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 miss.
- 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, an AFDD is RECOMMENDED by the installation standard, not mandated by law.
- It does not replace an MCB, RCD, surge protective device (SPD), periodic testing, or repairing a faulty connection.
- Repeated tripping is a signal to call an electrician, not to bypass the device.
What an electric arc is and where it comes 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 releases 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 rectifies during visual inspection and testing - do not diagnose them yourself, as this requires live working.
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 connection). Its current is limited by the load impedance, 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 an 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 impulses 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 disturbance signature over time, rather than a single impulse, and only trips the circuit after recognising the pattern of a sustained, dangerous arc.
Designs: standalone and integrated devices
The product standard allows several designs, selected according to the space in the consumer unit:
- Standalone AFDD, with its own circuit-breaking 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 project and available space, not 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 cable against overload and short circuit,
- a residual current device (RCD), which reacts to residual current, i.e. earth leakage,
- a surge protective device (SPD), which limits overvoltages from discharges and switching,
- correct installation and securely tightened connections,
- periodic testing and removing the actual cause, for example a faulty joint.
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 with a rated voltage up to 440 V AC and current 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, states 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 oversimplifications 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 poz. 1225 as amended) does not impose an obligation to use AFDD in Poland.
- Polish standard PN-HD: the implementation of PN-HD 60364-4-42 (older edition with amendment A1:2015-01) contains provision 421.7 along with an annex, which RECOMMEND the use of AFDD. 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 AFDD 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 PN-HD nor referenced in the regulations, so it does not create an obligation.
- Project and insurer: AFDD is sometimes included in the developer's specification or rewarded with a lower premium. This is a contractual requirement, not a general regulation.
- Manufacturer's manual: indicates the conditions for selecting the device, the method of installation and the operation of the TEST button.
- Good practice: AFDD is a recommended fire protection measure, especially where the consequences of a fire would be severe.
The standard gives examples: sleeping areas (hotels, care homes, schools, flats), premises with increased fire risk, buildings made of combustible materials. This is an increased risk, not an absolute obligation. Read 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 it is an RCBO); does not reliably detect L-N arc |
| AFDD | Dangerous series and parallel arc | Does not replace MCB, RCD, SPD, correct connections or testing |
| SPD (surge protective device) | Overvoltages from discharges and switching, discharges energy to PE | Does not protect against overload, leakage or arc; does not replace a lightning protection system |
Limitations and circuit selection
An 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 non-standard loads it may react differently than expected. Its effectiveness cannot be reproduced with a standard tester during periodic testing, as the test methods are laboratory-based.
Treat the tripping of an AFDD as information, not a device fault. Repeated tripping means that something in the circuit needs to be checked 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 any 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, check out our post on old fuse-links; AFDD is an addition, not a rewiring of the installation.
When should you ask an electrician to check the installation?
Book an inspection and testing 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 the affected circuit and call an electrician. Do not open the distribution board, do not tighten anything under voltage, and do not carry out measurements yourself - arc diagnostics requires knowledge, qualifications, and proper equipment.
Summary
AFDD is a highly effective addition to fire protection: it detects a dangerous arc that standard protection devices might miss. However, it does not replace an MCB, RCD, surge protective device, proper installation, or testing. In Poland, it is recommended by the standard rather than mandated by law, and it is most cost-effective where the consequences of a fire would be severe.
Want to be sure? At ENERTIA, we will carry out an inspection and testing of your installation, verify the selection of protection devices for your circuits, and assess whether an AFDD makes sense in your case and in what configuration. You will receive the result as a documented assessment with clear recommendations, with no pressure and no scare tactics. Book an inspection with testing: book a visit online or call +48 459 566 991.
FAQ: frequently asked questions
What is the difference between an AFDD and an RCD?
An RCD responds to residual current, i.e. leakage to earth or the protective conductor. An 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 an AFDD also protect against circuit overload?
An AFDD alone does not. Protection against overload and short-circuits is provided by an MCB. That is why integrated AFDD+MCB and AFDD+RCBO versions, which combine several functions in a single module, are popular.
I have a wooden house, do I have to install an AFDD?
There is no such absolute legal obligation. However, a combustible structure increases the importance of protection against thermal effects, which is why the standard explicitly recommends AFDDs in such buildings. The decision should be based on the design and a 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 tripping means that something in the circuit needs checking. Note down which appliance triggers it and book an electrician for an inspection and testing.
Can I check the AFDD with the TEST button?
You can press the TEST button in accordance with the manufacturer's instructions; this confirms that the tripping mechanism is working. However, this does not replace the testing carried out by a qualified electrician as part of periodic inspections.
Will an AFDD replace a surge protective device?
No. An SPD limits overvoltages, for example from lightning strikes and switching operations, and diverts 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.)
- IEC - IEC 62606: General requirements for arc fault detection devices (AFDD)
- IEC - IEC 60364-4-42:2024 (Edition 4.0): Low-voltage electrical installations - Protection against thermal effects
- PKN - PN-HD 60364-4-42:2011 oraz PN-HD 60364-4-42:2011/A1:2015-01 (Polish version)
- Eaton - Guide to IEC 60364 standard: Low-voltage electrical installations (AFDD)
- elektro.info - Fire protection using RCDs and arc fault detection devices
- Kanał elektryczny - Consumer unit in a block of flats: what protective devices are required?
- Portal Elektryka - AFDD protection
