new out building

I take it that you intend burying the supply cable?
I would leave a hole in the bottom run of the blocks for the cable to be able to run on top of the concrete.
Just knock a corner off of one of the blocks, about 2 to 3 inches square.
You could cut a section out of the base of the block in th middle if you have the right tools.

 

Could you use some form of ducting?

 

Any cable is supposed to be buried about 450mm below the surface of the garden. As Jit says, running some ducting underground (and putting a couple of pull ropes in it) will help. It can then either come through the block work below ground level and into the out building (I'm assuming the floor hasn't been cast/done yet) or possibly come up the outside of the building and enter at/ or near ground level. Might be an idea to get a sparky to run the cable now before you start the block work and/or get him to advise after a site visit.

 

There's no specific depth (excepting in Agricultural installations), other than being deep enough so as not to be damaged.

 

I stand (or sit at my computer) corrected.

 

A bit deeper than a spades' blade length would be good.

 

So what depth would that ambiguous depth be then spin?, assuming one could use a teaspoon and hit the cable or a jcb!, so anything between nowt and, well whatever, good old 7671 as foolproof as ever.

 

Just googled for an answer and most suppliers seem to require the cable is 450mm below the surface, with the marker tape 150mm above it.

Edit,, BS 7671 would seem to suggest 500mm.

 

No it just states" a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground."
I don't know if you can get any more ambiguous?

Caravan pitches and agricultural installations where there is vehicular traffic, 0.6m.
Arable or cultivated land, 1m.

 

Hmm This thread from 2004, possibly shows how much the regs have changed http://community.screwfix.com/threads/req-deph-for-burried-cable.25983/

PS the IET seem to recommend 500mm.

 

2004 was the 16th edition.
There was no minimum depth for underground cables at caravan pitches, other than to install them outside of areas where tent pegs or ground anchors may be driven, or provide additional mechanical protection.
No minimum depth for Agricultural installations.
The quote I provided in the other post has the same wording as was used in the 16th.

 

Whatever is most convenient.

 

If you know the position of the CU and can predict the exact position of the inside wall, then a suitable sized plastic conduit (at least twice the diameter of the intended armourd cable) with a "slow" bend from 400mm below ground to a position below the CU. If any doubt about the positioning of the building on the slab then bring the armoured through the wall when the building is in place (or angle drill the slab)

 

Although this refers to Western Power Distributions criteria

A trench 530mm deep and 300mm wide, the trench should be level and free from any sharp stones or objects which could damage the service cable. the reinstated with 75mm stone dust, or ducting obtainable from the WPD office

 

Instead of the 75mm stone dust are you allowed to use coarse sharp with say 50mm of that covering the cable, and then say 50mm of 10mm pea on top of that and then marker with say 50mm sharp on top of that, and then backfill to ground level Jit?

 

The instructions Jit has provided are for Western Power operatives when laying network cables.
I imagine other DNO's have similar instructions which may or may not include stone dust, sand or whatever.

 

These may be of help to others ?
I know it is for SSE but others will be very similar if not identical

 

Hi spin , you are quite right in that the depth for our cable runs need to be over 1000mm on productive agricultural land .
And most of the DNO's I have worked with are quite happy with either sieved soil back fill or even just the previously excavated material being used without sieving as long as it is free from sharps and reasonably crumbed .