AMD3 requires that CU installed after 01-Jan-2016 be...
- Constructed of non-combustible material (eg, metal top & bot) OR
- Enclosed within a non-combustible enclosure (with access to equipment)
An example of a suitable enclosure material would be Plasterboard or Cement Board, Class-0 foam for the seal. There is no mention of IP rating, so cab les could exit through a Class-0 foam lined hole (watch grouping) or intume scent seal oblong suitably positioned.
A hysterical response, frankly, to a sharp increase in fires reported by th e FBU - most of which of doubtful coding and in any case a metal box isn't going to make a huge difference. If you want to counter imbecile screw tigh tening you fit a 300ma time delayed RCD upstream (integrated into smart met ers, giving a viable benefit to their ridiculous nationwide cost) to give s ome useful ACTIVE fire protection and perhaps mandate a smoke alarm right b y the CU or even in the same enclosure if applicable.
As it stands you need do nothing, and the industry is supposedly going to c ode all the old CU as "C3" rather than C1/C2 which means "fix".
It is suspected some CU may have been manufactured with a plastic base whic h excluded fire retardant additives. This is a particularly onerous omissio n where the CU claimed otherwise - re trade descriptions act. If this is th e case, the industry JPEL64 / ESF should have effected a product recall - instead of "whole nation has unfit for purpose CU" when the bulk of the pla nt uses plastic CU. UK CU were supposed to pass the 650oC glow wire test (I think only 1 of 5 tested did) and incredibly they rejected 960oC plastic w hich is routinely used elsewhere.
I personally think non-FR CU should be recalled, and if you want to do some thing about CU fire risk - fit a smoke & upstream fire-RCD (time delay 300m a). A few people used to do just that in timber frame workshops with heavy draw equipment, small price for a bit more fire protection.
If you can make any enclosure lift-off via lift-off brackets (like toilet s ervice panels) or instead machine screw fitted into boiler-rawlplugs (M6/M8 screw fits into steel tube into plastic rawling) then that is ideal.