Residual current circuit breaker (RCD) + 5 typical faults

In this article, you will learn all about these small but very effective devices. You will find out what RCDs are, how they work and why they are so important.

After reading this article, you will understand why it is worth investing in a residual current circuit breaker.

They are particularly important when it comes to the safety of people. We explain why this is the case and what you should bear in mind!

What is that?

RCD stands for "Residual Current Device" and is a device that is used to protect against electric shocks in the event of malfunctions in the electrical system. RCDs can be found in many homes and businesses and can help to prevent serious or fatal electrical accidents.

Functionality

It trips at the latest when the rated residual current is reached and disconnects all poles of the affected circuit from the upstream network - including the neutral conductor in the case of four-pole switches. The internal test circuit is also switched off, as its current limiting resistor is not designed for continuous operation (faulty operation). The protective conductor is not part of the residual current circuit breaker and is not switched off.

Residual currents occur when part of the current flows back to the power source via an undesired current path. Part of this current path can be the protective conductor, the housing of electrical equipment, the earth including all metallic structures in electrical contact with earth and the body of a person or animal. The residual current circuit breaker forms the arithmetic sum of all instantaneous values of the currents in the phase conductors and the neutral conductor. In a system without an earth fault, the sum is always zero.

The RCD is an innovative device that uses summation current transformers to detect and eliminate residual currents. This product is designed in such a way that it prevents magnetic flux in the transformer core and therefore does not induce any voltage. If a residual current now flows back to the current source via such an unwanted current path, the sum of all currents through the summation current transformer is no longer zero. The RCD is therefore able to detect and eliminate residual currents quickly and efficiently.

The RCD is a high-quality summation current transformer that will help you to detect AC residual currents or pulsating DC residual currents. This transformer is frequency-dependent and works like a transformer. It can therefore only detect AC residual currents or pulsating DC residual currents. In the case of smooth DC residual currents, there is no transmission, i.e. no induction in the secondary winding - the residual current is not detected. In a mixed form (smooth DC residual current superimposed by AC residual current), the AC residual current can only be transmitted weakly or not at all, as the iron core is partially or completely saturated by the smooth DC residual current.

The all-current sensitive RCD is a state-of-the-art device developed to detect DC residual currents. It has a second transformer core equipped with a Hall sensor to detect the magnetic field directly. In addition, the RCD has further electronics to better detect frequency responses and their current dependencies, for example, and thus offer different types for the corresponding application.

Types

There are different types of RCD circuit breakers that can be used for different purposes.

Type AC

The residual current circuit-breaker type AC is designed to detect purely sinusoidal AC residual currents. The function is ensured if a smooth DC residual current does not exceed the value of 6 mA. (No longer permitted in Germany.)

Type A

The type A residual current circuit-breaker not only detects the usual residual currents, but also pulsating DC residual currents. This switch is the most commonly used type for normal applications.

Type A AP-R

The residual current circuit-breaker type A AP-R is a fully functional circuit-breaker that is particularly insensitive to unwanted tripping. Thanks to the short-time delayed function, the switch does not trip even in the event of minor faults, thus protecting your system from damage.

Type F

The type F residual current circuit-breaker is the perfect protection for your home or office. It has full type A AP-R functionality to detect pulse current with DC components of maximum 10 mA. It can also detect mixed frequency currents up to 1 kHz.

Type B

The type B residual current circuit-breaker is an advanced switch that detects smooth DC residual currents. This function is ensured when different types of residual currents are superimposed - regardless of the phase angle, polarity or the sudden or slow increase in current. Type B is also referred to as an all-current sensitive switch.

Type B+

The residual current circuit-breaker type B+ is a further developed model of type B. In addition to the functionality of type B, sinusoidal AC residual currents are detected for frequencies up to 20 kHz. Type B+ is therefore used for preventive higher-level fire protection. The circuit breaker is able to detect the smallest currents and thus ensure effective protection against fire.

What is the test button for?

RCDs are installed in many homes and buildings to protect occupants from the dangers of residual current. However, they are not perfect and can still make mistakes. To ensure that your RCD is working properly, you should test it regularly.

To test the RCD circuit breaker, you must first press the test button. This is normally located on the front of the appliance. If the RCD is working correctly, it should break the circuit.

If the RCD is not working properly, this may be because it is defective or has not been installed correctly. In this case, you should replace it immediately.

What is the advantage of an RCD?

RCDs are an essential part of electrical safety. They automatically switch off the power supply as soon as a fault is detected in the circuit, for example due to a short circuit or a fault in an electrical device. This prevents people from being injured by the electric shock. RCD circuit breakers are therefore an important preventive measure against accidents and electrical damage.

The 5 most common mistakes made when installing RCDs

1st fault: The RCD is not connected to the main power source

The RCD should always be connected to the main power source. This is the only way to ensure that the switch interrupts the power supply if a fault occurs. If the switch is not connected to the main power source, it may not be able to interrupt the flow of electricity if a problem occurs.

2nd fault: The RCD is not connected to all loads

The RCD should be connected to all loads so that it can interrupt the flow of current if a problem occurs. If the switch is not connected to all loads, it may not be able to interrupt the flow of current if a problem occurs.

3rd fault: The RCD is not correctly aligned

The RCD should be aligned so that the tripping mechanism is triggered correctly when a problem occurs. If the switch is not aligned correctly, it may not be able to interrupt the flow of current if a problem occurs.

4th fault: The RCD is not correctly dimensioned

The RCD should be sized so that it can interrupt the flow of current if a problem occurs. If the switch is not sized correctly, it may not be able to interrupt the flow of current if a problem occurs.

5. error: The RCD is not installed correctly

The RCD should be installed in such a way that it can interrupt the flow of electricity if a problem occurs. If the switch is not installed correctly, it may not be able to interrupt the flow of electricity if a problem occurs.

Conclusion

The RCD residual current circuit breaker is a really important device that helps to save lives. Many people do not know how important this circuit breaker is and underestimate its effect. Yet it is a very effective means of preventing electrical accidents and increasing safety.