Learn about residual current devices

Safely disconnect the power in the event of a fault with residual current devices (RCDs) — essential in building electrical distribution boards. Here you will learn how to connect RCDs, what to do if the fuse blows, and what types of RCDs are available.

a15c00f4-cfc3-415d-b663-c83c3156e70f - pl-S22-210795-Key-Visual-Fehlerstrom-5SV1-1920x1080px original

What does an RCD do?

Also known as a ground fault circuit interrupter, an RCD is a safety device that protects people from electric shocks by immediately cutting off the power in the event of a fault current.

The RCD monitors the current flow in an electrical circuit and compares the incoming current with the outgoing current. If a difference is detected, this means that some of the current has taken an alternative path, such as through a person receiving a shock.

When does the RCD trip?

To detect and prevent faults, the RCD is equipped with a differential current transformer. This generates a magnetic flux proportional to the differential current. If the differential current exceeds a certain preset value, e.g., 30 mA, the magnetic flux becomes strong enough to trigger a switching mechanism and interrupt the circuit.

The rapid tripping of the RCD prevents people from being exposed to a dangerous current (greater than 30 mA). It is important to regularly check that the RCD is functioning correctly to ensure safety in electrical installations.

f724d59a-39f2-4451-892e-b1194f310585 - Zusaetzliche-Angebote_original.png

b569d5cc-459b-4ee1-90e2-69626d007748 - 1-Energieverbraucher-im-Haushalt-no-text-2082x1305

What to do if the RCD trips?

If the fuse blows, i.e., the RCD trips and interrupts the circuit, you should determine and fix the cause of the trip before switching it back on. Steps may include:

Check all appliances and plugs: Disconnect all appliances from the mains and reconnect them one by one to identify the faulty appliance.
Locate the fault current: Check the electrical circuit for possible insulation faults or short circuits. In such cases, an electrician should be consulted.
Switch off all circuit breakers downstream of the RCD: This ensures that no current flows to the RCD and it can be reset.
Resetting the RCD: After checking all possible sources of error, you can reset the RCD by switching it back on. However, if the RCD trips again, an electrician should be consulted.

Can I simply switch the RCD back on?

Once the cause has been rectified, the RCD can be switched back on. However, it is advisable to have this done by a qualified electrician to ensure that everything is functioning correctly and that no further risks remain.

A Siemens product image featuring a person in a blue shirt and a white background.

89cec723-5bff-4e9f-b2e6-d98721274106 - Challenge_original.png

e01c7a3d96f059e2e8ed728e46f472ba252764ad - grafik-typenuebersicht-de-fehlerstrom-schutzeinrichtungen-no-text-1920x1080.jpg

What type of RCD should I use?

It's important to use the correct type of RCD (according to local regulations and standards) installed by a qualified electrician. Such as:

Type A trips in response to both sinusoidal alternating fault currents and pulsating direct fault currents. They are primarily used for single-phase loads with integrated electrical components.
Type F: Single-phase frequency converters, such as washing machines, can generate fault currents from a frequency mixture with components in the kHz range. Type F RCDs protect against this, offering surge current withstand capability and can handle smooth DC fault currents.
Type B protect against smooth DC fault currents, use SIQUENCE all-current sensitive residual current circuit breakers 5SV3 Type B/B+ with integrated SIGRES function.

What happens if you don't use an RCD?

Without an RCD, a residual current caused by a faulty conductor, a short circuit, or an electric shock may go undetected and the risk of electrical accidents is significantly increased. This can lead to serious injuries, especially if the residual current flows through a person's body. The RCD plays a crucial role in protecting people and property from the dangers of a residual current.

50b68307-013d-4c61-b43f-5f855d84b037 - 2-Gebaudebrande-no-text-2009x1206

A person is standing in front of a Siemens building, wearing a blue shirt and holding a Siemens product in their hand.

Is it mandatory to use an RCD?

RCD requirements can vary depending on the country, region, and type of electrical installation. However, in many countries and regions, there is a legal obligation to use RCDs in certain areas or for certain types of electrical installations. In Germany, for example, the use of RCDs is legally mandated.

Which electrical circuits must be protected?

According to the German standard DIN VDE 0100-410, all final circuits up to 32 A must be protected by an RCD in residential, commercial, and public buildings.

This means that in many cases, installing an RCD is mandatory. However, the installation of an RCD is not required for all households, particularly in older buildings (grandfather clause). The exact requirements depend on the type of installation and the specific regulations.

It is strongly recommended to have an RCD in your electrical installation and to regularly check that it is functioning correctly. A qualified electrician can assist with installation and testing.

0f1197e9-9f53-4a87-a72f-99c2e0700ac6 - Folie1-no-text-shero-2560x1440

Is it possible to retrofit and connect to an RCD?

In most cases, it is possible to retrofit an RCD into an existing electrical installation.

An electrician will first inspect the electrical system to determine if it is suitable for the installation of an RCD. This includes checking the existing wiring, the distribution box and other relevant components.

If necessary, additional wiring or components will need to be installed to properly integrate the RCD into the system. The electrician will then connect and configure the RCD in accordance with applicable standards and regulations.

An RCD can typically last several years to decades. The average lifespan of an RCD is usually specified by the manufacturer and can vary depending on the model. However, there are some factors that can affect lifespan:

Quality: A high-quality RCD manufactured according to applicable norms and standards tends to have a longer lifespan.
Environment: Extremely high or low temperatures, humidity, dust, or chemical vapors can shorten the lifespan of the RCD.
Usage: Repeated tripping can lead to wear and tear and shorten RCD lifespan.
Maintenance: Regular maintenance and inspections of the electrical system can help to identify and resolve potential problems early, which can extend the RCD lifespan.

If there is any doubt about the RCD functionality, consult a qualified electrician.

A person wearing a hat and a backpack stands in front of a building with a large window and a sign on the wall, looking at something in the distance under a clear blue sky.