Power to remote garage - conduit and cable and feasibility

[JohnW2]

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.

All true. I was really thinking of those laid in sand or just on blobs of mortar, which is what I am mainly used to, and only an idiot would take a breaker to them!

(or indeed if the patio is concrete)

Interestingly, during our very recent discussion about kitchen floors, I think the consensus was that even T+E without mechanical protection, let alone SWA, would be OK if buried >50mm deep in a concrete floor.

Kind Regards, John

 

[westie101]

The 450mm matches the recommended depth of DNO LV cables, this depth has been the case for many years

600mm matches the recommended depth for HV cables

1000mm is the depth we would lay in farm land.

Though the routes of DNO cables are also recorded and available.

Interestingly I've never seen any advice that the routes of private cables should be recorded in gardens and a copy kept for future reference[/code]

 

[ban-all-sheds]

All true. I was really thinking of those laid in sand or just on blobs of mortar, which is what I am mainly used to, and only an idiot would take a breaker to them!

How rare are idiots, exactly?

 

[Stevos]

All true. I was really thinking of those laid in sand or just on blobs of mortar, which is what I am mainly used to, and only an idiot would take a breaker to them!

How rare are idiots, exactly?

Having just taken up a patio that was bedded on blobs of mortar, I will admit to giving one of the slabs a whack with a 14lb sledge hammer when it wouldn't immediately come up...

Having said that, I was pretty sure there was nothing underneath it but a poured concrete slab, some mud, and a family of mildly concussed woodlice - as I'd already removed the surrounding ones.

 

[JohnW2]

All true. I was really thinking of those laid in sand or just on blobs of mortar, which is what I am mainly used to, and only an idiot would take a breaker to them!

How rare are idiots, exactly?

You know the answer to that as well as I do

However, I wonder if one is really meant to 'foresee' what might happen during destruction of a structure or part of a structure - after all, an unprotected cable (compliantly) buried >50mm deep in a wall might well not stand much chance in that situation. Furthermore, as I said in my last post, cable buried >50mm deep in a concrete floor (to which someone might also take a breaker one day) appears to be acceptable.

Kind Regards, John

 

[Stevos]

So is it generally agreed that 450mm under lawn, patio, and decking, with suitable marking tape should be considered reasonable?

I was worried I might have to go deeper, and wasn't sure if it would be possible with a spade. 450mm sounds difficult, but might be achievable.

I assume I'd want the duct to come out vertically at the walls, with a foot or so spare at each end (to allow trimming as needed), as per my wonky diagram:

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

In terms of refilling the trench, do I need to worry about sand etc around the duct? That would make it a bigger job due to getting piles of sand delivered.

 

[JohnW2]

So is it generally agreed that 450mm under lawn, patio, and decking, with suitable marking tape should be considered reasonable?

Very much so - some would say 'more than reasonable'.

Kind Regards, John

 

[plugwash]

However, I wonder if one is really meant to 'foresee' what might happen during destruction of a structure or part of a structure - after all, an unprotected cable (compliantly) buried >50mm deep in a wall might well not stand much chance in that situation.

I think there is an issue of reasonable expectations.

I would hope that people when demolishing a building that had electrical service or demolishing major parts of said building would realise that there were likely to be cables present which needed to be traced and isolated first.

OTOH I would find the idea of a cable that entered a building and left again without connecting to anything in the building a very dubious one because there would be no real indication to people doing the demolition.

And I would consider the same to apply to the cable under a patio.

 

[JohnW2]

I think there is an issue of reasonable expectations.

There is - and, although opinions will obviously vary, what you go on to say would seem to be pretty reasonable.

And I would consider the same to apply to the cable under a patio.

Fair enough - and, in any event, it's become fairly moot, since the OP had decided to bury his duct 450mm beneath the patio. Mind you, in general the regs allow SWA to be in a 'mechanically vulnerable' place (e.g. shallow buried in a wall, not in a safe zone) - so one might ask why not the same when under a patio.

However, in terms of what you've said about 'reasonable expectations', what is your view about an unprotected cable buried, say, 55mm or so below the surface of a concrete floor?

Kind Regards, John

 

[westie101]

Interestingly at a commercial level the Construction Design & Management Regulations do try to achieve these aims.
Trouble is, as far as I've seen, some of those involved just ain't got it yet!

 

[Stevos]

Does anyone know what the situation is with building / planning control?

Do I need to apply / notify / inform before laying duct, or only when I want to put cable through it?

(Or would the cable installing electrician handle that?)

I'm pretty sure our property search thing didn't show up any existing ducts, cables, pipes etc in the way when we bought the house, but will check again.

 

[bernardgreen]

You do not need planning permission or building control permission to install a duct in a trench. ( if the building was a listed building of in a conservation area some permission may be required )

Be sure to make a photographic record of the process with clear indication of the depth of the trench by a tape measure in the photographs. This will be needed when the cable is installed to prove the duct is sutiable.

When digging the trench be alert for other services. Plans and deeds seldom have all the services marked on them and if they are mentioned the route shown may not be the actual route

 

[ericmark]

One can't protect against all things which may happen in the future at best you use some common sense.

I have seen water and electric supplies hit which were not at 450 but the reason was it was on a hill and the land had been moved around and very likely it was at 450 when laid.

To me where it is likely land is moved around then tiles or tape is very important.

Although when my son hit the power cable with a Rotavator there was not enough warning for him to have turned it off before hitting cable after yellow tape appeared. When it was re-laid it was put much deeper.

People do want flat and level areas so laying under an already flat level lawn 450 is ample but when surface is undulating one has to allow for that to alter in the future.

 

[Stevos]

People do want flat and level areas so laying under an already flat level lawn 450 is ample but when surface is undulating one has to allow for that to alter in the future.

Good point - and I'm actually planning on levelling out the lawn as part of the same process.

Thanks to all for the advice - I'm almost ready to begin.

A couple more question in terms of ducts:

What's the maximum mm2 / capacity cable I'd be likely to fit in a 40mm (32 internal) , 50mm (40 internal), and 63mm (50 internal) ducts? (I'm not sure what type of earth the house uses, but I assume the duct would have to carry 3 cores)

The cost difference is negligible, but I'd obviously rather not have something that looks like a main sewer pipe emerging next to the house and garage, as it would be in quite an obvious location. On the other hand I don't want to risk it being too narrow for requirements, especially considering the inexpert installation / bending. I guess I could lay two ducts in the same trench...

Also, in terms of sealing the duct ends until they will be used - Is a wedge of foam insulation topped off with a bit of silicone sealant a reasonable idea?

 

[Stevos]

Well I've opted for the 40mm (32mm internal) duct, and plan to try to make the trenches and lay it this weekend. From what I can see, it looks fairly substantial, so I can imagine a fairly thick cable could be run through it (though if it's anything like the stiffness of 10mm T&E - the largest I've personally seen in general DIY stock - I can imagine some difficulty in pulling it...)

I'm still wondering what sort of cable would go through it (in terms of capacity and type), and whether it's worth running two lengths of duct whilst I have the trench dug to future proof it, or whether that would be overkill.

Any thoughts / comments welcome - thanks