The £1300 AFDD consumer unit

davezawadi (David Stone):

We have lightning protection which might work, but not if the spike is bigger than a minor disturbance, with a seriously reactive method of earthing, working against a very low impedance source (the mains supply), which means that spike clipping will be marginal at best. In a real installation, it is unlikely that any of these devices could clip an 8/20 spike (the test standard) with a current of a couple of kA and limit the voltage to 4kV, because of the connection inductance and earth resistance. This is a peak power of 8MJ, roughly the same kinetic energy as a car has moving at 100 m/sec stopping dead. Not a lot left of that! Perhaps I am being unfair and these lightning spikes are much smaller and of much less energy, in which case why do I need these devices? The LV directive says that electronics must withstand 4kV low energy spikes, so what am I protecting, perhaps slightly bigger spikes but not much bigger! The incidence of such is not clear or documented, just some arbitrary amount of LV line above ground depending on the area living density. This seems to be aimed at induced current from nearby ground strikes, but have you ever had one near you? Again only high exposed trees usually suffer, and there are few of these in Lincolnshire although there are a lot of overhead lines, so a lot of surge protection.

All the SPDs I've fitted, in cases where there were impulse problems damaging equipment, with LV and EMC Directive compliant equipment, that solved that problem permanently, must have been a dream then?

SPDs are NOT intended to address direct strikes at or close to an installation.

davezawadi (David Stone):

We have lightning protection which might work, but not if the spike is bigger than a minor disturbance, with a seriously reactive method of earthing, working against a very low impedance source (the mains supply), which means that spike clipping will be marginal at best. In a real installation, it is unlikely that any of these devices could clip an 8/20 spike (the test standard) with a current of a couple of kA and limit the voltage to 4kV, because of the connection inductance and earth resistance. This is a peak power of 8MJ, roughly the same kinetic energy as a car has moving at 100 m/sec stopping dead. Not a lot left of that! Perhaps I am being unfair and these lightning spikes are much smaller and of much less energy, in which case why do I need these devices? The LV directive says that electronics must withstand 4kV low energy spikes, so what am I protecting, perhaps slightly bigger spikes but not much bigger! The incidence of such is not clear or documented, just some arbitrary amount of LV line above ground depending on the area living density. This seems to be aimed at induced current from nearby ground strikes, but have you ever had one near you? Again only high exposed trees usually suffer, and there are few of these in Lincolnshire although there are a lot of overhead lines, so a lot of surge protection.

All the SPDs I've fitted, in cases where there were impulse problems damaging equipment, with LV and EMC Directive compliant equipment, that solved that problem permanently, must have been a dream then?

SPDs are NOT intended to address direct strikes at or close to an installation.