Beama have produced a guide for AFDD's (Nov 2017), for those not seen it.
It says '
It is recommended that special measures be taken to protect against the effects of arc faults in final circuits:
• in premises with sleeping accommodation;
• in locations with risks of fire due to the nature of processed or
stored materials, i.e. BE2 locations, (e.g. barns, woodworking shops, stores of combustible materials);
• in locations with combustible constructional materials,
.e. CA2 locations (e.g. wooden buildings);
• in fire propagating structures, i.e. CB2 locations;
• in locations with endangering of irreplaceable goods.
And '
In order to implement the technical intent of the HD, Bs 7671 18th Edition will include requirements covering the use of AFDDs however the actual requirements and final wording will not be available until publication of the 18th Edition in July 2018.
So lets wait and see; but looks like you chaps doing EICR's will coding away on those recently installed A3 CU's, 'cos they won't be big enough to add AFDD's