I think AJ has summed it up perfectly! Even if it were accepted that they might contribute to a reduction in the risk of fire, that law of unintended consequences that AJ speaks of, might cause the opposite affect. Can you put two 3.4Kw storage heaters on a 2.5? Do you really need 2 RFCs? Are you allowed to have one lighting circuit for the whole house? Can I put the immersion heater on the RFC? Such questions are likely to be considered by contractors as they seek every way possible to reduce the need to shell out for an AFDD.

Good points here I think.  The energy used by these devices is significant. At a time when we need more than ever to eliminate waste we should be very sure of the benefits before adding these constant small loads to the system. 

The extra costs of fitting these devices and the space that they require will result in essential upgrades not being done and may well reduce the average quality of installations. 

In my view the committee needs to ensure that the case is really well made and produce the evidence transparently if they are going to mandate change of this nature.  I would be more convinced if insurers showed more interest in the matter but as buildings insurance seems to be uninterested in the condition of the electrical installation I think we can assume its not the principal driver of claims.

These devices are a useful addition to the designers armoury but simply being able to fit them isn't justification for having to.

With over twenty years of hands on experience working in people’s homes I would say from observation that the circuits most susceptible to parallel arc faults in people’s homes are the lighting circuits.


This is because lighting circuits cables are usually the only circuits in loft spaces and often under insulation in locations where they are extremely prone to vermin damage. It is not at all unusual to find cable insulation stripped by vermin on lighting circuits and you will find far more damage such as this on lighting circuits than any other type of circuits.


So if I were to recommend the installation of AFDD to a circuit, the lighting circuits would be the first I would recommend them for, but the proposed regulation 421.1.7 (vi) says they are circuits AFDD can be omitted from in domestic properties.


Lighting circuits also serve sleeping accommodation, which is where people are generally most vulnerable in their homes.


So the the proposal says that AFDD can be omitted from what I consider to be the most vulnerable circuits that serve the locations where people are most vulnerable, because they are asleep.


Presumably the AFDD can be omitted from domestic lighting circuits because of the high risk of nuisance tripping from switching causing series arc, so the omission is allowable due to lack of reliability of AFDD rather that lighting circuits being low risk.


As an example, a couple of years ago I prepared an EICR for a customer at the request of his insurance company with his home being a straw thatched cottage, I had to replace sections of lighting circuit cables in the loft due to vermin damage. These were the only vermin damaged cables in the house that I could find, yet they would be the only circuits in that house that AFDD could possibly be omitted from. Being a thatched cottage increases the risk, but vermin damage in lofts is not unique to such properties and is common in homes of all types of construction within loft spaces.


The whole proposal to make AFDD compulsory seems inappropriate, but to then say they are not required on domestic lighting circuits appears to be stupid, other than it being because the devices will not perform reliably on these circuits.


Andy Betteridge

Perhaps given what they seem to be tested with, it is carbon arc lamps that are the let down that mean they cannot be used on lighting circuits.

Joking aside, I think the devices are of uncertain benefit. I recall when RCDs were first being sold to the general public, and from memory it would be the late 1970s early 1980s  there were a great many ' this man was killed by his lawnmower cable, if he had an RCD he would be here today,' and later  more upbeat 'the RCD saved my life'  sort of adverts, but there was also clear information about how they worked, what the did and did not protect against, and in terms of regulations time (about quarter of a century)  was allowed for plenty of anecdotal eveidence to build up, before they became more or less mandatory in the regs for all socket circuits for use by ordinary folk in the early 2000s.

I see an indecent haste with AFDDs on 240V circuits to force their uptake via a standards route, rather than by allowing them to be adopted on technical merit based on genuine  evidence from use in the field.

I am sorry to say I strongly suspect the unseen hand of the manufacturers pressing on the soft flesh of the standards writers, presumably keen to recover the expenses of their engineering efforts in the 20 years before the patents expire and the second tier makers are able to knock them out at a tenner each as they now do with RCDs. Commercially it makes sense, but from a regulatory perspective, anything but.


You only need to watch the tests of John Ward and others, using copper contacts and jiggling wires rather than carbon arc, to see that these devices are fine tuned to pass the spec, not to provide a realistic safety function.


As a bit of an aside the carbon /copper arc is not a logical choice -  the physics of electromigration of metal at high current density mean that arcs between loose wires made of near pure metals tend to result the connection either blowing clear or welding shut, so sustaining a steady arc at loose contacts is actually not what happens. (put a clean copper rod in the arc welder and see how difficult it is to strike compared to chalk clad steel.... it will either stick or the arc will die)


This does not happen in carbon, which burns away to CO2, nor does it happen with metals with a lot of impurities and certain types of alloy that pin the metal nucleii like some steels and some hard alloys used for relay contacts that are designed to withstand arcing without contact welding or arc erosion.

As an aside this is also why connections made by twisting wires, at least ones of pure metals,  work as well as they do, despite initial contact being struck at a few microscopic high spots, as once current starts to flow,  at these high spots - tens of atoms across in some cases, apparently eye watering  initial current densities, millions of amps per square cm, which are high enough to move the metal about to either make or break the connection.  Of course if when it stops sizzling it only makes a good ohmic contact  to one strand of a 7 strand conductor, this removes the voltage and shuts off the process for other parallel strands, but the single stand may then get far too hot - but that is not a sustained arc causing the wire and terminal to burn, just local resistance heating due to the small cross-section..

Genius move to say they can be omitted from the one circuit that they might actually be of any use on due to vermin damage

Have a look at https://www.youtube.com/watch?v=L6ZXH2a_0Vs to see a Hagar AFDD not detecting an arc from about 4 mins in. The commentary is in French which I do not speak so it may be that their electricians are as skeptical about the effectiveness of AFDDs as many here.


In a report on electrical fires in America (https://www.nfpa.org/News-and-Research/Data-research-and-tools/Electrical/Electrical)

 it says 

• Arcing was the heat source in approximately three of five home fires involving an electrical failure or malfunction.

In another document it mentions arcing in nearly every cause of an overeating by damaged cables.


Given the implication that arcing is present in nearly every case of overheating the case for AFDDs is clear. This was used as the argument in another document, I cannot now find, for the introduction of AFDDs in USA. However I cannot find any figures saying how electrical fires have decreased since their introduction. If there are some figures they are not as easy to find as the claims made about the lives that will be saved by the introduction of AFDDs. 


I can see an increase work for Bodgit and Scarper. Who is going to pay for a new consumer unit incorporating AFDDs at over £1000  with all the paperwork when B&S will do it for a £600 without any paperwork or AFDDs.


Would an AFDD have stopped the tumble dryer fires or the fridges that caught fire, it is a genuine enquiry as I do not know. 

AFDDs

Looking at changes in the new wiring regulations for Ireland  The NSAI published the 5th Edition National Rules for Electrical Installations, IS 10101:2020 on 6 March 2020. This replaced the 4th Edition, ET 101:2008.


The say on AFDDs Clause 421.7

Arc Fault Detection Devices (AFDDs) will now be recommended for circuits installed in locations with particular risk, such as;


in premises with sleeping accommodation;

in locations with risks of fire due to the nature of processed or stored materials, i.e. BE2 locations, (e.g. barns, wood-working shops, stores of combustible materials);

in locations with combustible constructional materials, (example = wooden buildings);

in fire propagating structures

in locations with endangering of irreplaceable goods

safeelectric.ie/.../

electric.ie/.../


Question:

In the UK. As most of the New domestic  Dwellings and social Housing going up now are wooden construction on a concrete base with a single brick wall on the outside, will these installations need AFDD?


The now called Irish Regulations, also require Fireproof cables to be used in wellings.

Also, frown on metal comsumer units being used, you can read for yourself.

JCM

I have just had an interesting case today. I have just changed the RCD in a CU because it failed. The CU was of Steeple brand, somewhat old. An RCD of this brand is unobtainable, so I fitted one of Hager make which is mechanically interchangeable. Some will shout about not using different brands in type-tested assemblies but will be unable to say why this matters to the RCD. However, imagine this was after amendment 2. The cost to the customer would probably be around £3k for a new CU with all the bells and whistles which are now required! Is this reasonable? Clearly the answer is no. Imagine one needed a new engine in a car because a new timing belt was needed and we had this type testing nonsense in place. Would that ever happen? Never.

in premises with sleeping accommodation;

in locations with risks of fire due to the nature of processed or stored materials, i.e. BE2 locations, (e.g. stores of combustible materials);

in locations with combustible constructional materials, (example = wooden buildings);

in fire propagating structures

in locations with endangering of irreplaceable goods


That describes bedrooms under lofts full of stored personal items, often of great sentimental value and well as financial.