I'm wiring up my cooker hood using the same 13 amp fuse spurred off a double socket however i only have a plastic back box for the 13 amp fuse as this is what was there before. ..........The hood works for a bit then the fuse blows. ......Am i right in thinking that the plastic back box should be replaced for a metal one thus giving a better earth.......The hood wiring itself doesn't have an earth wire but im thinking that in order to get a proper earth both double and fuse box must be metal.......is this correct