Boards

521.10.1 "Non-sheathed cables for fixed wiring shall be enclosed in conduit, ducting or trunking.   ..."

Edit; Although this reg seems concerned with degree of ingress rather than the combustibility of the materials of the enclosure.

In practice of course, it will be fine in most cases.

Regs wise it very much depends on how the board and wall are made, how rigid it all is, if it is good enough that you may consider it to create a partial enclosure such that a test finger could not reach the wires. A similar consideration applies to trunking with bits missing, or large holes in the covers, where unsheathed singles (singly insulated if you like) may be used inside the trunking so long as the enclosure is per 521.10 -  IP rating for  containment of  unsheathed cables. It says IP4X or IPXXD - but actually these are two quite different things, IPXXD relates to a test finger that is

quite fat, while IP40 is more about wires.  Actually the IPXXD trunking spec is very lax, allowing bare wires out of finger reach, but personally I'd not be happy with that, but insulated singles should be OK if you cannot reach them,

This old thread describes it quite well. 

Mike.

An outer sheath is there mainly to provide mechanical protection. In its absence, Is the wall rough bare brick/stone or smooth plaster? Are the screws holding the wood to the wall exposed? Could a cable get snagged on one of the screws? Etc.

The wall is smooth plaster and no screws protrude behind the board.   The cables would not be accessible to a finger but it would be possible to push a hacksaw blade or similar up behind the board a to damage the cable. 

To be fair if you expect hacksaw blades, then normal twin and earth may last a few seconds longer but is not going to fare well either.

In such a case it might be nicer if the access was blocked with wooden battens or something to form a definite boxed in enclosure.

Mike

What's it for dcbwhaley?

I am thinking how will the box behind, presumably sunk into the wall, be accessible for inspection? Would the board be removable and will there be enough slack on the singles? And is there a reason why you need to use singles instead of sheathed cables? 

Nearest thing I can think of this situation is in a cupboard above an inset oven where there are loads of FCUs stuck on the back wall of the cupboard. People tend to fill the cupboard with stuff and inadvertently switch off one of the FCUs, then wonder why the dishwasher isn't working. In this situation FCUs would be better situated towards the front on one side. The whole lot can also be missed in an EICR. But I digress, a bit of a sore point with me, I was called out for just such an occurrence recently, DW not working.

Edit; posted this on my phone and can't seem to delete the smileys. Please ignore all but the last one.

Nothing is sunk into the wall.  The board is 20mm clear of the wall.  Cables get behind in a drop of 2x1 mini trunking.

Singles and sheathed cables are not mutually exclusive and it should be obvious why, for a single connection, a single is preferable to T&E.

And your comparison with a cupboard above an oven baffles me.

dcbwhaley said:

Connections between the boxes will be out of the back, behind the board and back into another box.

Is why I thought there was another box behind. But you mean another of the 6. Which sort of begs the question why not have the boxes tight together and use the knockouts to run the cables

dcbwhaley said:

Singles and sheathed cables are not mutually exclusive and it should be obvious why, for a single connection, a single is preferable to T&E.

 I asked for info on what it was all for and why is it necessary to run singles. So now I have to assume you already have run singles to the board position, but I might be wrong, don't know.

As for kitchen units, ignore it.