for extremely high inductive loads such as motor with high inrush current.
- Tripping Curve K – MCB with Trip Curve K trips instantly at a rate two to three times its rate current. It is very sensitive to short circuit. Suitable for highly sensitive devices such as semiconductor devices
Limitations of RCCB
- Only designed to operate on normal supply standard waveform
- They do not offer protection against current overloads: Current Overload refers to live-neutral fault; the RCCB won’t trip and may be damaged.
- Nuisance Tripping : Sudden changes in electrical load can cause a small, brief current flow to earth. Since RCCBs are sensitive and operate quickly; they may just disconnect.
- RCCB will not protect user from live-neutral shocks