Type A vs. Type B residual current circuit breaker - What do you really need?
You're standing in front of the distribution box and wondering: Type A or Type B? Don't worry—you're not alone. The differences between residual current device (RCD) types are one of the most common topics in electrical installations. So let's take a closer look at it all here.
What does a residual current device (RCD) actually do?
First and foremost: A residual current device (RCD) protects people from electric shock. As soon as a fault current occurs—for example, when current flows through your body to earth—the RCD trips within milliseconds. It detects the difference between the incoming and outgoing current. Hence the name "residual current device."
However, not all residual current devices (RCDs) are created equal. Depending on the type of fault current they need to detect, there are different types. And this is where things get interesting.
An overview of the different types of FIs
Type AC - the classic (but outdated)
Type AC detectors only detect sinusoidal alternating fault currents. This was sufficient in the past because household appliances almost exclusively used resistive loads such as light bulbs or heaters. However, type AC detectors are no longer permitted for new installations in Austria and Germany. This is because they do not detect smooth direct current fault currents generated by modern electronics.
Type A - the standard
Type A detectors detect sinusoidal alternating fault currents and, additionally, pulsating direct fault currents. These pulsating direct fault currents are precisely what occurs in devices with semiconductors—that is, in practically anything that has a power supply or electronic control. Examples include washing machines, dishwashers, LED dimmers, computers, and many kitchen appliances.
Therefore, type A is now the absolute standard. It is used in most installations and is required by standards for residential buildings.
Type B - the all-rounder
Type B detects everything Type A can, plus smooth DC fault currents. These occur in devices with three-phase rectification—for example, frequency converters, certain wallboxes, PV inverters, or induction cooktops with special electronics.
Consequently, Type B is always mandatory when the manufacturer's documentation for a device explicitly requires it. This is particularly common in the commercial sector and with certain e-mobility solutions.
Type B+ - the extension
Furthermore, there is the type B+, which also detects high-frequency fault currents up to 20 kHz. However, this type is only needed in special applications and is irrelevant for most installations.
Type A or Type B for the wallbox?
That's probably the most frequently asked question in this context. And the answer is: It depends on the wallbox.
Many modern wallboxes—such as the Fronius Wattpilot—already have built-in DC residual current detection (6 mA). This means that a Type A residual current device (RCD) is sufficient. Other wallboxes without this integrated protection feature, however, require a Type B RCD or a Type A EV RCD (specifically for electric vehicles).
Therefore, always check your wallbox's installation instructions first. They clearly state which type of residual current device (RCD) is required. If in doubt, a Type B is the safer choice—albeit also the more expensive one.
Important: The decision should always be made by a qualified electrician. Especially with wallboxes, professional installation is not only recommended, but legally required in Austria and Germany.
When do you need which type? — Practical examples
To give you a better idea, here are some typical use cases:
Type A is sufficient for:
- Standard household electrical circuits (sockets, lighting)
- Washing machine, dryer, dishwasher
- LED lighting and dimmers
- Wallboxes with integrated DC fault current detection
- Computers and consumer electronics
Type B is required in the following cases:
- Wallboxes WITHOUT integrated DC fault current detection
- Frequency converters (e.g. in air conditioners, heat pumps)
- Certain PV inverters
- Machines with three-phase rectification
- Medical devices (depending on the standard)
RCBO: All in one device
Additionally, there are RCBOs (residual current circuit breakers with miniature circuit breakers) that combine residual current protection and miniature circuit breakers in a single device. This saves space in the distribution board and simplifies installation. It's a particularly practical solution where space is limited in small distribution boards.
Furthermore, a residual current circuit breaker with overload protection (RCBO) has the advantage that, in the event of a trip, it is immediately clear which circuit is affected. With a standard RCBO that protects multiple circuits, you first have to search for which circuit breaker has tripped.
Rated residual current: 30 mA or 300 mA?
Another important point: The rated residual current (IΔn) determines the residual current at which the RCD trips.
- 30 mA — Personal protection. Standard for all socket circuits in residential areas. Mandatory according to ÖVE/ÖNORM E 8001 and DIN VDE 0100-410.
- 300 mA — Fire protection. Used for main lines or distribution boards where direct personal protection is not required.
In summary: For anything where people could come into contact with electricity, you need 30 mA.
Common mistakes when selecting an FI (Fiber Optic Controller).
Finally, some typical pitfalls:
- Installing type AC is no longer compliant with standards. Avoid it in new installations.
- Too many circuits on one RCD — if the RCD trips, everything goes dark. Better: Use multiple RCDs or RCBOs (residual current circuit breakers).
- Do not match the RCD type to the consumer — always check the manufacturer's specifications.
- Do not install an RCD for the wallbox — Even if the wallbox has DC detection, you still need an upstream RCD type A (at least).
Conclusion
Type A residual current device (RCD) is the right choice for the vast majority of applications. You only need Type B if a device can generate smooth DC fault currents and doesn't have its own DC fault current monitoring. The manufacturer's documentation and applicable standards are always crucial.
If in doubt: Ask your electrician. And if you're looking for the right residual current circuit breaker (RCCB), you'll find it with us — from Hager to Schrack and Eaton to Schneider Electric .
