Recommend to me means that the default is to install unless it can be risk assessed out. 

so yes, we should default to installing AFDDs unless we can bring in other control measures that we are happy with in terms of safety. 

Recommend to me means that the default is to install unless it can be risk assessed out. 

so yes, we should default to installing AFDDs unless we can bring in other control measures that we are happy with in terms of safety. 

No Neil, you are making a serious mistake. You have misunderstood the way the regulations actually work, and the video referred to above is absolutely wrong. You need to refer first to 421.1.7 (Brown book). This is the regulation which uses shall, which means you must, with the conditions.

Then you get the the next part of 421.1.7 (after note 1 which is the small print ONLY)

This then says that it is recommended to fit them in all other premises, this from BS7671 is that it is a choice, which should be made by the CLIENT, not the electrician or someone else. It is not a case of "Risk Assessment" or anything else (you will note those words are missing), it is a simple choice. You are seeing a difficulty where there is none, my definition is "If you want to pay you can fit them which is permitted in all cases, but you can choose to spend the money or not". Simple enough.

I am not going to talk about any technical reasons why they may or may not be useful, but I suggest you study the American fire statistics since AFDDs became mandatory about 12 years ago in their code, and tell the rest of us if there is a statistical difference, I make no comment.

GK cannot say this as he is a member of JPEL/64, but I will as I am not, if you had any idea how many man-hours had been wasted on getting those words in the text as written and not something else you would probably have died a sad death from old age whilst waiting for the next agenda item!

Hi David,

I do not subscribe to allowing unqualified persons a say on items that have been recommended to be installed by those that are qualified.  We can all choose where we wish to fall on the line of compliance and I try and be at the end of 'best practice' as often as I can.  For me, if a Standard 'recommends' I install something then I need a good reason not to.  For me, 'because the client said no' is not a good enough reason to keep me where I want to be on my imaginary line of compliance.

We do not need to go into the science behind AFDDs and if they work on stranded cables etc as I have had many discussions on the subject with those far smarter than I will ever be and to be honest it does not really change how we deal with the term 'recommended'.  

I agree it is a choice to fit them in other examples but it is how we inform that choice which is important.  When I carry out a design risk assessment I will look at things like installation method, past history of EICRs, past history of electrical fires, how the building is maintained etc.  these are all things that could reduce the level of risk of an electrical issue caused by arcs and could mean that I, as the designer deems that AFDDs are not required.  I have then read the Standard, considered the risk, documented the risk and issued the DRA with my design for total transparency.  

This is how I believe we should approach the design process as competent electrical engineers.

Hi Neil

I see that you believe that the wording of this regulation was inadequate, and therefore should have been simply to require AFDDs on every circuit of every installation, because this would have been "safer", whatever that means, and it means many different things to many groups of people. Perhaps you would care to comment on the prevalence of arc faults which are not cleared by other circuit protective devices, and the number of such that cause fires? I would point out that unless you have this data it is impossible to carry out a competent risk assessment, because you have no idea of the actual risk, only a vague idea that there must be some.

The greatest risks to an installation are loose or resistive connections and so far AFDDs have not been shown that they can detect either, and in fact no one can without an inspection process that is thorough.Most installations have loose connections or screws when properly inspected, yet few of them catch fire. It takes a loose tails cable and a large load current in most instances, and these can all be seen to be resistive loss by the spread of the heat along busbars and similar parts.

I suspect that you have not considered the physics of an arc, it is very much more complex than often imagined. The fundamental part is the distance in air through which electricity can jump cold, it is a small fraction of a millimetre per thousand volts, air being a very good insulator. The mechanism is that the air must be ionised, and is then somewhat conductive. Once the conductive path is established, the next mechanism is heating of the air and ends of the electrodes, which produces many more ions at a higher temperature and the arc current can increase significantly. The ends of the electrodes then burn away, increasing the arc length, which may well then be extinguished, or possibly cause ignition of something nearby. Note that copper electrodes need to reach more than 1083C to start to produce ions, so most arcs extinguish long before this temperature is reached unless between tiny points, the heat loss with copper cables being very high due to the thermal conductivity. There is a fairly low temperature source of ions and this is heated plastic which carbonises at a fairly low temperature and has poor thermal conductivity. This is what is simulated in the AFDD demonstration equipment, but is very difficult to simulate with a real length of cable.

I wonder which part of this reasoning you feel makes AFDDs mandatory? Certainly the manufacturers do, but that is to be expected as profits would be huge, there are around 40 Million installations in the country and perhaps an average of 6 or 10 circuits each, so perhaps 400 Million units over perhaps 10 years, and £100 each? Fantastic! Yet very few of those installations would have an arc based fire, and there are many other causes of fires. Are we sure that this is the most important thing to change? Perhaps not.

David,

You seem to be putting words in my mouth which is a little impolite if I may say.  I have not commented saying that I think the regulation is worded inadequately in either a direct or indirect way.  I am very happy how it has been worded and believe that balance has been well achieved.  The onus of selecting AFDDs for the installations that are recommended sits with the designer and they are free to tackle this how they see fit using BS 7671 as their guide.  I am not sure there is any appetite for BS 7671 to be a front to back instruction manual as engineering should have choice, or it is just a book anyone could follow with no engineering knowledge required.  

I also never suggested AFDDs are mandatory, they are not for installations that fall outside the 'shall' requirements.  

And if the customer is prepared to pay for the new A.F.D.D.s.

Z.

In a reply in the comments section for the video, efixx state that the doing nothing is not an option, comment, came from the person who wrote the definition of recommended in the regs.