A few questions on laying underground cable?

[HappyHippyDad]

Afternoon all..

I am about to lay approx 30m's of 3 core 2.5mm of SWA (with approx x2 45degree bends and x2 (gentle) 90degree bends where it will protrude, and perhaps 10m of 19 core 2.5mm swa with x2 (gentle) 90 degree bends. These are going in separate trenches.

I realise there is no requirement to put them in conduit but I'd like to just in case they ever need replacing or perhaps an addition needs to be added.

I have a few questions :

1. What size flexible conduit would I need for the above? I do not have the size (diameter) of the cable to hand.. sorry!

2. Is this going to be a struggle or will it pull through fairly ok (with one person feeding and one at other end)?

3. Is there a type of flexible conduit that is not perforated on the inside which would make things much easier? Or perhaps a type of flexible conduit that someone would recommend? I don’t want to use an expensive one (kopex etc) as this is not to afford mechanical protection it is solely to help with future maintenance or design change.

4. I never seem to see the ends of conduit where they come out of the ground covered, so water can get in and will just stay lying inside the conduit surrounding the cable. Is this a concern? I realise the SWA is waterproof, but I am unsure if it is designed to be constantly immersed in water.

Many thanks..

 

[Leesparkykent]

Most twin walled ducting has a ribbed outer surface and smooth inner surface. There is a certain way to tie a draw rope on to a swa so that when you are pulling it tightens up on itself. Pull in a spare rope with the cable to future proof.

 

[Hellmooth]

50mm ducting would be fine? This will bend ok for the 90's as well! Water shouldn't be an issue?

 

[Hellmooth]

Or 100mm to be on the safe side, 50mm is a bit tight!

 

[Leesparkykent]

What's the 19core for? Twinwall Duct Coils

 

[shanky887614]

if you think you can pull 30m of 19c 2.5 swa with just two people it wont be easy.

we did a 100m run of 19c and that wasnt paticually easy but then we had the drum outside on the ground floor and the cable entered the building on the third

make sure to use a good rope and do you know how to tie it properly? i can get a picture later so you can see if you haven't done it before

 

[HappyHippyDad]

Most twin walled ducting has a ribbed outer surface and smooth inner surface. There is a certain way to tie a draw rope on to a swa so that when you are pulling it tightens up on itself. Pull in a spare rope with the cable to future proof.

Thanks for the 1st bit Lee, i'll google it.

I'm happy with the way to tie the rope on so that it tightens up as you pull, thanks though. Will definitely be adding a spare!

if you think you can pull 30m of 19c 2.5 swa with just two people it wont be easy.

we did a 100m run of 19c and that wasnt paticually easy but then we had the drum outside on the ground floor and the cable entered the building on the third

make sure to use a good rope and do you know how to tie it properly? i can get a picture later so you can see if you haven't done it before

Luckily It's only 10m of 19core shanky! Happy with the way to tie it thanks, It was more the size and type of conduit I was thinking about.

 

[HappyHippyDad]

What's the 19core for? Twinwall Duct Coils

I like that link Lee.. cheers! It doesn't show any pictures of the inner lining though, just want to be sure that it's smooth?

 

[Leesparkykent]

I like that link Lee.. cheers! It doesn't show any pictures of the inner lining though, just want to be sure that it's smooth?

Black Twinwall Duct x 50m coil | Ducting | Drainage Online

 

[davesparks]

I'm happy with the way to tie the rope on so that it tightens up as you pull, thanks though. Will definitely be adding a spare!

ut.

The rope shouldn't be tightening as you pull, you should either be forming a pulling loop from the armour or using a sock. Tyeing a rope to the outer sheath of a cable can damage the sheath by stretching it.

Not that you need a rope for ten metres, you will be able to push the cable through that!

 

[shanky887614]

The rope shouldn't be tightening as you pull, you should either be forming a pulling loop from the armour or using a sock. Tyeing a rope to the outer sheath of a cable can damage the sheath by stretching it.

Not that you need a rope for ten metres, you will be able to push the cable through that!

pulling it with anything can stretch it, even using a sock.

 

[davesparks]

pulling it with anything can stretch it, even using a sock.

A sock is better than a knotted rope, and a pulling loop is better than that.
The best thing is obviously an open trench, rollers and a small army.
But I don't think this is going to be long enough distances to even worry about pulling, it's short enough that the cable should just push down there

 

[uksparks]

what do you need 19 cores for? sounds a hell of a lot....

 

[Leesparkykent]

Afternoon all..

1. What size flexible conduit would I need for the above? I do not have the size (diameter) of the cable to hand..sorry!

19 Core 2.5mm LSZH SWA Cable| MeteorElectrical.com

As a guide these are saying the Nominal overall diameter is 26.6mm

 

[davesparks]

what do you need 19 cores for? sounds a hell of a lot....

A company I subbed to last year supplied 19core 2.5 to feed socapex outlets (18 pin connector used for 6x single phase circuits in stage lighting) which was a bit daft when it only needed 12core 1.5, the cable tray was under some stress with the extra weight! (Not my design, I was strictly labour only on that)

 

[davesparks]

19 Core 2.5mm LSZH SWA Cable| MeteorElectrical.com

As a guide these are saying the Nominal overall diameter is 26.6mm

With the added advantage that it's a lot more flexible than a 3/4 core of equivalent diameter.

 

[DPG]

The rope shouldn't be tightening as you pull, you should either be forming a pulling loop from the armour or using a sock. Tyeing a rope to the outer sheath of a cable can damage the sheath by stretching it.

Not that you need a rope for ten metres, you will be able to push the cable through that!

Why would a rope tied round the outside stretch the sheath any more than a sock? Daz

 

[davesparks]

Why would a rope tied round the outside stretch the sheath any more than a sock? Daz

I've never worked that out, but all the advice from cable makers etc I've read says that a pulling loop formed by the armouring or a sock is preferred to tieing a rope to it.

I've got a PDF on the subject somewhere, but I can't find it at the moment

 

[shanky887614]

I've never worked that out, but all the advice from cable makers etc I've read says that a pulling loop formed by the armouring or a sock is preferred to tieing a rope to it.

I've got a PDF on the subject somewhere, but I can't find it at the moment

thats only because a lot of people struggle to tie them properly

 

[Andy78]

I can't imagine that a lashed on rope is going to pull the sheath any more than a wire sock. I have seen the "foreskin effect" with both pulling methods.
It's got to be a big heavy lump though to happen at all. Hardly likely with the cable size and length in this thread.

 

[7029 dave]

30meters sock? give over, that is no distance.
that size cable.

 

[Andy78]

exactly

 

[HappyHippyDad]

19 Core 2.5mm LSZH SWA Cable| MeteorElectrical.com

As a guide these are saying the Nominal overall diameter is 26.6mm

So based on 26.6mm diameter for the cable would you say the 60mm diameter conduit is ok, or would you go bigger?

Also the 3 core 2.5mm is 13.8mm outer diameter.. Just want to get an idea of what size conduit would be used (this would be a 30m run with the bends as stated in the OP)?

 

[Hellmooth]

Personally I'd go for the 90mm with 75mm internal, but it's a fair bit more price wise, the 63mm is a 50mm internal, would be tight but still space!

 

[Marvo]

If there's more than two bends in the run you're unlikely to be able to pull the cable through a duct for any distance. We just use LDPE irrigation pipe for cable duct, it's as good as anything else, it comes in long lengths and it's readily available. A 60mm pipe should be fine for a single 25mm cable. I wouldn't run ducts usually if the route can be reopened afterwards ie it's not part of the civils before paving or roadway is laid, it's unnecessary work and expense.

 

[Hellmooth]

Looking at Lees link, the 110mm with 94mm internal is far cheaper, I'd go for that give you plenty room!

 

[PEG]

Dave is correct,regarding pulling methods,although on short pulls,such as described,a sleeved icicle hitch would be fine. Some lads have done this for years,with nothing more technical than exposing 12" of armouring,and folding it back,to form a loop,this is then whipped secure,and tied to the reeving cord. Not ideal,but that's what they do...

In relation to pulling a draw cord through,at the same time,beware ANY turning of the cable being installed,will put a "wrap" around it,and future pulls will be problematic,to say the least.

This had occurred on a job i was called to,where a set of lads had started to pull a second cable through a duct,using a politely left,draw rope,and the new cable got a boa grip on the original...It would not retreat,and their subsequent hauling attempts,caused the original cable to be pulled,also,thus proof loading its' glanding,and moving it to twenty five to...all still live too :dizzy2:

 

[shanky887614]

Dave is correct,regarding pulling methods,although on short pulls,such as described,a sleeved icicle hitch would be fine. Some lads have done this for years,with nothing more technical than exposing 12" of armouring,and folding it back,to form a loop,this is then whipped secure,and tied to the reeving cord. Not ideal,but that's what they do...

In relation to pulling a draw cord through,at the same time,beware ANY turning of the cable being installed,will put a "wrap" around it,and future pulls will be problematic,to say the least.

This had occurred on a job i was called to,where a set of lads had started to pull a second cable through a duct,using a politely left,draw rope,and the new cable got a boa grip on the original...It would not retreat,and their subsequent hauling attempts,caused the original cable to be pulled,also,thus proof loading its' glanding,and moving it to twenty five to...all still live too :dizzy2:

your better off using a draw wire once and using a cobra to feed a new one in after if there is enough room