Overhead Power cable from my house to my barn

I know of no reason why you can't have an overhead cable if you want. There might well be requirements on its height depending on how the land is used (esp. vehicles passing underneath), for that length you may need some intermediate supports (poles) and likely a catenary wire to hang the cable itself off, and would have to be a bit careful in your choice of cable (esp. w.r.t. UV resistance) (T&E outdoors is frowned upon these days) but nothing insurmountable.


Underground is often preferred these days - but I think that's mostly for aesthetic reasons.


If you do bury, 3' down seems a little excessive unless the land is being ploughed - usually it's something closer to half a metre in most circumstances. AFAIK the regs don't specify any particular depth - just something suitable to avoid forseeable disturbance,


   - Andy.

not illegal, in the sense of 'point to the law it breaks please'

We cannot see the route, and there may be a good reason why overhead is tricky, but that is not a legal issue.  A span of 25m unsupported would need a fairly bosky stay wire, think 5 or 6mm stainless steel, depending on the cable weight, and it will impose significant lateral forces on the mounts - it is important to realise that you cannot have a perfectly straight line, as that requires an infinite tension, (think of the drop of a heavily loaded washing line.),. Ideally  the cable forms a graceful catenery curve, over 25m aim for maybe 0.5m droop from the straight line at the mid point. If the building is not up to the side forces involved then the usual solution is poles and guy lines at the ends, which on private property are usually scaff poles planted in cement footings rather than the electricity company style telegraph poles that require most of a tree each.

As above, you want to be high up, say 4,5m or so  if full sized vehicles may go beneath less maybe OK if it is cars only or you have some other feature like an arch that limits heights,  though  if possible a route over a hedge or a ditch is better as that reduces that risk to almost nil (or coming underground for any section that crosses a driveway)

Where cables come indoors they need to loop down first, so that water running on the cable drips off, rather than is channelled indoors.

Most things are possible, you do not need to be limited by your sparks' imagination.

Mike.

Agree that a new overhead cable might be simplest and cheapest, nothing prohibits this, subject to the usual caveats regarding electrical work in general.

If burial is prefered, then in most circumstances this does not need to be 3 feet deep. Simply deep enough to avoid risk of damage.


I would suggest use of cable at least one size larger than is needed at present, in case needs change. You might want to convert the barn into living space one day, subject to planning, or you might wish to charge an electric vehicle.

I think the regs recommend between 400mm & 600mm depth to ensure that any cable is buried beyond normal spade of garden fork depth.

Why not this method? I've done 24 m but in very good clay.

https://www.tracto-technik.co.uk/Products/GRUNDOMAT-Soil-displacement-hammers


Regards


BOD

What about the  aesthetics of overheads and are there or not any planning issues etc with that?

3` is better than 2` but as said it just needs to be of a "sufficient depth"

Thanks guys for all the advice - it's been really helpful and since saying to the electrician that I've done some research and can't see any legal requirement for buried cable, he has changed his view and said an overhead would be OK but he'd prefer to have buried it. 


I can try and up load a picture - but the main issue for me is the downhill gradient and a large step down from the front of the house down to the drive which would mean burying and setting back the cable a long way - but also there is drainage under the drive (I live 1 mile from the village that holds the UK record for daily rainfall - so you can imagine what it can rain like here!) so I was very concerned about digging down and disturbing all of that - 


But again - thank you all for coming back on this - it's been very useful info to have! cheers - JS

You may be able to cheer him up by offering to arrange the mountings and the stay wire ends in advance so all he needs to do is clip and slide along - it may be that the working  at height or the risk of pulling bits off the building is the aspect he is not happy with. (It is not unknown for a  rawl-bolted fitting to remove a couple of bricks off  the top course if the forces are not correctly spread, and he may have been caught out by something like that in the past - some folk tend to forget that mortar is not sticky like glue, but is more of a friction fitting due to the sand and the pressure of the layers above. )


(typical low cost parts. 3mm galv wire  Better alternative is larger dia and as you mention the wet, stainless steel   ) Note that for the working load  is not the weight of cable, but the tension  (3mm wires, the working load is 155kilo, for the 4mm s/s the breaking load is 900kgs and the 6mm 2000kg !! - but working and breaking loads are not the same **....)- and that tension depends on the droop - ( and actually it is a surprisingly complex problem )  however, approximately you can get a safe over estimate by pretending that the weight of the cable is at the midpoint of a triangular droop . So if you take my suggested drop of 0.5m over 12.5 (half metre drop at mid span) you get 2.3 degrees, and tension is tangent of (90degrees minus that >> TAN (87.5 deg) is 23  ) times the down force, (half of the total cable weight as the total weight is  held up from both ends) - so about 10-12  times that cable weight as the tension.

Actually  a 6mm SWA would be ~ 18 kilos of cable and by my  noddy rule comes to 180kg of tension. When done slowly with the right formula, it  is more like 125kg force tension, but  even so would be very near or maybe over the limit for the galvanised 3mm cable with a bit of bad weather.  Hence my suggestion to use something bigger, though the best choice depends on your cable size.


Mike.


Edited to clarify the tangent approximation thing applies to half a cable.

PS

**

edited again to suggest SWL (safe working load) should be no more than perhaps 1/4 or a 1/5 of the MBL (minimum breaking load) depending on how serious versus just annoying  it would be if it ever fell down. If there is ever a credible risk to lives, make that ratio more like 1/10 instead. Unless it is an aircraft, where you get things professionally calculated but with much lower safety margins !!

MAPJ1 ,

good advice as ever.


Have you ever thought of writing a book of tips.


These and the "rule of 16" immediately spring to mind ?

some folk tend to forget that mortar is not sticky like glue

If this Welsh barn is anything like the old outbuildings I worked on in Pembrokeshire, the stones are more likely to be held together with something closer to clay than what we'd think of as mortar. The one I worked on had been re-pointed with cement mortar over the years which disguised the fact, but things could become very loose very quickly when you started drilling into it.


Also beware of gable ends of buildings - the triangular shape (lack of weight above it) makes them surprisingly easy to topple given quite moderate horizontal forces.


   - Andy.