Managing Power Load: Importance of RCCB and Types of Residual Current Devices

Updated on July 5, 2021

Eventually, electricity is becoming a vital component of everybody’s lives, however, it comes with dangers to equipment and human life. Therefore, one cannot be careless when it comes to safeguarding equipment. Fire and electrocution are the two key risks related to electricity. 

RCCB (Residual Current Circuit Breaker) is a key safety measure when it comes to electrical circuits’ stability. RCCB is a current sensing device that can measure and disconnect automatically any circuit in a situation of a fault that occurs in a certain circuit or in case the current crosses the pre-set/rated sensitivity.  

An RCCB aids in protecting an individual from fatal electric shocks, besides fire and electrocutions. In addition, RCCBs are effective in case of an abrupt earth fault. The functioning of RCCB ensures that in cases like these, the electric circuit will swiftly trip, thus, safeguarding the person from an electric shock.  

RCCB operates on Kirchhoff’s law’s principle, which states that incoming current and outgoing current must be equal to each other. Therefore, an RCCB measures the underlying difference between the neutral and live wires. Ideally, the current that is flowing from the live wire to the circuit should equal the current flowing in the neutral wire. However, in case of any fault, the current flowing through the neutral wire is lowered, and the differential between the two would be referred to as residual current. And, after detection of a residual current, an RCCB is incorporated to trip off the circuit.  

The IEC 60755 standard broadly defines 4 types of Residual Current Devices for different AC applications. Each of these types of RCDs addresses different combinations, types, residual current waveforms etc.  

  • AC Type 

AC type of RCDs are normally used in cases wherein the fault current is expected to be at a similar frequency as the supply and sinusoidal. AC type RCDs are used for general purposes in a number of countries; for example, when a fault occurs in the supply conductors or maybe when the load is linear or resistive.  

  • A Type 

A few types of loads, like the ones having single-phase rectifying circuits, such as a heating plate, might create a pulsating residual current (DC). And, for such applications, A Type RCD would be required that can detect the type of residual current. These RCDs can even withstand a ‘smooth’ superimposed DC current up to 6 mA. Like AC type RCD, even A-type RCD can detect sinusoidal currents.  

  • F Type 

A few applications might have composite residual currents up to 1000 hz. For say, circuits with variable speed-drive controlled single-phase motors, like an air conditioner or a heat pump. For such applications, F type RCD would be required. These RCDs would be able to withstand smooth superimposed DC residual current ranging up to 10mA. In addition, Type F RCDs can also help in detecting all the residual currents as detected by A type RCDs.  

  • Type B 

Circuits having variable-speed drive controlled 3-phase motor includes pumps, air conditioners, electric vehicle chargers, medical equipment that would require high precision movement, etc. In such cases, the residual current frequency might be greater than 50-60 Hz and non-sinusoidal components, waveforms produced from the six-pulse-bridge rectifying circuit, etc. In such a case, RCD of Type B would be needed. However, like F type RCD, even Type B can easily withstand smooth superimposed DC residual current up to a range of 10 mA and detect all types of residual current that are detected by F Type.  

Depending on your application, you can choose from a range of add-on devices to complete RCCBs, including Type SI and Type B models. However, it might be challenging to decide a suitable type for your operations; therefore, it is advisable to consult an expert before selecting an appropriate type of RCD.  

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