Cable duct for under ground SWA

robd · Sep 17, 2018

Afternoon all,

On an extension job, customer wants a cable run to a pond which is 70m from the house, for oxygenation and some lights.

There are quite a bit of groundworks going in including all the drains which will be running downhill to said pond and are being dug currently.

Builders want power to go down whilst all the digging is being done. Question is means of getting down there, usually I'd ask for standard 500mm trench but in this case it will probably go in to the side of drains well below surface. What I had thought is SWA inside Black electric cable polyduct as per link here:

Electric Cable Polyduct 32/37mm Black Smooth Single Wall - 100m | Drainage Superstore® - https://www.drainagesuperstore.co.uk/product/electric-cable-polyduct-3237mm-black-smooth-single-wall-100m.html?gclid=EAIaIQobChMIoKCC_KzC3QIVAvhRCh1uxweOEAkYAiABEgL79PD_BwE

Just wondered a. if anyone had a better idea and b. if you've used the duct before is there somewhere else it can be bought short of phoning round builders merchants.

Thanks in advance.

Midwest · Sep 17, 2018

Give you a bump. Thats a hell of a way to run a swa, no chance of doing it subsequently. Think you might need rigid ducting of some sort with access points.

Pete999 · Sep 17, 2018

robd said:
Afternoon all,

On an extension job, customer wants a cable run to a pond which is 70m from the house, for oxygenation and some lights.

There are quite a bit of groundworks going in including all the drains which will be running downhill to said pond and are being dug currently.

Builders want power to go down whilst all the digging is being done. Question is means of getting down there, usually I'd ask for standard 500mm trench but in this case it will probably go in to the side of drains well below surface. What I had thought is SWA inside Black electric cable polyduct as per link here:

Electric Cable Polyduct 32/37mm Black Smooth Single Wall - 100m | Drainage Superstore® - https://www.drainagesuperstore.co.uk/product/electric-cable-polyduct-3237mm-black-smooth-single-wall-100m.html?gclid=EAIaIQobChMIoKCC_KzC3QIVAvhRCh1uxweOEAkYAiABEgL79PD_BwE

Just wondered a. if anyone had a better idea and b. if you've used the duct before is there somewhere else it can be bought short of phoning round builders merchants.

Thanks in advance.

Some Garden is that.

Strima · Sep 17, 2018

Twin wall cable duct: 50mm x 50m Black Twinwall Electric Cable Duct | Drain Depot - https://www.draindepot.co.uk/50mm-x-50m-black-twinwall-electric-cable-duct.html

Also pull in a couple of draw cords for future use if required.

Seal duct ends with resin pack: Resin Pack 14B - Polyurethane Duct Sealing System - http://www.alh-systems.co.uk/resin-pack-14b-polyurethane-duct-sealing-system

Marvo · Sep 17, 2018

It would be a lot cheaper just to bury SWA direct in the ground alongside the builders piping unless they've specified ducting for some reason.

chris gray · Sep 17, 2018

Tbh the question should be: will the ground workers have a leg to stand on when they find my cable has been laid in their trench before they had chance to lay their pipe work

bigspark17 · Sep 17, 2018

Why the expense of the duct? Buried direct is perfectly acceptable.

Midwest · Sep 18, 2018

bigspark17 said:
Why the expense of the duct? Buried direct is perfectly acceptable.

Not in all conditions, according to some manufacturers;

Electric Cables in Water? Cables Installed in Waterlogged Condition - https://www.whyprysmian.co.uk/underground.html

Pete999 · Sep 18, 2018

chris gray said:
Tbh the question should be: will the ground workers have a leg to stand on when they find my cable has been laid in their trench before they had chance to lay their pipe work

Don't know but you may find your cable in lots of little pieces.

robd · Sep 18, 2018

chris gray said:
Tbh the question should be: will the ground workers have a leg to stand on when they find my cable has been laid in their trench before they had chance to lay their pipe work

Pipe is already in, cable is an afterthought

robd · Sep 18, 2018

bigspark17 said:
Why the expense of the duct? Buried direct is perfectly acceptable.

There's quite a bit of rubble etc in the stuff that's been dug out and will back fill after. I didn't want to run the risk of cable being pierced.

robd · Sep 18, 2018

Marvo said:
It would be a lot cheaper just to bury SWA direct in the ground alongside the builders piping unless they've specified ducting for some reason.

Just wanted to give it a bit more protection, as above. Don't want to dig a 70m trench if it gets damaged, 7m is bad enough.

robd · Sep 18, 2018

Pete999 said:
Some Garden is that.

Pond is only halfway down

Midwest said:
Give you a bump. Thats a hell of a way to run a swa, no chance of doing it subsequently. Think you might need rigid ducting of some sort with access points.

Was going to feed cable through before burying rather than after and not planning on using duct for anything else so isn't access point a bit overkill?

davesparks · Sep 18, 2018

bigspark17 said:
Why the expense of the duct? Buried direct is perfectly acceptable.

If you trust the people burying it to bed it in soft material correctly and not cover it with rubble and other rubbish that could damage the sheath.

robd · Sep 18, 2018

Midwest said:
Not in all conditions, according to some manufacturers;

Electric Cables in Water? Cables Installed in Waterlogged Condition - https://www.whyprysmian.co.uk/underground.html

bigspark17 said:
Why the expense of the duct? Buried direct is perfectly acceptable.

Living where we do the soil is clay, the house comes in the local authority Broads Authority so would expect the ground to be sodden at that depth in the winter, it's a pretty deep trench.

robd · Sep 18, 2018

davesparks said:
If you trust the people burying it to bed it in soft material correctly and not cover it with rubble and other rubbish that could damage the sheath.

This is my main concern.

chris gray · Sep 18, 2018

Make sure it’s smooth sided duct. We’ve just tried pulling a 50mm 4c through a 120mm ribbed duct! Even though it’s flexi duct we’ve had endless problems!!

SJD · Sep 18, 2018

I've used duct from the drainage superstore for SWA, but somewhat larger - I used 50/65 recently, smooth inner wall, ribbed outer. I think 32/37 is maybe a bit small.

Over shorter lengths (15 to 20m) it was actually easier to push the SWA through the duct (6mm/3-core), rather than pull it. I don't think you'd want to try pulling/pushing the SWA through before it is laid.

davesparks · Sep 18, 2018

chris gray said:
Make sure it’s smooth sided duct. We’ve just tried pulling a 50mm 4c through a 120mm ribbed duct! Even though it’s flexi duct we’ve had endless problems!!

Get a ball a little bit larger than the cable and drill a hole through it. Fit the ball over the pulling rope at the point where it joins the cable and tape it up so there’s a smooth surface between the ball amd the cable. The ball should give a nice rounded surface to ride over the ridges in the duct.

robd · Sep 19, 2018

Thanks for all the replies really helpful. Builder was picking up a twin walled 50mm duct today so will call by tomorrow and see what the score is.

Marvo · Sep 20, 2018

A cable pulling sock can also make life a lot easier if you're pulling through ribbed ducting.

robd · Oct 4, 2018

Final update, cable went in a treat down the twin walled duct. Thanks for all your help, very useful and now I know.

Marvo · Oct 4, 2018

Glad you got it in with no issues. Did you pull the 70 meters in one go? What technique did you use?

robd · Oct 9, 2018

Marvo said:
Glad you got it in with no issues. Did you pull the 70 meters in one go? What technique did you use?

I used the get the builder to do it technique as I wasn't there , it was 70m in one go, the duct came with a draw wire built in and was quite a bit wider than the cable so it should have gone through easily I think. Was also a pretty straight run slightly down hill, I didn't ask them how they did it I'm only popping in occasionally as they are doing footings etc but will find out next time.