AFDD Arc Fault Detection: Where Arc Protection is Now Mandatory
AFDDs (arc fault detection devices) detect arc faults in the house installation before they lead to fire. Since 2018, VDE 0100-420 has required AFDDs in certain areas. This overview shows when AFDDs are mandatory and what to look for when choosing.
How an AFDD works
AFDDs analyze the current signal for high-frequency patterns typical of arc faults.
Serial arc
Caused by loose terminals or broken wires. Classic MCBs don't detect this.
Parallel arc
Short-circuit-like between conductors. Hard to detect since the current is often below MCB trip levels.
Detection technology
Microprocessor analyzes the current waveform 1,000 times per second, comparing it with arc fault patterns.
Where AFDDs are now mandatory
Per VDE 0100-420 (2018 edition), AFDDs are required in the following areas.
| Area | AFDD required | Note |
|---|---|---|
| Sleeping rooms | Yes | In care homes, hotels |
| Wood and straw construction | Yes | Fire load from material |
| Heritage buildings | Yes | Irreplaceable substance |
| Rooms with high fire load | Yes | Storage, archive |
| Escape routes | Yes | Hospitals, schools |
| Residential general | Recommended | Currently no requirement — frequently discussed |
Pros and cons
Advantages
- Detects fire causes that MCBs and RCDs miss
- Protection particularly in sleeping areas
- Often advantageous for insurance
Disadvantages
- Higher cost (€50-150 per circuit)
- More space required in the panel
- More frequent nuisance tripping with some loads (old motors)
Selection criteria for AFDDs
Prefer combo devices
AFDD-MCB combo (RCD/MCB/AFDD in one) saves space and money compared to individual devices.
Choose rated current correctly
AFDD must match the MCB — typically 10, 13, 16 A for lighting and sockets.
Manufacturer compatibility
When mixing with RCD/MCB devices, stick with the same manufacturer — trip characteristics must align.
Tips from practice
AFDD also where not required
Bedrooms and children's rooms are classic use cases — a safety bonus even without a requirement.
Test with old loads
Old drills, vacuum cleaners or fan heaters can cause nuisance trips. Test before commissioning.
Reset properly
Some AFDDs have fault memory. After tripping, check the cause — don't just switch back on.
Conclusion: fire protection at the highest level
AFDDs are one of the most important advances of recent years. The cost is manageable, the protection gain enormous — in sleeping rooms, AFDDs should be standard today, even without a requirement.
💡 Tip: During renovation, AFDD retrofitting is particularly worthwhile in sleeping rooms — VDE 0100-420 will probably follow suit here soon.
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