An AFDD (arc fault detection device) detects dangerous series and parallel arc faults by analysing the waveform of the circuit current, and disconnects the circuit. It complements an MCB and an RCD; it does not replace them.
Why an MCB or RCD can miss a series arc: in a broken conductor or a loose terminal the arc sits in series with the load, so the current stays normal (too low for the MCB) and nothing leaks to earth, so the RCD sees no fault.
Arcing cable, but no breaker trip?
An arc carries current across a gap
At a fractured conductor or faulty contact, current can flow through an electrical discharge. Heat concentrated in a small spot can damage insulation or ignite nearby material.
MCBs and RCDs monitor different things
An MCB responds to overcurrent. An RCD compares line and neutral currents. A series arc may draw modest current with no leakage to earth, so both devices may remain on.
An AFDD recognises current patterns
Electronics look for features of hazardous arcing and initiate disconnection. The recognition algorithm accounts for normal switching sparks and brush motor operation.
On this page
Explore a fault in the cable
Choose a situation
Cable detail, enlarged
L — line · N — neutral · PE — protective conductor.
This pattern explains the idea; it is not a measurement. An AFDD analyses several features and their duration, rather than comparing current against a single number.
Broken conductor: series arc
Current supplying the appliance passes through an arc in the damaged conductor. The load limits the current, so dangerous heating can occur below the breaker rating.
- MCB · Circuit breaker
May not trip: current is below its operating threshold.
- RCCB · Residual-current protection
Does not detect this arc without leakage to earth.
- AFDD · Arc protection
Designed to detect hazardous series arcing.
The illustration shows the fault before disconnection. MCB, RCCB and AFDD functions are considered separately. Actual operation depends on current, arc characteristics, time and device. This is not a wiring diagram.
Three arrangements, different functions
AFDD as a separate function
Arc protection alone does not imply overcurrent or residual-current protection. Coordinated devices are needed; an add-on unit must use the manufacturer’s approved combination.
AFDD + MCB
Arc, overload and short-circuit protection in one device. Residual-current protection may be absent: provide the required RCD separately.
AFDD + RCBO
Combines arc, overcurrent and residual-current protection. Check rating, breaking capacity, RCD type and compatibility with the distribution board for each circuit.
Illustrations follow the devices in our editor. Module widths, terminals, buttons and functions vary by model.
Reading the device markings
AFDD / IEC (EN) 62606
Identifies the arc protection function and its product standard. AFDD alone does not identify the other built-in protections.
B16 / C16
On a device with an MCB function, 16 A is rated current and B or C describes instantaneous overcurrent operation. This is not “spark sensitivity”.
30 mA / type A
These describe built-in residual-current protection, if present. 30 mA is not an arc detection threshold, and RCD type A differs from breaker curve B/C.
TEST / T and indicator
Button functions, checking intervals and indication codes depend on the model. Follow its instructions; TEST does not certify the condition of all wiring.
Where this protection is particularly useful
Bedrooms and sleeping accommodation
A fault at night may go unnoticed for longer. Circuit requirements depend on building use and local regulations.
Combustible structures and valuable property
Timber structures and irreplaceable assets increase the consequences of fire. AFDDs complement sound wiring, fire precautions and alarms.
Cables exposed to damage
A flex trapped by furniture, ageing insulation or a poor contact needs inspection. Adding an AFDD does not make a damaged cable fit for continued use.
Whether AFDDs are mandatory depends on the country, applicable edition of the rules, building and circuit. IEC/EN 62606 is a product standard, not a universal installation requirement for every home. PlanMyPanel project rules do not replace a designer’s check of local requirements.
What to do after an AFDD trip
- 1.
If you notice a burning smell, crackling or unusual heat, stop using the circuit. Isolate safely without touching the damaged area; leave the danger zone and call emergency services if there is smoke or fire.
- 2.
Note which appliances were running and record the indication code as instructed by the manufacturer. A combined device may have tripped on overcurrent or leakage rather than an arc.
- 3.
For repeated or unexplained trips, leave the circuit off and call an electrician. Never bypass protection or create sparks as a test; the circuit and device need checking after the cause is repaired.
Common questions
Do I need an AFDD if I already have an RCBO?
An ordinary RCBO protects against overcurrent and leakage but has no dedicated arc detection function. Whether your circuit needs AFDD protection depends on requirements and risk assessment.
Can one AFDD protect the whole house?
Protection is normally provided at the origin of individual final circuits. A single incoming device is not a universal substitute: design, coordination and manufacturer instructions matter.
Will it detect every spark or hot connection?
No. Normal operational sparks must be distinguished from hazardous arcing. Overheating without a recognisable arc can go undetected; no device guarantees prevention of every fire.
Can I test it with a sparking wire?
No. Use the manufacturer’s test button and procedure. Deliberately creating an arc is dangerous and is not a valid protection test.
Where are AFDDs required or recommended?
IEC/HD 60364-4-42 recommends AFDDs on final circuits in certain situations, for example sleeping accommodation, locations with combustible construction materials or with combustible stored or processed materials, and buildings with irreplaceable goods. Some countries make them mandatory in specific cases; national rules differ, Germany does so through DIN VDE 0100-420. PlanMyPanel treats them as required in wooden houses; your electrician and local rules decide.