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..

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..