I am prepared to believe that AFDDs will spot some faults that other devices wouldn't disconnect. I am also aware that they'd likely provide some protection downstream of the fixed wiring too - say to all those £5 extension leads run behind the bed and dodgy USB chargers.


I am very dubious about the cost/benefit ratio however. I suspect the number of fires started by arcing alone (rather than say by resistive heating) is relatively small - and given the BILLIONS of pounds that would be needed to upgrade UK homes alone (never mind other installations) (say 30 million homes @ £2,0000 a pop = £60,000,000,000). My gut feel is that the money could be better spent elsewhere.


I'm also very uneasy of dictating a single solution to the arcing problem (if there is one) - I can imagine several situations - e.g. wiring in steel conduit with metalclad accessories, supplying steel cased fixed equipment where the chances of an arc starting a fire in the fabric of the building must already be vanishingly small - yet such alternative approaches don't seem to have been considered.


Then there's the law of unintended consequences ... at £2,000+ CU replacement is going to be discouraged economically - so more installations will carry on for longer with dodgy installations. The usual accessibility requirement for the actuating levers of devices to be between 1350-1450mm above floor level means we won't be able to use Euro style multi-row CUs, so we'll need a large amount of horizontal space for a CU (probably two or more enclosures side-by-side) for these multi-module devices. And as the technology seems to require one device per final circuit, there'll obviously there'll be an economic incentive to minimise the number of final circuits - with possible safety compromises as a result (e.g. loss of lighting over a wider area/stairs due to a single fault).


Were AFDDs say £5 a pop extra (over say an RCBO), were a single module wide, could be retrofitted into existing CUs, and could be shown to be reasonably resistant to nuisance tripping, and were only demanded where sensible alternatives weren't adopted, I'd probably be entirely happy with the regs to demand them. I don't think that time has arrived though.


  - Andy.

I am prepared to believe that AFDDs will spot some faults that other devices wouldn't disconnect. I am also aware that they'd likely provide some protection downstream of the fixed wiring too - say to all those £5 extension leads run behind the bed and dodgy USB chargers.


I am very dubious about the cost/benefit ratio however. I suspect the number of fires started by arcing alone (rather than say by resistive heating) is relatively small - and given the BILLIONS of pounds that would be needed to upgrade UK homes alone (never mind other installations) (say 30 million homes @ £2,0000 a pop = £60,000,000,000). My gut feel is that the money could be better spent elsewhere.


I'm also very uneasy of dictating a single solution to the arcing problem (if there is one) - I can imagine several situations - e.g. wiring in steel conduit with metalclad accessories, supplying steel cased fixed equipment where the chances of an arc starting a fire in the fabric of the building must already be vanishingly small - yet such alternative approaches don't seem to have been considered.


Then there's the law of unintended consequences ... at £2,000+ CU replacement is going to be discouraged economically - so more installations will carry on for longer with dodgy installations. The usual accessibility requirement for the actuating levers of devices to be between 1350-1450mm above floor level means we won't be able to use Euro style multi-row CUs, so we'll need a large amount of horizontal space for a CU (probably two or more enclosures side-by-side) for these multi-module devices. And as the technology seems to require one device per final circuit, there'll obviously there'll be an economic incentive to minimise the number of final circuits - with possible safety compromises as a result (e.g. loss of lighting over a wider area/stairs due to a single fault).


Were AFDDs say £5 a pop extra (over say an RCBO), were a single module wide, could be retrofitted into existing CUs, and could be shown to be reasonably resistant to nuisance tripping, and were only demanded where sensible alternatives weren't adopted, I'd probably be entirely happy with the regs to demand them. I don't think that time has arrived though.


  - Andy.