Cable entry to 'non combustible' consumer units

Moving further on in my consumer unit replacement exercise I have just been looking at my 18th Edition 'On-Site Guide' and it says in section

(c) The cable installation entry method shall, so far as reasonably practical, maintain the fire containment of the enclosure. It is essential that account be taken of the manufacturer's instructions, if any.

This can generally be achieved by the installer ensuring that cable access holes in the enclosure do not leave gaps greater than:-

• 1.0mm for the horizontal top surface and * 2.5mm for all other surfaces of the enclosure that are accessible after installation

.....

How can one possibly manage this with flat T&E cable? Do new CUs come with oval cut-outs sized for T&E - it seems rather unlikely. Would any trunking used to cover cables as they enter the CU also have to be 'non-combustible'?

I'm aiming to mount the CU fairly high up, about 75 to 100mm from the ceiling. Nearly all the cables will be coming down from above, through the plasterboard ceiling. Would it satisfy the regulations to encase the whole space between the CU and the ceiling in metal?

I believe the answer is intumescent goo - fortunately I have no personal experience.

Squishy grommets

There are also glands suitable for flat cables eg

" It's rubber, it's pliable, it fits well, what more can I say. "

I wonder what some people are using them for, I've never felt the need to soften them in warm water before using.

Owain

Here is what I am doing on the CU in the garage

Richard