Key takeaways in 30 seconds
- An AFDD detects a dangerous electric arc that a standard miniature circuit breaker (MCB) and residual current device (RCD) might not notice.
- We distinguish between a series arc (along a single conductor) and a parallel arc (between conductors); the AFDD analyses current disturbances typical for them.
- In Poland, AFDDs are RECOMMENDED by the installation standard, not mandated by law.
- It does not replace an MCB, RCD, surge protective device (SPD), periodic measurements, or repairing a faulty connection.
- Repeated tripping is a signal to call an electrician, not to bypass the device.
What is an electric arc and where does it come from?
An electric arc is a discharge that maintains current flow through air or carbonised material where the current path has been broken or damaged. It generates a lot of heat, which is why an arc can burn insulation and initiate a fire, even when the circuit is not overloaded.
This is facilitated by loose or damaged connections (a loose terminal), a torn or frayed wire, and damage to the insulation between conductors. These are causes that an electrician identifies and resolves during inspections and measurements - do not diagnose them yourself, as this requires working live.
Series arc vs. parallel arc
A series arc occurs along a single active conductor, at a break in the current path (a broken wire, a loose connector). Its current is limited by the impedance of the load, so it remains small and within normal load limits - neither an MCB nor an RCD usually detects it.
A parallel arc occurs between two conductors, line and neutral (L-N) or line and protective earth (L-PE), and is accompanied by an increase in current. An L-PE arc is sometimes partially detected by an RCD, while an L-N arc is not reliably recognised by classic protection devices. This is the gap that the AFDD fills.
How an AFDD recognises a dangerous arc
An AFDD constantly "listens" to the current waveform and analyses its frequency content (spectral analysis, commonly based on the FFT transform). A burning arc leaves a characteristic signature: a series arc generates very high-frequency oscillations (in the range of hundreds of kHz), while a parallel arc generates stronger pulses in a lower band.
The art lies in distinguishing a dangerous phenomenon from normal operation. Many appliances (vacuum cleaner brush motors, dimmers, switch-mode power supplies) themselves generate crackles resembling an arc. Therefore, the AFDD evaluates the entire signature of the disturbance over time, rather than a single pulse, and trips the circuit only after recognising the pattern of a sustained, dangerous arc.
Designs: stand-alone and integrated devices
The product standard allows for several designs, selected according to the space in the distribution board:
- Stand-alone AFDD, with its own circuit-disconnecting element.
- AFDD integrated with a miniature circuit breaker (AFDD+MCB) - arc detection plus conductor protection against overload and short circuit.
- AFDD integrated with a residual current breaker with overcurrent protection (AFDD+RCBO) - arc detection plus residual current and overcurrent protection in a single module.
The choice of design is determined by the design and available space, not by the user.
What an AFDD does NOT replace
An AFDD detects specific arc phenomena and that is all. It does not take over the tasks of:
- a miniature circuit breaker (MCB), which protects the conductor against overload and short circuit,
- a residual current device (RCD), which reacts to residual current, i.e. leakage to earth,
- a surge protective device (SPD), which limits overvoltages from discharges and switching,
- correct installation and firmly tightened connections,
- periodic measurements and resolving the actual cause, such as a faulty connector.
Product standard and installation document
It is worth separating two documents. The product standard PN-EN IEC 62606 describes the device itself: how it is to be constructed and tested in a laboratory. It covers devices for rated voltages up to 440 V AC and currents up to 63 A; in homes, single-phase versions for around 230 V are usually found. The installation standard PN-HD 60364-4-42 (protection against thermal effects), on the other hand, specifies where and when such a device should be used. Compliance with the product standard does not in itself create an obligation to install it.
Is AFDD mandatory in Poland?
There are many simplifications circulating here, so let us separate the layers:
- Law: the regulation on technical conditions to be met by buildings (WT, consolidated text Dz.U. 2022 item 1225 as amended - Polish Building Law) does not impose an obligation to use AFDDs in Poland.
- Polish standard PN-HD: the implementation of PN-HD 60364-4-42 (older edition with amendment A1:2015-01) contains clause 421.7 along with an annex, which RECOMMEND the use of AFDDs. A recommendation is not a mandate - the designer or investor decides.
- Newer IEC edition: internationally, a newer edition IEC 60364-4-42:2024 (Edition 4.0) has been published. It expanded the provisions on AFDDs and moved them to a new clause 426 (adding clause 427 - protection against internal arcing in switchgear). In Poland, it has not been implemented as a PN-HD nor referenced in the regulations, so it does not create an obligation.
- Design and insurer: an AFDD is sometimes included in a developer's specification or rewarded with a lower premium. This is a contractual requirement, not a general regulation.
- Manufacturer's instructions: indicate the conditions for selecting the device, the installation method, and the operation of the TEST button.
- Good practice: an AFDD is a recommended fire protection device, especially where the consequences of a fire would be severe.
The standard gives examples: sleeping areas (hotels, care homes, schools, apartments), locations with increased fire risk, buildings made of combustible materials. This is an increased risk, not an absolute obligation. More in the post on protection in a wooden house.
Who detects what: MCB, RCD, AFDD, SPD
| Device | What phenomenon it detects or limits | What it does NOT do |
|---|---|---|
| MCB (miniature circuit breaker) | Overload and short circuit in the circuit (protects the cable) | Does not react to leakage current or series arc |
| RCD (residual current device) | Residual current, i.e. leakage to earth or PE | Does not protect against overload and short circuit (unless RCBO); does not reliably detect L-N arc |
| AFDD | Dangerous series and parallel arc | Does not replace MCB, RCD, SPD, correct connections or measurements |
| SPD (surge protective device) | Surges from discharges and switching, diverts energy to PE | Does not protect against overload, leakage or arc; does not replace a lightning protection system |
Limitations and selection for the circuit
AFDD is selected for a specific circuit, its rated current and the nature of the loads; it operates within a defined current and voltage range, and with unusual loads, it may react differently than expected. Its effectiveness cannot be reproduced with a standard meter during periodic measurements, as the testing methods are laboratory-based.
Treat the tripping of the AFDD as information, not a device fault. Repeated trips mean that something in the circuit requires checking by an electrician - do not bypass the device or replace it with a standard circuit breaker.
Most common misunderstandings
"AFDD is mandatory in Poland." No. The installation standard recommends it, and the actual requirement may result from the design or an agreement with the insurer, not from legal regulations.
"AFDD will replace my old fuses and a proper installation." It will not. If you are worried about worn-out protection devices, take a look at the post about old screw-in fuses; AFDD is an addition, not an installation overhaul.
When to ask an electrician to check the installation?
Book an inspection and measurements if you notice: a burning smell or scorch marks near sockets, sparking or crackling, a hot socket casing, smoke or repeated tripping of protection devices without an obvious cause.
If the symptoms are clear, turn off the power to that circuit and call an electrician. Do not open the distribution board, do not tighten anything under voltage and do not perform measurements yourself - arc diagnostics requires knowledge, qualifications and equipment.
Summary
AFDD is a precise addition to fire protection: it detects a dangerous arc that standard protection devices might not notice. However, it does not replace a miniature circuit breaker, residual current device, surge protective device, good installation or measurements. In Poland, it is recommended by the standard, not mandated by law, and is most cost-effective where the consequences of a fire would be severe.
Want to be sure? At ENERTIA, we will perform an inspection and measurements of the installation, verify the selection of protection devices for your circuits and assess whether an AFDD makes sense in your case and in what version. You receive the result as a documented assessment with clear recommendations, without pressure or scare tactics. Book an inspection with measurements: book a visit online or call +48 459 566 991.
FAQ: most common questions
How does AFDD differ from an RCD?
An RCD reacts to residual current, i.e. leakage to earth or the protective conductor. AFDD recognises the signature of an electric arc, including a series arc, which is not a leakage and does not raise the current above the protection threshold. These are two different mechanisms that complement each other.
Does AFDD also protect against circuit overload?
An AFDD alone does not. Protection against overload and short circuit is provided by a miniature circuit breaker. Therefore, integrated AFDD+MCB and AFDD+RCBO versions, which combine several functions in one module, are popular.
I have a wooden house, do I have to install AFDD?
There is no such absolute legal obligation. However, combustible construction increases the importance of protection against thermal effects, which is why the standard clearly recommends AFDD in such buildings. The decision should be based on the design and risk assessment for the specific building.
The AFDD trips frequently, what should I do?
Do not bypass it and do not replace it with a standard circuit breaker. Repeated trips mean that something in the circuit requires checking. Note which device this occurs with and book an electrician for an inspection and measurements.
Can I check the AFDD with the TEST button?
You can press the TEST button in accordance with the manufacturer's instructions; it confirms the correct operation of the tripping mechanism. However, this does not replace the measurements carried out by a qualified electrician as part of periodic testing.
Will an AFDD replace a surge protective device?
No. An SPD limits overvoltages, for example from lightning strikes and switching operations, and discharges their energy to the protective conductor. This is a different task than arc detection, so both devices play distinct roles.
Sources and legal basis
Verification date: 18 July 2026.
- ISAP - Rozporządzenie w sprawie warunków technicznych, jakim powinny odpowiadać budynki i ich usytuowanie (t.j. Dz.U. 2022 poz. 1225 ze zm.) (opens in new tab)
- IEC - IEC 62606: General requirements for arc fault detection devices (AFDD) (opens in new tab)
- IEC - IEC 60364-4-42:2024 (Edition 4.0): Low-voltage electrical installations - Protection against thermal effects (opens in new tab)
- PKN - PN-HD 60364-4-42:2011 oraz PN-HD 60364-4-42:2011/A1:2015-01 (Polish version) (opens in new tab)
- Eaton - Guide to IEC 60364 standard: Low-voltage electrical installations (AFDD) (opens in new tab)
- elektro.info - Fire protection using RCDs and arc fault detection devices (opens in new tab)
- Kanał elektryczny - Electrical switchboard in a block of flats: what protections are required? (opens in new tab)
- Portal Elektryka - AFDD protections (opens in new tab)
