Power to garden shed

[Craig Wilson]

I've looked around on here and have seen a lot of chat about this issue, but nothing that answers my specific question.

I'm not an electrician, so rest assured (when the time is right) I will be calling one in. My question is this:

Would it be acceptable to, rather than dig a trench to bury SWA cable, build a single course of breeze blocks about 6 inches away from the fence line, such that they protrude above ground level by only 2 or 3 inches, then use this as a base to clip 6mm SWA cable to?

The breeze blocks would be set in the middle of a gravel border with no shrubbery or plants so that the cable routing will always be visible.

I know the electrician would need to be consulted before I do anything, I'm a competent electrical and electronics engineer and would like to do as much as I can such that the electrician could come in, supply and fit MCU/RCD, check wiring, and connect up.

I'm months away from actually doing anything, and the reason I'm asking here first is to get an idea of what costs I can save before I call anyone in for a quote.

My idea would be to fit a new CU in the shed, install wiring for one wall socket (with the intention of adding maybe 5 or 6 more at a later date), and the wiring for one or two lights). The wiring would only be run to the new CU and not connected (waiting for the electrician to connect up).
Similarly, the SWA run from the new CU, out the shed and clipped to the 'shallow' wall. Then at the house the SWA would be clipped to the external wall upwards to a height close to the ceiling height in the kitchen. A hole drilled at an upwards angle into the property and the SWA fed through. Here would be a metal(?) junction box where the SWA would terminate and connect to 6mm T+E flex which would be run at ceiling height in plastic trunking, joining some other mains cables to run directly to the existing CU in the house. Again, at the existing CU in the house the cable would be left coiled ready for the electrician to connect.

Total length from new CU to existing CU would be no more than 20 metres.

My aim would be for the electrician to come along, inspect the cable run, connect at shed, junction box, and existing CU.

I realise that all of this would need to be discussed with the electrician beforehand, this is a theoretical exercise whilst I'm planning my new shed

 

[Octopus]

My aim would be for the electrician to come along, inspect the cable run, connect at shed, junction box, and existing CU.

I realise that all of this would need to be discussed with the electrician beforehand, this is a theoretical exercise whilst I'm planning my new shed

Opinions will vary on this but only the spark signing the installation off can say what they will and what they won't allow you to do.

If its me you called - sure you can dig the trench, and refill it after I've laid in the cable.

Its that simple.

 

[Richard Burns]

A cable fixed onto a surface is an acceptable means of installation, it should be ensured that the cable does not become covered over as it is critical that the the run can be seen.
You would need to engage an electrician in advance to ensure he was prepared to accept the rest of your proposals.

 

[Wes1000]

Is there any reason not to trench it in?
It sounds like more work to dig a footing and lay a wall than to just dig the trench deeper and put the cable in. Just don’t fill it in until the electrician has seen it (check he is happy with that first though.)

 

[Spoon]

Where about in the UK are you. I ask because adding a new circuit is Part P notifiable.

 

[johnduffell]

You could get some galvanised cable tray, the unistrut or whatever, and run it along 6 inches off the ground by the fence off short posts. As long as it's classed as a permanent structure and unlikely to be damaged it's fine.
Some people class concrete fence posts as good enough.

 

[Spoon]

Just out of curiosity, why are you wanting to get the parts? Why not get the electrician to get them, they will probably get them cheaper than you. Unless you are getting cheap rubbish parts. Also I would think that if you make the electrician use the parts you bought then the warranty for the parts are on you and not the electrician.

 

[martinh89]

A trench is always a better option, dug at 450mm with the base sanded with smooth sand and any sharp rocks removed and then an additional 50mm sand above the cable and marker tape for its entire run... I'd also take pictures of the install to show the electrician the condition you left the buried cable in.... Also is 6mm acceptable? What's the expected load? What's the distance from the house c/u to the shed? I would probably consult an electrician to begin with

 

[marconi]

I understand why you want to economise on this installation by doing as much as you can yourself. One needs to be mindful though that there is higher end value to having the installation done completely by a qualified electrician than as a joint venture; this value being to your insurer, you as the owner if ever you come to sell up and to whoever buys from you. In my view this value outweighs any economy in cost to you or the cost of employing an electrician to supply and do the installation. And I say this as a Chartered Electrical Engineer who employs an electrician to do any work me. Just a perspective for you to mull over. Perhaps apply your engineering skill in writing down a clear specification of what you want done - that is what I do.

 

[Craig Wilson]

Is there any reason not to trench it in?
It sounds like more work to dig a footing and lay a wall than to just dig the trench deeper and put the cable in. Just don’t fill it in until the electrician has seen it (check he is happy with that first though.)

I guess it isn't much more work to trench it in.

Where about in the UK are you. I ask because adding a new circuit is Part P notifiable.

As I mentioned, I will be using a qualified electrician. I'm just getting a feel for my options before calling him in. So no 'new' circuit would be added until the electrician comes, and then I presume he would handle the notifications?

Just out of curiosity, why are you wanting to get the parts? Why not get the electrician to get them, they will probably get them cheaper than you. Unless you are getting cheap rubbish parts. Also I would think that if you make the electrician use the parts you bought then the warranty for the parts are on you and not the electrician.

I see, probably would be best to have the electrician supply the parts. Just the engineer in me wants to do as much as possible. I guess the cost difference would be negligible.

A trench is always a better option, dug at 450mm with the base sanded with smooth sand and any sharp rocks removed and then an additional 50mm sand above the cable and marker tape for its entire run... I'd also take pictures of the install to show the electrician the condition you left the buried cable in.... Also is 6mm acceptable? What's the expected load? What's the distance from the house c/u to the shed? I would probably consult an electrician to begin with

I did mention that none of this would be done without prior discussion with an electrician. I'm just trying to get a feel for how much I can do (after an initial consultation and quote from an electrician, but before he comes to do any work) and whether it is actually worth doing any of it myself, or letting him/her do it all.

As I've said, this is months down the road, the shed isn't even there yet. I'm not an electrician and don't move in any circles that allow me to get any advice without actually calling in an electrician for a quote....but don't want to do that until I'm ready for it.

 

[Spoon]

So no 'new' circuit would be added until the electrician comes, and then I presume he would handle the notifications?

This needs confirming with the electrician and make sure it's on the quote for who is responsible for this.

I did mention that none of this would be done without prior discussion with an electrician. I'm just trying to get a feel for how much I can do (after an initial consultation and quote from an electrician, but before he comes to do any work) and whether it is actually worth doing any of it myself, or letting him/her do it all.

Get a few quote done about 3 to 4 weeks before you want the word doing. Some may be booked up for that long. Also gives you plenty of time for digging a trench, if that is the way you go.
Seeing that you are an engineer then I shouldn't have to say that if you are digging the trench then you do it to the depth of 600mm all along the trench and not cheat..

 

[Craig Wilson]

This needs confirming with the electrician and make sure it's on the quote for who is responsible for this.



Get a few quote done about 3 to 4 weeks before you want the word doing. Some may be booked up for that long. Also gives you plenty of time for digging a trench, if that is the way you go.
Seeing that you are an engineer then I shouldn't have to say that if you are digging the trench then you do it to the depth of 600mm all along the trench and not cheat..

Good advice, thanks!

 

[Intoelectrics]

Good advice, thanks!

Nice to see someone asking sensible questions and actually taking the sound advice offered!
Hey if the trench is a pain to dig and you have access to get a mini digger in, they can save you a load of time and you can have some fun while you are at it
Get the electrician to check the trench and then the cable as you lay it to make sure he/she is happy with what you do.

 

[HandySparks]

I'd put a duct in the trench. Put it at 600mm down, with warning tape above. Then the electrician can pull in whatever cable he likes and the duct stops the cable being damaged by bricks and stones in the backfill.
50mm Twin Walled Cable Duct - Black - https://www.tlc-direct.co.uk/Products/FXKVR50.html

Also available from builders merchants.

 

[Intoelectrics]

I'd put a duct in the trench. Put it at 600mm down, with warning tape above. Then the electrician can pull in whatever cable he likes and the duct stops the cable being damaged by bricks and stones in the backfill.
50mm Twin Walled Cable Duct - Black - https://www.tlc-direct.co.uk/Products/FXKVR50.html

Also available from builders merchants.

I agree and encourage this form of installation where possible. It makes perfect sense since the cable can be installed any time after the trench has been back filled and also becomes fully serviceable without having to dig up again in the future.