Power to remote garage - conduit and cable and feasibility

[Stevos]

Hi,

I'm currently planning on laying a patio (which has to be done quite soon), but in the future I'd like to be able to run power to a garage on the other side of it. When that happens I don't want to be digging up the patio.

I suspect I can't afford either the cost of the electrical work now, or the associated BCO / paperwork / signoff pain, but I'm trying to plan for the future as much as possible and avoid problems later.

The power requirements for the garage will be perhaps a couple of double sockets and some kind of lighting. I may want to run a fridge/freezer and ~3kW power tools, but won't to be doing heavy workshop stuff, and definitely no prospect for converting it to living space.

Consumer unit is about 10m from the back wall of the building - garden length is about 11m, with a lawn section, and a hypothetical patio at the end. Both buildings have single skin brick wall at those edges.

I seem to have a few possible options, and am struggling to evaluate how reasonable / sane / legal / cost effective they are

1) Dig a 2-3ft trench along the garden, run conduit with rope for pulling cable, and warning tape, fill in and lay patio. Persuade an electrician to run the cable and installation at both building ends at a later date.

2) Dig a 2-3ft trench along the garden, run cable (10mm 3 core SWA?) and warning tape, fill in and lay patio. Persuade an electrician to use this cable later

3) Do both of the above (SWA in conduit - though I'm not sure which conduit would be big enough)

4) Do nothing now, and try later to persuade an electrician to run cable as needed along the fence line (concrete fence posts and kick plate)

5) Do nothing now, and try to get it done with suspended cable later (not keen on this approach)

6) Pay someone now to make the whole problem go away by putting in all the electrical work with trenches etc as needed.

7) Give up on the whole thing as too expensive and difficult, and move house to somewhere with power already in the garage

I've read around a bit, but haven't managed to work it out yet. I'd appreciate any thoughts on how reasonable these options sound, whether an electrician would be likely to be okay with using pre-installed cable / conduit (which sort?), and whether it's actually feasible for a DIYer to get the trenches done properly...

Many thanks

 

[bernardgreen]

Lay in a duct for the cable to be installed later.

Same rules apply, 450 mm deep and warning tape.

Minimum internal diameter 32 mm. No sharp bends,

 

[Stevos]

Thanks for the suggestion.

I've been struggling to find appropriate duct (both in terms of finding what the product is, and availability). Would you be able to link to something suitable (or give a product name?)

Thanks

 

[winston1]

1/. No.
2/. Possible, but 10 mm seems over the top.
3/. SWA does not need to go in conduit.
4/. No, cables should not be on a fence.
5/. No.
6/. Yes.
7/.

 

[JohnW2]

Lay in a duct for the cable to be installed later. ... Same rules apply, 450 mm deep and warning tape. ... Minimum internal diameter 32 mm. No sharp bends,

... to which I would add, if you took that approach, take plenty of photos, with a measuring stick in place, so that you could hopefully subsequently convince an electrician that the ducting was satisfactorily installed (particularly as regards depth and presence of warning tape), throughout its length, for him/her to run cable through.

Kind Regards, John

 

[riveralt]

Lay in a duct for the cable to be installed later.

Same rules apply, 450 mm deep and warning tape.

Minimum internal diameter 32 mm. No sharp bends,

Why does it have to be 450mm deep?
Its only going under a patio after all.

The only reference I can remember to underground cable depth was for agricultural purposes or a caravan site and these varied between a minimum of 600mm and 1000mm.

 

[JohnW2]

Why does it have to be 450mm deep? Its only going under a patio after all.

Indeed. All that 522.8.10 says is that buried cables, conduits and ducts "shall be at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground". If it were literally all under a patio, one could argue that even very close to the surface satisfied that requirement.

The only reference I can remember to underground cable depth was for agricultural purposes or a caravan site and these varied between a minimum of 600mm and 1000mm.

Yes, IIRC, those are the only places in the regs where depths are explictly specified.

Having said that, this 450mm figure seems to be widely thrown about as a 'general requirement' for buried cables, but I don't know where it comes from. I can't find it in my old (red) OSG. Anywhere where digging is a "foreseeable possibility", it probably would not be very safe (hence not compliant with 522.8.10) if it were a lot less than 450mm - I would guess that around 350mm would probably be the minimum that would be relatively safe in such a situation.

Kind Regards, John

 

[Simon35]

Thanks for the suggestion.

I've been struggling to find appropriate duct (both in terms of finding what the product is, and availability). Would you be able to link to something suitable (or give a product name?)

Thanks

http://www.pipes-underground.com/cable-ducting.html

http://www.draindepot.co.uk/40mm-x-50m-black-twinwall-electric-cable-duct.html

http://www.qvsdirect.com/cable-mark...n=googlebase&gclid=CKbju-33ucUCFQzJtAod0hQAMw

 

[Stevos]

Why does it have to be 450mm deep?
Its only going under a patio after all.

Sorry - I wasn't clear - The hypothetical cable run will be under a lawn at the house end, and under a patio or decking at the garage end (original post updated).

I wasn't sure if the "reasonable depth" was specifically defined. I assume I'll want to go for a happy medium between deep enough to be clearly safe, and not so deep that I break my back digging it...

 

[JohnW2]

... The hypothetical cable run will be under a lawn at the house end, and under a patio or decking at the garage end (original post updated). ... I wasn't sure if the "reasonable depth" was specifically defined. I assume I'll want to go for a happy medium between deep enough to be clearly safe, and not so deep that I break my back digging it...

As I said, although one sees this 450mm figure thrown around a lot, the regs don't seem to explicit define what they regard as an acceptable depth. However, as I also said, in situations in which digging is a possibility, even if a very unlikley one (so that probably includes ground which is currently laid to lawn {but theoretically may not always be}), I would think that it needs to be a least "a spade and a bit", which is probably 350mm or thereabouts (to the top of the cable or duct).

Kind Regards, John

 

[Stevos]

Thanks for the suggestion.

I've been struggling to find appropriate duct (both in terms of finding what the product is, and availability). Would you be able to link to something suitable (or give a product name?)

Thanks

http://www.pipes-underground.com/cable-ducting.html

http://www.draindepot.co.uk/40mm-x-50m-black-twinwall-electric-cable-duct.html

http://www.qvsdirect.com/cable-mark...base&gclid=CKbju-33ucUCFQzJtAod0hQAMw[/QUOTE]

Perfect - exactly what I was looking for, thanks. For some reason my google-fu was failing me. I think it's not really sold directly for consumers / idiots like me

I assume it would look something like this:

https://sketch.io/render/sketch5550cdab8f7eb.png

Wobbly lines unintentional (but may be representative of digging skill too...)

In terms of avoiding sharp bends, next to the wall, it must be shallower than the stated depth right?

I assume if I have the duct (or SWA) come out vertically next to the wall, an electrician would be able to suitably terminate it and pass whichever cable is required through the wall.

 

[plugwash]

Why does it have to be 450mm deep? Its only going under a patio after all.

Indeed. All that 522.8.10 says is that buried cables, conduits and ducts "shall be at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground". If it were literally all under a patio, one could argue that even very close to the surface satisfied that requirement.

One could, one could also argue that gardens do get rearranged and so a cable anywhere under a garden should be deep enough to stay out of the way of reasonable gardening.

 

[JohnW2]

If it were literally all under a patio, one could argue that even very close to the surface satisfied that requirement.

One could, one could also argue that gardens do get rearranged and so a cable anywhere under a garden should be deep enough to stay out of the way of reasonable gardening.

That's true, and I wasn't really offering it as a serious 'suggestion' - my primary point being that the regs only require a 'sufficient depth' - not this magical 450mm we keep hearing about. Having said that, if it were very shallow, the warning tape could probably actually be on the surface, so immediately obvious to anyone who lifted the patio. Mind you, I fairly recently discovered that in the house of a family member, SWA going to a shed is laying on the ground immediately underneath some patio slabs (again, immediately obvious to anyone who lifts the slabs) - and, given that it's been like that for at least 25 years, I'm in no hurry to suggest or make any changes!

Kind Regards, John

 

[ban-all-sheds]

Patios, particularly if the pavers are bedded in mortar (or indeed if the patio is concrete) could well be dug into by a breaker in the future.

 

[bernardgreen]

32 mm duct, sometimes called "civil duct" is stocked by many builders merchants.

Cap the ends to prevent any stones or other object getting into the duct. A couple of small stones can prevent the cable being pulled through

Don't bother with the draw cord when you install the duct. Leave it until you are about to pull in the cable.

Often the cable can be fed into and right through the duct without the need for a draw cord if there are no sharp bends. If you do need a drawcord then a vacuum cleaner can be used to suck a light weight string through the duct