The CU/DB (consumer Unit / Distribution Board) should use Main Switch & RCBO and not MCB.  Consider the cable from the house to the shed.  SWA (Steel Wire Armoured) is normally used, worth considering using something like Docaster EV ultra it can deliver power a data via cat 6 in one neat bundle to the shed.  Use it for WiFi.

Depth of cable if buried at least 500mm below glound will add 1 meter of length to your cable.  Then do cable calculation with volt drop to confirm.  To be honest this is the role of the designer which will probably be your electrician. 

"The CU/DB (consumer Unit / Distribution Board) should use Main Switch & RCBO and not MCB. "

It certainly could - I think to say should which implies must is a bit strong, certainly there should be RCD/RCBO protection somewhere, but that could be at the house supply end.
It rather depends what is going in the garage eventually, if for example it really needs separated power and lights circuits, or if it needs data cable as you suggest for that matter - it is nearly twice the price of the normal SWA of the same capacity.

What you describe may be a bit more gold plate than is needed.

Also if there is any chance in the future that there may be an EV charger or a service that needs bonding (like a water pipe) then the decision to export the house earth or to make a TT island needs to be made, as indeed the total load and the distance will determine the cable size in the normal way.

Mike.

worth considering using something like Docaster EV ultra it can deliver power a data via cat 6 in one neat bundle to the shed.  Use it for WiFi.

I'm not sure that'll meet BS 7671 requirements for 100mm separation of buried power and comms cables (528.2). (To be honest I'm not that keen of twisted pair inside the same sheath/armour of mains cables even above ground.)

   - Andy.

AJJewsbury said:

Docaster EV ultra

Below is from the EV_Ultra_Datasheet

So they say, but I still don't see how that meets the requirement for 100mm separation, or "a fire-retardant partition... between cables, e.g. bricks cable protecting caps (clay,concrete), shaped blocks (concrete), protective cable conduit or troughs made of fire-retardant materials)" for cables underground.

   - Andy.

you could ask them that question

Well it does not need to, as the makers instructions take over from what is after all a generic standard aimed at keeping bell wire out of the consumer unit and similar stupidity - the same 'problem' could be seen with the wiring for every phone, pabx and fax machine but it is solved. 

In this case Doncaster are the ones to whom you pass the blame ;-)   You should be careful at the ends however, what you do not really want is to be stripping and terminating the network and mains ends in terminals in the same box.

If need be a dummy box with nothing in it but glands, where the data and power cables are split their separate ways, is a neat way to handle that one.

The EMC  concern is interesting and hard to prove, but I can believe it causes very few problems in practice.

Mike.

the same 'problem' could be seen with the wiring for every phone, pabx and fax machine but it is solved. 

But they're not (usually) underground - which is what 528.2 is aimed at.

Even above ground I usually see something a bit more substantial between data and mains side than a single layer of basic insulation and the data cable sheath (a sheath on the LV cable for instance, or a bit of clear space)

    - Andy.

True and it feels better with a bigger gap.- but if that basic insulation on the mains wire, and the cable sheath on the data cable had been tested to the same flash test voltages as the other 3 phase cores, then a lot of that worry should abate.

I agree it may 'feel' wrong, but I'm pretty sure it is no more dangerous than many other things we are unused to and do not like, that on close inspection are OK really, like perhaps the two phases behind one light switch without a 400v label, or the sockets in bathrooms moving ever closer, that UK folk get upset by.

It is (as often with these sort of things) in the hands of the manufacturers.

Mike.

True and it feels better with a bigger gap.- but if that basic insulation on the mains wire, and the cable sheath on the data cable had been tested to the same flash test voltages as the other 3 phase cores, then a lot of that worry should abate.

I agree it may 'feel' wrong, but I'm pretty sure it is no more dangerous than many other things we are unused to and do not like, that on close inspection are OK really, like perhaps the two phases behind one light switch without a 400v label, or the sockets in bathrooms moving ever closer, that UK folk get upset by.

It is (as often with these sort of things) in the hands of the manufacturers.

Mike.