AFDD Regulations 2024

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Important news surrounding the AFDD Regulations with the latest 18th Edition Amendment 2!

The release of AMD2 to BS7671, the 18th edition wiring regulations has introduced a requirement to use Arc Fault Detection Devices (AFDDs) on socket circuits up to 32A in certain instances.

We’ll delve into the specific instances below, however safe to say the new AFDD regulations will affect a large number of installations going forward.

They are still quite a niche thing at the moment and hence come with eye watering prices (of at least £100 per unit). Unlike SPDs which are fitted one per board, AFDDs need to be fitted on a “per circuit” basis, like RCBOs.

This will mean that the introduction of AFDD regulations into the 18th AMD2 regulations could be a costly and complicated affair for some.

AFDD Regulations - Arc Fault Detection Device - 18th Edition BS7671 AMD2
AFDD Regulations – Wylex AFDD Unit

What Exactly Does An AFDD Do?

Ok this is AFDD #101 – if you already know what an Arc Fault Detection Device does then skip forward to the next section.

If you have never come across them before, don’t panic – you’re not alone… despite their being a mention of them in the original 18th edition back in 2018, little hard and fast requirements where made.

Some electricians have been using these on specific risk properties, for example, those with thatched roofs where fire is a particular issue.

However the fact they have been used so little has meant few manufacturers have rushed products out to suit this upcoming requirement.

So an Arc Fault Detection Device (Or AFDD for short) is a small module fitted at the origin of the the circuit. Originally 2 modules wide like DP RCDs, they are now being built as MCB/RCBO/AFDD all in one single module.

They are microprocessor controlled. The electronics within constantly monitor the circuit and the loads placed upon it. The AFDD can detect parallel arcs between different conductors or series arcs within the same conductor, for instance where a wire my have broken.

AFDD Regulations - Arc Fault Detection Devices - Arcing Types
AFDD Regulations – Different Types Of Arcing

Once the AFDD has determined there is an Arc on the circuit, it trips the power supply to the circuit to remove the fault as per automatic disconnection of supply.

Arc Fault Detection Devices are able to distinguish between working arcs and those caused by a fault.

When Do I Need To Fit An AFDD?

AFDD regulations 2023 Wylex AFDD
AFDD Regulations 2023

The AFDD regulations in the 18th edition AMD2 stipulate a number of instances where an electrician must fit these devices in order to remain compliant.

Let’s start by examining Reg 421.1.7 and see what it says:

AFDDs must be fitted at the origin of any single-phase AC final circuits supplying socket-outlets with a rated current not exceeding 32 A in the following premises:

  • Higher Risk Residential Buildings (HRRB)
  • Houses in Multiple Occupation (HMOs)
  • Purpose built accommodation for students
  • Care homes

As electricians we are well used to these passages in the regulations by now, noticing that this is a “MUST” and not a “SHOULD” indicating a hard & fast requirement as opposed to a recommendation.

Let’s investigate each scenario separately:

Higher Risk Residential Buildings (HRRB)

The AFDD regulations introduced in March 2022 (with the introduction of AMD2 of the 18th edition) now place a requirement for installing them in Higher Risk Residential Buildings.

There is no clear definition of what is classed as a high risk building, however a note underneath the regulation states that this should be assumed to be a residential building which is over 18M or 6 storeys high (whichever occurs first)

This is assumed to be a possible response to the Grenfell tragedy.

Houses in Multiple Occupation (HMOs)

Houses in Multiple Occupation have had extra fire requirements over and above those for single occupier rented dwellings.

Mandatory fire doors, higher requirements for fire alarms and potentially even emergency lighting regulations all affect these type of properties.

Due to the fact that different households are sharing a single property, this can mean evacuation from the property can be more awkward.

BS7671 18th Edition AMD2:2022 requires all circuits with a rated current not exceeding 32A serving socket outlets must be fitted with an AFDD.

Purpose Built Student Accomodation

Again, similarly to HMOs, student accommodation can have particular risks which can make evacuation of the property difficult. And yes, that probably relates around drunk students!

However, these AFDD regulations only apply to ‘purpose built student accommodation, which means that existing buildings used as student accommodation will not have to comply (unless they fall into the HMO category as many student accommodation does)

Care Homes

Perhaps the most difficult of all to evacuate during a fire are care homes. Old and infirm residents can be at particular risk and hence, again, higher fire safety requirements apply to these installations.

If you ever do work in care homes then you should be acutely aware of the extra risks these properties can pose and the way in which you can reduce these risks through the electrical installation.

One of the ways that risk can be lowered is through fitting AFDDs to the circuits. AMD2 has brought a requirement for these to be fitted to socket circuits of not more than 32A. We also recommend that you consider going beyond the AFDD regulations and fit them to more circuits.

Recommendation For Other Scenarios

As stated above, there are certain other scenarios when an electrician might consider fitting arc fault detection devices to an installation.

These instances may include, but are not limited to, the following types of installations where these do not fall into the categories above:

  • Thatched roof houses due to the particular risk of fire.
  • Certain areas of particular public risk, IE: Cinema, School, etc…
  • Hospitals and healthcare facilities
  • Heritage buildings

In these instances it may be more than just circuits serving socket outlets which need AFDD protection. For example a thatched roof bungalow may need arc fault detection installing on lighting circuits and other circuits which run through the loft space.

Do I Need To Fit AFDD Protection?

The answer to the question Do I Need To Fit AFDD Protection depends on the installation

AFDD Regulations 18th Edition

In summary, if your installation fits into the 4 categories above, then you MUST fit an AFDD to any circuit less than 32A which serve socket outlets.

If the installation is not specified above, however is in a particular high risk building/site then AFDD may be recommended on certain other circuits.

Check the following resources for help with the AFDD regulations as part of the 18th Edition AMD2:

NICEIC Guide to 18th Edition AMD2

BEAMA Guide to AFDDs

23 Responses

  1. Any circuits less than 32a , means only those that are lower than 32a .
    So ring mains and other circuits off 32 and above are exceptions . Not sure I am reading this right, less than or less than and equal to?

    • Hello

      Many apologies, this was indeed unclear from myself, less than and equal to is what actually applies. So anything 32A OR less will require AFDD protection in these instances.

      I will alter the article to reflect this

      Kind regards

  2. Thanks for the above article, it’s helpful.
    Question – we’re (trying!) to sell our flat and about to complete but the buyer asked for an electrical report.
    We had an electrician round this morning who inspected and showed us we have 2 RCBOs and 5 MCBs on our board. He said we need to change the MCBs for RCBOs as a requirement to pass.
    The quote for this is £835.
    Screwfix charge a lowest price of £5 and highest of £50 for an RCBO, the average around £30 and ones that 32a Type c which that required for our ECB. That would be £150 for 5 meaning £685 for labour…this seems excessive as I have checked the labour required viewing installations online and it basically plug and play.
    I called the company and pointed out all this, they said they’d get back to me and have done with a revised quote of £553 saying “I have checked with some different suppliers and managed to find the RCBOs cheaper” well well well…. turns out they rated 2.7 out of 5 on Google (my wife booked them)
    Anyone know a reputable electrician?

    • Hello Barnaby

      Unfortunately we have heard this sort of thing before, where the inspecting electrician often charges very little for the initial report, sadly with the view to make their money on the remedial works afterwards. A number of people just take the remedial work quote on face value and end up paying dearly for very little work indeed.

      I do know of a network of reliable local electricians who you can check out here:

      The members are all part of a group trying to raise standards within the electrical industry and they can be trusted to offer proper advice.

      Hope that helps?

      Kind regards

    • if it was to be taken at face value and you only wanted a condition report, i cannot see why they have said it needs rcbos installing. rcd protection is not retrospective. the installation should be being tested to the standards to which it was installed to and not current regulations. unless it was specified to test to the latest edition etc. to be fair without seeing it it is impossible to say one way or the other but i would be getting a second test done on it at those remedial works prices.

  3. Do afdd’s require installing in an existing installation say schools, leisure centres alike or can you just recommend them on an E.I.C.R via code 3 ? Or is the installation of such devices only for new installations?

    • Hello Victor

      There is no requirement to retrofit AFDDs into existing installations. I would suggest recommending them as a C3 on an EICR for existing installations in situations where they are stipulated in the wiring regulations. These include:

    • Care Home Installations
    • Student Accommodation
    • HMOs (Houses In Multiple Occupation)
    • Hise Rise Residential Properties
    • As there is no specific requirement to install AFDDs in either schools or leisure centres, I’m not sure adding them as a C3 on an EICR would be appropriate. That being said, there is nothing to stop you specifying them on a new installation in any situation you think which may benefit from the added safety

      Hope that helps?
      Kind regards

  4. I have a pub which is at the moment unused. at the rear there is an L shaped 2 storey building consisting of 20 rooms on each floor. the rooms are for single occupancy so just a living/bed room kitchenette and bathroom in each.
    ring mains feed 2 to 3 of these rooms coming off a 3 phase board there are 4, 3 phase boards in total so they each provide lights and sockets to 10 of the rooms. there is a communal corridor with emergency lighting around the front of the building. would the socket circuits need AFDD’s on the ring mains as they seem to fall into the HMO scope as some share an RFC circuit on an mcb in the CU.
    I want to replace the boards but unsure whether or not to use a type a RCBO or put in AFDDs .

    • Hi Mike, thanks for getting in touch with the question and thanks for the detail, it helps when answering questions like these!

      From what you have described, when you replace the consumer units you would need to fit AFDDs to the circuits which serve sockets within the single occupancy rooms as these would fall under the definition of a HMO as per the latest amendment to the wiring regulations.
      It doesn’t sound as though you have any “shared facilities”, however these would also need AFDD protection if you have shared living rooms or kitchens (again, it doesn’t sound like you do but I’ll include it for others reading the answer).

      There is no requirement to fit AFDDs to any other circuits in the premises, type A RCBOs will be fine in these instances.

      Hope that helps?

      Kind regards

  5. I’ve just had an EICR done for an HMO (where I live with lodgers). I got a C3 for no AFDD’s and I’m being told I need to spend £1,400 to get a new consumer unit with AFDD’s fitted. Two questions:
    1) Is the requirement for AFDD’S retrospective for this existing installation?
    2) Can’t the MCB’s just be swopped for AFDD’s without changing the whole consumer unit?

    • Hello Jody, thanks for getting in touch with the question, it’s a very relevant one at the moment

      To answer your specific questions:

      1 = No, the requirement is not retrospective, hence why the issue has been given a C3 (Improvement Recommended) on an EICR. This particular ‘coding’ is akin to an advisory on an MOT for a car. The EICR would not be classed as unsatisfactory simply due to this matter (although there may be other issues which may cause the report to be classed as unsatisfactory). HOWEVER, any NEW installation work within the property would need to comply. So if you needed to install some new sockets, then you would need to install an AFDD on that particular circuit. If you wanted to upgrade the consumer unit (for some other reason), you would need to fit AFDDs to any circuit that supplies sockets.

      2 = Potentially yes, the MCB can be swapped for an AFDD. This would entirely depend on the consumer unit fitted. Unfortunately there are not a grand amount of different AFDDs available and hence the range available for retrofitting is quite limited. If the consumer unit is fairly modern then yes it may be possible to retrofit an AFDD for that circuit, however if it’s older then you may need to upgrade the whole unit to find one that fits. This exact problem is causing headaches with a care home customer of ours where we are having to upgrade the older distribution boards to be able to fit AFDDs as they require new sockets installing. As you can imagine, this isn’t very popular with the customer.

      I hope that was of some help? If you can reply and let me know what type of consumer unit you currently have fitted I may be able to advise a little further about whether retrofit AFDDS are available or not.

      Kind regards

  6. Hi
    I have an older consumer unit all mcb and main switch no rcd protection, I live in a 2 bed house, I had eicr done and electrician put code c3 no rcd protection and c3 plastic db, would this be correct of him or should I call him back and get 2nd opinion, thanks

  7. Hi, I live in a high rise building (45M) and all of the leaseholders have just paid for lightning protection for our building and we are now being told that we require surge protection at an additional cost of £40K, there are 170 units in the building, my question is firstly is surge protection required and secondly is £40k a reasonable cost for undertaking this work, the company has told us that they will not certify the lightning protection work without us doing the surge protection work.
    Thank you

    • Hi David, thanks for getting in touch and posting the question.

      I’ll be honest, lightning protection is a really specialised area and I don’t have a lot of knowledge about the regulations concerning this as it is totally separate to the wiring regulations.

      Surge protection for lightning strikes is known as T1 SPD (surge protection device). These are particularly expensive compared to T2 SPDs which have become more popular in domestic installs recently.

      The exact cost depends on a huge number of factors, including how the supply to each area is separated and where they will need to install the particular SPDs.

      To give some idea, if they fitted single phase T1 SPDs to each unit, these can cost about ~£150 each then you are looking at over £25k in parts alone.

      It may be that the SPD needs installing closer to the origin of the supply, where less individual SPDs may be required however the ratings of these will need to be substantially higher which will mean they will cost significantly more per SPD.

      From what you have described, it does seem a bit poor on their part that this wasn’t mentioned “up front” when you were getting the lightning protection installed.

      The only real advice I can give is to contact another local specialist (if you Google “Lightning Protection Installers”) and ask if they can give you some more idea of what you need to do and perhaps an alternative quote.

      Sorry I couldn’t be more use!

      Kind regards

  8. Hi there, if I am reading this correctly, AFDD is required on 32A or lower amp socket circuits. Does this include ring and radial? If so, does this include kitchen rings? Does the AFDD replace the MCB or RCBO or is it wise to get a combined AFDD/RCBO? Many thanks.

    • Hello Des thanks for getting in touch and posting the question

      AFDDs are required on 32A or lower socket circuits, but only in the event the premises is one of the defined categories (Care home, dedicated built student accommodation, Houses in multiple occupation or else buildings over 18M tall). If your installation is just a standard house then there is no hard and fast requirement to install AFDD protection. You can install in a house if you see fit, but AFDDs are currently very expensive and the cost can add up quickly.

      For what it’s worth though, they need to be fitted regardless of ring or radial, and yes it would include kitchen rings in those defined premises. The only difference between a ring and a radial circuit would be that the AFDD would not be able to detect a series arc in a single conductor as the current would just flow down the other leg of the ring.

      Most AFDDs come as a combined unit which is an RCBO and AFDD in one unit. That being said, there are some manufacturers which make combined MCB/AFDD without the RCBO/RCD element built in. Unless you have some really specific use in mind, I would recommend just fitting a combined RCBO/AFDD as this offers the best protection and is all wrapped up in one single module unit.

      Hope that helps?

      Kind regards
      Electrical Assistance Team

  9. Hi there
    I have a boarding house at a school that requires upgrades to the db’s whilst doing this I was thinking of fitting affd’s to the socket circuits.
    The building isn’t a purpose built boarding house but has an extension which was purpose built as a boarding house for students, this part isn’t affected by the upgrade works and has its only supply.

    Do the affd’s need to be fitted only to the student part as there is also house master living accommodation as part of the existing building
    Which also has student accommodation above


    • Hello Vince, thanks for getting in touch and posting the question.

      It’s a difficult one to advise for certain, it would depend to what extent the ‘master living accommodation’ was separate from the student accommodation.

      The closest I can use as a guide would be advice I received from the NICEIC technical helpline over a particular job in a nursing home, we needed to add some external sockets however the DB was particularly old and adding AFDDs would have required an upgrade. I was unsure if sockets which only served the area outside of the building would definitely need AFDD protection so decided to call them for some advice. The advice I received was that anything that was considered as ‘part of the nursing home’ would require AFDD protection. This included outdoor sockets, or after further questioning, for example any sockets that were part of outbuildings on the same site and could be accessed the same (my particular question related to a detached garage and any potential new sockets in there).

      The advisor said that the requirement was not just simply to protect the outlets themselves, but also the cables supplying these socket outlets.

      From what you have described it seems as though the master accommodation is part of the same building and thus it’s probably best to fit AFDD protection to any socket circuits in this location too.

      Hope this helps? Could you check what your CPS technical helpline say?

  10. Have a friend who was told that she needed to upgrade her consumer unit approx 10 years old which passed last years EICR with a new one as the electrician said that any EICR that us instructed for a HMO that AFDDs are absence is a C2 observation.

    I have read this in the latest 18th edition, but also read that the checks should be done on the consumer unit as per the edition it was installed.

    I had my own EICR done on my HMO and it cost a little over £200, electrician was at the property for 3 hours and spent time checking every socket and changing a few where needed.

    My friend has spent £1200 and when helping her trying to decorate a room, the light socket is not even attached to the wall.

    The wording seems to be so misleading, it reads like you have to have AFDDs for an EICR, yet its hard to find clear prove that if your Consumer Unit was fitted on 17th Edition, then it should be able to get an EICR without AFDDs, or put another way, you don’t need to spend another £1000.

    If anyone can help with clearer evidence that would be great as I trust my electrician but it seems my friend will continue to pay over the odds.


    • Hello Roscoe, thanks for getting in touch and sorry for the delay replying, I have been really busy with my electrical business and struggling to keep up with this project.

      With regards the absence of AFDD protection in a HMO would only attract a C3 – IMPROVEMENT RECOMMENDED item, which is not a unsatisfactory outcome without other further issues. Put simply, it wouldn’t ‘fail’ based on the absence of AFDDs alone.

      There is a lot of confusion about this, both amongst the electrical industry and landlords. It seems a lot of people have been told that an upgrade is required when an EICR is completed. Having spoke to the NICEIC technical helpline with regards this, their take is that even if a consumer unit upgrade is completed, unless a brand new circuit has been installed that would require AFDD protection, there is no requirement to install AFDD protection to existing circuits.

      Hope that helps?
      Regards – Electrical-Assistance Team

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