AFDDs for the UK are a bit of a puzzle to me.  They originate from the USA where the domestic supply voltage is 125 vac, domestic wiring uses three insulated cores, the appliance plug top usually causes the flex to drape downwards at 90 degrees from the plug top and ring final circuits (RFC) are not normally used.


Thus, USA portable appliances will draw double the nominal current of a UK appliance doing the same rated work.  This may be why the AFDD needs a minimum load of 2.5 amps and  to detect the presence of an arc before it operates.  Most domestic UK lighting installations will normally be running at less than 2.5 amps, and these installations are the ones most likely to have hidden joint boxes present.  So an AFDD would seem to be potentially an inoperative item in this application.


The UK uses two insulated line conductors with a bare cpc between them for normal domestic wiring (pvc twe in old parlance). Thus a line-to-line fault in a cable would be unusual; a fault will usually be one or both lines to earth and an RCD will clear this in a typical time of 40msecs.  So an AFDD might be useful here, but is also likely to be beaten by the operation of a fuse, MCB or RCD.


UK plug tops to BS 546 and 1363 etc. route the appliance flex directly downwards in normal use, so we don't stress the appliance flexes in the same manner as the USA, so this aspect of the hazard is much less in the UK.


AFDDs cannot detect a serial fault in an RFC, as the nature of the RFC does not propagate an arc at a loose connection.  Thus, an AFDD would only react to a parallel fault in an RFC installation, which a fuse, MCB and/or RCD will most likely disconnect anyway.  So, not much appeal to fit an AFDD for an RFC.


I understand that manufacturers are at present developing single-module RCBO/AFDD units. Oh dear!  What a clutter of little symbols to decipher in a consumer unit at Inspection time.  They typically dissipate 1 watt in operation, so a consumer unit with five or six installed will be warmer than one might wish.  And what when the device trips.............  As far as I'm aware, there is no test equipment for AFDDs at present; if one is found to be nuisance tripping, replacement seems the only option.  Not good.


Early days yet - time and the early adopters will tell.  At seemingly app. £200 each at present, this could be a slow process.


Regards,


                   Colin Jenkins.

AFDDs for the UK are a bit of a puzzle to me.  They originate from the USA where the domestic supply voltage is 125 vac, domestic wiring uses three insulated cores, the appliance plug top usually causes the flex to drape downwards at 90 degrees from the plug top and ring final circuits (RFC) are not normally used.


Thus, USA portable appliances will draw double the nominal current of a UK appliance doing the same rated work.  This may be why the AFDD needs a minimum load of 2.5 amps and  to detect the presence of an arc before it operates.  Most domestic UK lighting installations will normally be running at less than 2.5 amps, and these installations are the ones most likely to have hidden joint boxes present.  So an AFDD would seem to be potentially an inoperative item in this application.


The UK uses two insulated line conductors with a bare cpc between them for normal domestic wiring (pvc twe in old parlance). Thus a line-to-line fault in a cable would be unusual; a fault will usually be one or both lines to earth and an RCD will clear this in a typical time of 40msecs.  So an AFDD might be useful here, but is also likely to be beaten by the operation of a fuse, MCB or RCD.


UK plug tops to BS 546 and 1363 etc. route the appliance flex directly downwards in normal use, so we don't stress the appliance flexes in the same manner as the USA, so this aspect of the hazard is much less in the UK.


AFDDs cannot detect a serial fault in an RFC, as the nature of the RFC does not propagate an arc at a loose connection.  Thus, an AFDD would only react to a parallel fault in an RFC installation, which a fuse, MCB and/or RCD will most likely disconnect anyway.  So, not much appeal to fit an AFDD for an RFC.


I understand that manufacturers are at present developing single-module RCBO/AFDD units. Oh dear!  What a clutter of little symbols to decipher in a consumer unit at Inspection time.  They typically dissipate 1 watt in operation, so a consumer unit with five or six installed will be warmer than one might wish.  And what when the device trips.............  As far as I'm aware, there is no test equipment for AFDDs at present; if one is found to be nuisance tripping, replacement seems the only option.  Not good.


Early days yet - time and the early adopters will tell.  At seemingly app. £200 each at present, this could be a slow process.


Regards,


                   Colin Jenkins.