Arc Fault Detection (AFDD) — EN 62606
Arc faults cause ~25% of domestic electrical fires — and RCDs cannot detect them. Here's what AFDD does, when it's required and how to integrate it in a panel.
What is an arc fault?
An arc fault is an unintended electrical discharge (arc) across a gap or through damaged insulation. It produces temperatures of 3,000–6,000°C — hot enough to ignite wood, insulation and cable jackets. Unlike a short circuit, an arc fault may draw only slightly more current than normal, making it invisible to MCBs and RCDs.
Common arc fault causes
- • Damaged cable insulation (rodent damage, mechanical)
- • Loose screw terminals (vibration, aging)
- • Improperly connected conductors
- • Aged wiring with cracked insulation
- • Pinched cables behind furniture
Why RCDs miss arc faults
- • Arc faults are line-to-neutral (not to earth)
- • RCD only trips on earth leakage
- • MCB doesn't trip — current below overload threshold
- • Arc fault smolders slowly, fire before trip
How AFDD detects arc faults
An AFDD continuously monitors the current waveform for the characteristic signature of an electrical arc: high-frequency current pulses superimposed on the normal 50Hz waveform. It uses a microprocessor and DSP to distinguish genuine arc faults from normal interference caused by dimmers, motors and switch contacts.
Detection algorithm distinguishes:
✓ Series arc fault — intermittent contact in a series path (e.g. loose terminal). Current slightly below normal, but high-frequency signature present.
✓ Parallel arc fault — arc between conductors (damaged insulation, line-to-neutral). Higher current plus HF signature.
✗ Normal switching — motor brushes, light switch arcing, dimmer — short-duration, different HF pattern, excluded by algorithm.
EN 62606 — the standard
EN 62606 (equivalent to IEC 62606) is the test standard for AFDD. It defines:
- →Mandatory detection of series and parallel arc faults within 30 A current range
- →No trip within 500ms of normal switching operations (nuisance trip immunity)
- →Test circuit with specific arc fault generators to verify detection
- →Operating temperature range −5°C to +40°C
- →Mechanical and dielectric tests equivalent to IEC 60898 MCB standard
When AFDD is required
AFDD requirements vary by country — the EU does not have a single directive, but national codes increasingly mandate it:
VDE 0100-420:2018 requires AFDD in bedrooms, children's rooms, areas with combustible building materials, historic buildings and campsite hook-ups.
ÖNORM E 8001-1:2019 requires AFDD in all residential final circuits in new builds.
NF C 15-100 includes AFDD as a recommended option but does not mandate it.
BS 7671:2018+A2:2022 requires AFDD in student accommodation, care homes, sleeping accommodation in purpose-built buildings.
AFDD not yet required by Polish PN-IEC standards, but increasingly specified by insurers.
AFDD installation in panels
AFDDs are DIN-rail devices, typically 1 or 2 modules wide. They are installed in series on the final circuit, usually combined with an MCB (AFDD+MCB combined device available from ABB, Schneider, Eaton, Siemens):
Main incomer → RCD (Type A, 30mA) → AFDD + MCB per circuit
Or: RCBO (combined RCD+MCB) + AFDD in series — two devices per circuit
AFDD connects to DIN rail, wired in series with the circuit
Some AFDDs require a 12V auxiliary supply — check before specifying
AFDD trip indicator — visual indicator shows if trip was due to arc fault (vs overcurrent in combined AFDD+MCB)
⚠️ AFDD and KNX dimmers
KNX trailing-edge dimmers produce HF current signatures that early AFDDs misinterpreted as arc faults. Modern EN 62606-certified AFDDs are immune to leading and trailing edge dimmer signatures — but always verify compatibility before combining in the same circuit.
AFDD specified where required
We keep up with national code changes across all EU markets — AFDD, SPD and RCD requirements correctly applied for your country.
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