I have been trying to wire in the last few circuits into my previously installed CU and have been having problems with the fixings.
From previous posts you may recall that barring three cables coming down the wall the rest come from beneath the floor in trunking beside the CU, and all cables enter the CU from behind. To facilitate this the CU is on stand-offs and it is these that I underestimated and have been trying to insert larger ones to accommodate the additional cables. The issue that has developed is that the wall is made of cinder "breeze" blocks and the metal wall plugs have worked themselves loose. Unfortunately the CU cannot be re-sited owing to being surrounded by meters , cutout and isolator switch further restricted by having to fit under a worktop. So what are my options?

One option is to embed studding into wall securing it with epoxy or car body filler. Are these fire rated?

Second option is to fit a ply or chipboard back board feeding the cables behind with holes to match the cable entry holes. Advantage of this is that it gives me options to find sound fixing points in the wall and screwing the CU to the board. it would alleviate some of the issue of having to feed the cables into the CU before securing to the wall as it is the weight of the cables that causes the above issues of pulling out the plugs before the CU can be firmly secured. I have seen plenty of CUs attached this way inside exterior service boxes. Would this now meet current fire ratings?

Option three having seen CUs mounted on drywalling I presume PB is regarded as adequate fire rated. I could cover the board in option 2?

The plan was/is to seal all gaps and openings with fire rated foam to ensure the integrity of the CU.

I would be grateful for any opinions on my proposals or any alternatives. Currently the CU has only wired with the original circuits and is precariously hanging off two not so secure screws, so no pressure

Richard