SWA cable depth

[mg123]

I'm having a new electrical feed to my garage and was looking for some advice on the depth the tench needs to be?
Currently there is an old 2.5mm 3 core feed but I'm moving it up to 6mm 3 core (not doing it myself, I'll leave that to the professional).
I will only be running 2 socket radials and a lighting radial out there so no need for a larger diameter.
However to save a few pounds I'm digging the tench myself hence the question.


Much appreciate any feedback.

 

[RogerS]

Last time I looked it was 600mm. 6mm is a very decent size but does beg the question....how far is it and what might you be pluggin in to those two radials. Chances are you're good to go but ...

 

[mg123]

Last time I looked it was 600mm. 6mm is a very decent size but does beg the question....how far is it and what might you be pluggin in to those two radials. Chances are you're good to go but ...

My garden is a pain, so many bricks and rubble buried out there. Oh well, as for length, it will be approx 20 metres from inside consumer unit to the small garage unit. Highest rated tool is my triton TRA001 router, I believe it's quoted as 2.5 kwatts

 

[Myfordman]

Possibly best to talk to your sparky. He will be signing off the work to state it is compliant with regs and know the minimum depth required and distance from other services as well as the power/length/gauge calculations.

 

[Etaf]

not doing it myself, I'll leave that to the professional).

its ok, to get the guidelines/rules off the forum, BUT as you are getting a Pro , maybe best to ask the professional who is doing the wiring and signing it off for you - they should be signing for the design/installation/test

the last thing you need , having dug a 20m hole 600mm deep, if for he/she to say its not correct for whatever reason

just a thought

 

[BucksDad]

Ask the electrician what depth he wants it for him/her to be happy to sign it off

 

[sams93]

I did exactly this about 18 months ago. My shed is 35m from the house and I ran 6mm SWA. I think I buried it 600mm under the grass, and 100mm under the concrete (which I then re-concreted over). I put the cable in conduit under the concrete in case I ever wanted to run any other wiring under there one day.

I put a small garage consumer unit in the shed with an RCD and run two radials on B16 MCBs and another single socket dedicated for my 12v lighting set up which is on a B6 MCB which came with the unit. The two radials go down either side of the shed, I always debate whether to complete the ring and change it to a single ring. There’s also two outdoor sockets I’ve put in the garden.

At the other end in the house is connected to a B32 breaker in the consumer unit.

I did all the work except the final connection to the consumer unit in the house to save costs, electrician just agreed the plan and checked it all over once I’d done it. Electrician was happy with the depths which we discussed beforehand. I was wondering if he’d want deeper in the concrete but he was happy with the fact that it was obvious where the cable goes in to the concrete and comes out.

I quite enjoyed doing it but the digging of the trench was a bit laborious. I came across some old foundations which were possibly for an outdoor toilet once (it’s an 1880 house), I had to dig under the foundations and pass the cable underneath them which was a chore.

 

[ChaiLatte]

Belt and braces job is to put a bit of 'caution electric cable below' tape on top of it before backfilling.

 

[Daniel2]

Belt and braces job is to put a bit of 'caution electric cable below' tape on top of it before backfilling.

Well, the real correct way to do it, is to dig the trench to 600/700 mm. Lay the cable, in a conduit, at the bottom.
Then back fill 200mm +/- with trenching (silver) sand, then lay the electric (red) warning grill tape, then finish
backfilling with the soil.

 

[mg123]

I did exactly this about 18 months ago. My shed is 35m from the house and I ran 6mm SWA. I think I buried it 600mm under the grass, and 100mm under the concrete (which I then re-concreted over). I put the cable in conduit under the concrete in case I ever wanted to run any other wiring under there one day.

I put a small garage consumer unit in the shed with an RCD and run two radials on B16 MCBs and another single socket dedicated for my 12v lighting set up which is on a B6 MCB which came with the unit. The two radials go down either side of the shed, I always debate whether to complete the ring and change it to a single ring. There’s also two outdoor sockets I’ve put in the garden.

At the other end in the house is connected to a B32 breaker in the consumer unit.

I did all the work except the final connection to the consumer unit in the house to save costs, electrician just agreed the plan and checked it all over once I’d done it. Electrician was happy with the depths which we discussed beforehand. I was wondering if he’d want deeper in the concrete but he was happy with the fact that it was obvious where the cable goes in to the concrete and comes out.

I quite enjoyed doing it but the digging of the trench was a bit laborious. I came across some old foundations which were possibly for an outdoor toilet once (it’s an 1880 house), I had to dig under the foundations and pass the cable underneath them which was a chore.

Great detail thank you, could you tell me what conduit you used?
So far, I think the previous owner built a house in the back garden, no more than 2 inches down and I'm finding more bricks than ever. At least it'll keep me well exercised.

 

[sams93]

Great detail thank you, could you tell me what conduit you used?
So far, I think the previous owner built a house in the back garden, no more than 2 inches down and I'm finding more bricks than ever. At least it'll keep me well exercised.

I can't remember exactly but I think it was 32mm (like this).

 

[Antomakes]

I'm having a new electrical feed to my garage and was looking for some advice on the depth the tench needs to be?
Currently there is an old 2.5mm 3 core feed but I'm moving it up to 6mm 3 core (not doing it myself, I'll leave that to the professional).
I will only be running 2 socket radials and a lighting radial out there so no need for a larger diameter.
However to save a few pounds I'm digging the tench myself hence the question.


Much appreciate any feedback.

It’s SWA it isn’t a regs requirement to bury it. The steel wire armour casing is the reason for this.

 

[Antomakes]

It will need to be protected or buried only where damage is likely to occur by foot or vehicle traffic.

 

[Farm Labourer]

I tend to use 100mm poo-brown underground sewage pipe as conduit if burying at 600mm. I always leave a length of blue polypropylene 10mm rope rope in the conduit with a couple of metres of extra length in the conduit and leave the ends just under the finished surface, so if I want anything else in there at a later date - I don't have to excavate.

 

[John Brown]

It’s SWA it isn’t a regs requirement to bury it. The steel wire armour casing is the reason for this.

That's what my electrician said.
I had other problems, though(already at limit of incoming power), so I went solar. Fairly pleased so far, everything works except staple/nail gun. On the other hand, I don't spend a lot of time out there, and less using power tools.

 

[petah49]

I'm having a new electrical feed to my garage and was looking for some advice on the depth the tench needs to be?
Currently there is an old 2.5mm 3 core feed but I'm moving it up to 6mm 3 core (not doing it myself, I'll leave that to the professional).
I will only be running 2 socket radials and a lighting radial out there so no need for a larger diameter.
However to save a few pounds I'm digging the tench myself hence the question.


Much appreciate any feedback.

Hi there,
I used to work in Utility Engineering contracting for the old SEB & EEB etc. Lv cable was always laid at 450mm (18 inches) deep in footway and unmade ground (600mm or 24 inches) in the carriageway. You should lay the cable in 75mm soft sand bed and surround and position cable marker tape (danger electric cable beneath or similar) 150mm or 6 inches above the cable. If laying beneath hard surfaced places I would install a duct (pipe) should you ever need to replace it.

 

[XTiffy]

I agree with petah49 on depths. I have used 50 or 60mm black cable ducting with additional draw string as mentioned. Then sand and marker tape. This would also enable you to "double-up" on the cable if it was ever needed.
In my photo you can see two of the cable conduits one for electrics and one telephone & Cat 5 cable. These run to the home office cabin in the background. Now that the house build is underway they have been exposed (marker tape gave the digger operator fair warning to their position). These cables will then be re-routed. I would always suggest putting in the conduit as it saves digging anything up later (and there is always a "later"!). Moral of the story do it properly once.

 

[Spectric]

It’s SWA it isn’t a regs requirement to bury it. The steel wire armour casing is the reason for this.

But when the local supplier lays cables to a property they use a plastic duct, maybe just for convenience as the people digging the trench are not the ones laying the cable, they turn up and just feed the cable through and make final terminations.

 

[Antomakes]

But when the local supplier lays cables to a property they use a plastic duct, maybe just for convenience as the people digging the trench are not the ones laying the cable, they turn up and just feed the cable through and make final terminations.

The local supplier (the DNO really) isn’t bound by wiring regs.