The whole thing about recommendations being just one of several possible ways to skin a cat only holds water when there actually are other ways of skinning it. There just isn't when it comes to AFDDs.

I can see some possible arguments. If we use wiring systems where damage to a line conductor that would result in arcing would very likely also cause an earth fault (BS 8436 cables, or singles in steel conduit or even simple T&E) then ordinary RCD protection will likely provide very similar levels of protection to the fixed wiring as as AFDD. Possibly ditto for accessories with earthed metallic enclosures.

Then there's an argument that if you allow an arc to start a fire, an acceptable level of safety might still be maintained by other means - e.g. suitable fireproofing in the surrounding environment - or just that the environment itself naturally isn't as risky as those listed (e.g. due to the limited number of vulnerable people that could be affected by a single event). AFDDs aren't going to stop all fires after all - they can't detect simple resistive heating - so there's the issue of diminishing returns and there soon comes a point where the additional safety just isn't worth the cost (if there's money to spare, better to spend it on more effective safety measures).

i read a "recommendation" very similarly to "consideration shall be given" (e.g. in 559.5.1.208 - for N at light switches) - i.e. have a think about it, but there's no compulsion for the moment.

    - Andy.

It is a play on words which provides the grist for lawyers. In the Real World, the likelihood of a AFDD stopping a fire is remote.

Another thing I was wondering about recently was how robust these things will actually turn out to be in the field, especially the multi function variants. All those sensitive electronic bits in close proximity to an arc chute designed to extinguish extremely high fault current when functioning in over current mode.

Then we get to the fact that they won't protect anything downstream of a transformer.

However, no matter how fancy and tortuous a language they wish to dress it up in, BS7671 is non-statutory, and good luck to any lawyer who tries to prove that the absence of such devices enabled a fire to start.

It is a play on words which provides the grist for lawyers. In the Real World, the likelihood of a AFDD stopping a fire is remote.

Another thing I was wondering about recently was how robust these things will actually turn out to be in the field, especially the multi function variants. All those sensitive electronic bits in close proximity to an arc chute designed to extinguish extremely high fault current when functioning in over current mode.

Then we get to the fact that they won't protect anything downstream of a transformer.

However, no matter how fancy and tortuous a language they wish to dress it up in, BS7671 is non-statutory, and good luck to any lawyer who tries to prove that the absence of such devices enabled a fire to start.