SWA to garden 'workshop' - running in conduit under ground due to water table?

[Del-inquent]

I seem to be asking a lot of questions on conduits recently, so here's another. 

I'm prepping for an electrician to come and run power to the garden workshop - nothing major just for a couple of sockets and lights. He has specced 6mm2 SWA to give redundancy in case I want to add more later.

I knew we had a high water table here, but didn't realise just how high. I dug the first 6ft of trench down to 500mm, stopped for dinner, went back out and it's half full of water, it's not rained in a few days and been very sunny!

I happen to have some 32mm flexi conduit sat here from when Virgin installed their cable to the house. Would it be wise to throw some of it in the trench to run the SWA through, and bring it up either end to above the water level, so the cable is not permanently sat in water? Any bright ideas on plugging the ends of it? Any downsides to doing this, or any other issues I've not considered?

[JohnMo]

Can you not surface run it, instead of underground?

[Del-inquent]

  On 15/05/2024 at 20:41, JohnMo said:

Can you not surface run it, instead of underground?

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Would get in the way of mowing the grass between the house and workshop a little if I surface run it  😁

[Del-inquent]

Any other views on this? I can't see why it should be a bad idea to run the SWA in conduit, but then I've been wrong before, so my wife tells me.

[Mattg4321]

Just bury the swa direct, the water won’t affect it unless it’s damaged. 
 

Lay it in pea shingle/sand etc before backfilling if there’s any chance at all of sharp objects/hardcore. 
 

The flexi conduit will only fill up with water anyway. 

[markc]

Cable on surface or buried without the conduit

[SuperJohnG]

It's SWA it's fine to sit in water. Also run it in duct, so if need be you can add a cable. 

 

I've a shed (I say she'd burs it's a 19m x 6m steel shed) with 10mm2 up to it, plus numerous ducts from my plant room running different cables different places.

[Onoff]

Proper cable duct in pea shingle, cable tape, draw wire left in etc.

 

Do not use blue water pipe or yellow gas pipe to run your cable through like two guys I know have!

[garrymartin]

  On 16/05/2024 at 23:48, SuperJohnG said:

It's SWA it's fine to sit in water.

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Not really, PVC and LSZH SWA aren't designed for the described ground conditions where it's likely to be wet all (or a considerable amount of) the time. You can get special MDPE-coated cables, but they're more difficult to obtain and expensive.

 

  On 17/05/2024 at 07:21, Onoff said:

Proper cable duct in pea shingle, cable tape, draw wire left in etc.

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That's the way to do it. Proper underground cable duct too, not the flexi you have at the moment.

[Alan Ambrose]

This kind of thing?

 

https://store.jdpipes.co.uk/power-ducting/

 

[Onoff]

Proper DNO stuff I used. Cost me a tenner off eBay/Gumtree. Brought it back round the M25 from Esher ratchet strapped to the roof of my then Golf GTi. 

 

It's smoothbore and a heavy bitch of a thing to wrestle with. 

 

No harm, if trenching anyway to run other ducts in, say a blue one for water in the workshop.

 

Edited May 17, 2024 by Onoff

[Del-inquent]

  On 17/05/2024 at 12:09, Onoff said:

Proper DNO stuff I used. Cost me a tenner off eBay/Gumtree. Brought it back round the M25 from Esher ratchet strapped to the roof of my then Golf GTi. 

 

It's smoothbore and a heavy bitch of a thing to wrestle with. 

 

No harm, if trenching anyway to run other ducts in, say a blue one for water in the workshop.

 

 

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Problem I'm having is finding anything that I don't have to spend a fortune on massive lengths of - I only need 5m of the stuff! The conduit I have is twin wall and apparently waterproof. Given the SWA provides the mechanical protection needed (and I've already got sand / pea shingle / tape to to bed it in) is it really necessary to use such ducting just to prevent it sitting in water? 

[garrymartin]

If the conduit you have is rated for underground, you should be good. Otherwise, it's worth checking Facebook Marketplace - someone usually has small lengths left over from a project.

[Onoff]

  On 17/05/2024 at 12:57, Del-inquent said:

Problem I'm having is finding anything that I don't have to spend a fortune on massive lengths of - I only need 5m of the stuff! The conduit I have is twin wall and apparently waterproof. Given the SWA provides the mechanical protection needed (and I've already got sand / pea shingle / tape to to bed it in) is it really necessary to use such ducting just to prevent it sitting in water? 

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Glue some 3" drainpipe together with solvent weld. Makes a lovely duct. Covered in pea shingle it won't go anywhere. PM me your address and I'll send you a few metres of cable tape to put just under the surface. You can even spiral wrap round the "duct" so there's no doubt should somebody dig it up. The "duct" between my gate pillars is drain pipe. Mind its all then covered in concrete. I've SWA in there then other cables in their own 20mm ducts within the 3" pipe.

 

 

 

Edited May 17, 2024 by Onoff

[saveasteading]

  On 17/05/2024 at 12:57, Del-inquent said:

on massive lengths of - I only need 5m 

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TLC will supply any length cut to order.

They aren't nationwide , but surely some other specialist does this too.

[Del-inquent]

  On 17/05/2024 at 14:59, saveasteading said:

TLC will supply any length cut to order.

They aren't nationwide , but surely some other specialist does this too.

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They don't list it cut to size on their website, I'm going there tomorrow for a few other bits so will ask, cheers

 

[Onoff]

Always good to chuck spare conduits to such a shed/workshop. Good for hardwired internet, cctv etc.

 

Duct to my gate motor for instance, SWA then two 20mm conduits:

 

 

 

[saveasteading]

  On 17/05/2024 at 18:25, Del-inquent said:

cut to size on their website

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[Onoff]

  On 18/05/2024 at 07:37, saveasteading said:

 

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I think it's the duct he wants in a short length. 

[Del-inquent]

Cheers for all the advice, especially the tip about Facebook market place. Managed to find a bloke a few miles down the road with "a little bit" left over for £20... went to pick it up, 45 odd meters left over in fact, so I'll cut my bits off and then sell the rest!