The Arc Fault Detection Device… again.

The point though Andy, is do these "connections" cause fires? In the normal case, they do not (Chris's lathe wiring did not think about catching fire) because the dissipated energy is very low. To start a fire needs a significant amount of energy, even if the materials nearby are very flammable. The only case where this is not true is vapour fires from something like petrol. which has a very low flashpoint (ie. required energy) to ignite. From all of these videos, one can see that the dissipated energy is very small and that mechanical movement is also a requirement to start an arc. These two things together are very rarely present in fixed wiring. It is not possible to start an arc unless there is a source of ions (charged particles which can carry a current) and these come from vapourised metal or conductive liquids (or carbon rods), and these sources are very unusual in fixed wiring. Those with an arc welder may like to try an experiment. Set it to the lowest possible current setting, say 30A or less. Chose a clean piece of bare metal rod as an electrode and a clean surface to strike an arc. Can you get anything to happen? Answer: just some sparks. If you hold the rod a fraction of a milimetre from the surface does an arc start: no? If the rod touches the surface does an arc start: no, you simply get a short circuit? If you use a carbon rod in place of the metal one can you start an arc: yes. Does this simulate a real fixed wiring situation: no. That is why the standard uses a carbon rod, it is the only realistic way to start a low current arc, by providing an ion source. The standard test is fatally flawed! That is why there are no fire improvement statistics from America, there is no reduction in fires.


The science behind these devices is simply not there, and it is easily shown that these devices are being sold to detect a problem which does not exist. The situation in which they may trip are NOT likely to start a fire, and those which might start a fire do not exist in a fixed installation. Existing protection measures, the CPD and an RCD provide protection against most faults very well, and AFDDs would not help where they fail. I challenge anyone to show any mechanism which allows an AFDD to be useful in a real installation which is not already involved in a fire or other extreme situation such as flooding. The manufacturers are strangely quiet, except saying that the software is still being "improved". Unfortunately, there is nothing much that these devices could improve. I see no reason at all why a single device should not protect a whole installation either, except that detecting an arc on a circuit with a stable 60A load would be even more difficult. The only situation which might be improved is a high current loose connection like loose tails connections, but we have already dealt with that alleged problem!

The point though Andy, is do these "connections" cause fires? In the normal case, they do not (Chris's lathe wiring did not think about catching fire) because the dissipated energy is very low. To start a fire needs a significant amount of energy, even if the materials nearby are very flammable. The only case where this is not true is vapour fires from something like petrol. which has a very low flashpoint (ie. required energy) to ignite. From all of these videos, one can see that the dissipated energy is very small and that mechanical movement is also a requirement to start an arc. These two things together are very rarely present in fixed wiring. It is not possible to start an arc unless there is a source of ions (charged particles which can carry a current) and these come from vapourised metal or conductive liquids (or carbon rods), and these sources are very unusual in fixed wiring. Those with an arc welder may like to try an experiment. Set it to the lowest possible current setting, say 30A or less. Chose a clean piece of bare metal rod as an electrode and a clean surface to strike an arc. Can you get anything to happen? Answer: just some sparks. If you hold the rod a fraction of a milimetre from the surface does an arc start: no? If the rod touches the surface does an arc start: no, you simply get a short circuit? If you use a carbon rod in place of the metal one can you start an arc: yes. Does this simulate a real fixed wiring situation: no. That is why the standard uses a carbon rod, it is the only realistic way to start a low current arc, by providing an ion source. The standard test is fatally flawed! That is why there are no fire improvement statistics from America, there is no reduction in fires.


The science behind these devices is simply not there, and it is easily shown that these devices are being sold to detect a problem which does not exist. The situation in which they may trip are NOT likely to start a fire, and those which might start a fire do not exist in a fixed installation. Existing protection measures, the CPD and an RCD provide protection against most faults very well, and AFDDs would not help where they fail. I challenge anyone to show any mechanism which allows an AFDD to be useful in a real installation which is not already involved in a fire or other extreme situation such as flooding. The manufacturers are strangely quiet, except saying that the software is still being "improved". Unfortunately, there is nothing much that these devices could improve. I see no reason at all why a single device should not protect a whole installation either, except that detecting an arc on a circuit with a stable 60A load would be even more difficult. The only situation which might be improved is a high current loose connection like loose tails connections, but we have already dealt with that alleged problem!