Choosing the right RCD – Type A, B, F comparison
Residual current devices (RCDs) are life-saving protective devices in every electrical installation. They detect fault currents in milliseconds and interrupt the circuit before a fatal electric shock can occur. But which type is right for which application? Type A, B, F or even a special EV-RCD for wallboxes? This comprehensive guide explains everything important about selecting RCDs.
⚡ Safety notice
Work on electrical systems may only be carried out by qualified electricians. This guide is for information purposes only and does not replace professional planning or installation according to standards.
What is an RCD and how does it work?
An RCD (Residual Current Device) is an automatic protective switch that monitors differential currents between live and return conductors. As soon as a fault current exceeds the rated residual current, the RCD trips within milliseconds and disconnects the circuit from the mains.
The RCD uses a summation current transformer: All current-carrying conductors pass through a magnetic ring. As long as forward and return currents are equal, their magnetic fields cancel out. However, if part of the current flows via an unintended path, a magnetic imbalance occurs and the RCD trips.
RCD types in detail
Type A – Standard for households
Type A is the most common RCD used in most residential buildings. It detects sinusoidal AC fault currents and pulsating DC fault currents typical of modern electronic devices.
Typical applications:
- Washing machines, dishwashers, dryers (devices with phase control)
- Dimmable LED lights and electronic ballasts
- Standard sockets in living areas, kitchen, utility room
Type F – Enhanced availability
Type F is an evolution of Type A with improved resistance to nuisance tripping. It has a brief delay (approx. 10 ms) for high inrush currents, preventing unwanted tripping.
Typical applications:
- Industrial systems with frequent switching operations and high inrush currents
- Systems with many electronic consumers (data centers, office buildings)
Type B – For DC fault currents
Type B is the most universal RCD. In addition to Type A characteristics, it also detects smooth DC fault currents and mixed currents from power electronic devices with frequency converters or inverters.
Typical applications:
- Photovoltaic systems with inverters
- EV charging stations (wallboxes) with AC and DC fault current detection
- Industrial frequency converters, UPS systems, servo motors
Rated residual currents (trip currents) selection
10 mA – Enhanced personal protection
For areas with increased risk: bathrooms (especially near bathtub and shower), outdoor sockets, mobile equipment outdoors.
30 mA – Standard for personal protection
The most commonly used rated residual current. Mandatory for all socket circuits up to 20 A and all final circuits in residential buildings. Reliably protects against fatal electric shock.
100 mA – Fire protection
Used when no direct personal protection is required, but only fire protection through detection of insulation faults. Typical for main lines or upstream protective devices.
300 mA – Fire protection in large systems
For large electrical systems and main distributions to detect insulation faults and prevent cable fires. Does not provide direct personal protection.
Selection guide: Which RCD for which application?
| Application | Recommended type | Rated residual current |
|---|---|---|
| Residential area (sockets, lighting) | Typ A | 30 mA |
| Bathroom (sockets in protection zone) | Typ A | 10 mA |
| Kitchen (dishwasher, washing machine) | Typ A | 30 mA |
| Wallbox for EV (charging station) | Typ B / EV | 30 mA |
| PV system with inverter | Typ B | 30-300 mA |
| Commercial systems with many consumers | Typ F | 30 mA |
Practical tips for installation
1. Regular functional testing
Test your RCD at least every 6 months with the TEST button. It must trip immediately. If not, it is defective and must be replaced.
2. Observe selectivity
In larger systems, stage multiple RCDs: e.g. a 300 mA RCD in the main distribution and 30 mA RCDs in sub-distributions.
3. Type B not always necessary
Many modern wallboxes have integrated DC fault current protection. Then a cheaper Type A + additional DC protection often suffices.
4. Beware of nuisance tripping
Frequent nuisance tripping can indicate a defective RCD, faulty installation or actual insulation problems. Have this checked by an electrician.
Conclusion: The right RCD saves lives
RCDs are essential safety devices in every modern electrical installation. The choice of the right type depends on the connected consumers: Type A for classic household areas, Type B or EV for e-mobility and photovoltaics, Type F for industrial applications.
Remember: Regular functional tests with the TEST button are mandatory – only this ensures your RCD will trip reliably in an emergency.