How to get draw cord or wire down underground 25mm flexible conduit

[Spinny]

Had someone installing a new mains water pipe. They ended up having to trench it the 25m to the house and managed to break the old lead pipe in the process. As it was being trenched I thought I would get some 25mm flexible conduit down the same trench before they filled it in (to take a future internet fibre cable). Spent quite a while messing about with a drill bit attached to some cord to work the cord down the 25m of flexible conduit and secured it at each end with something to prevent it getting pulled back and lost in the conduit. But god didn't grace everyone with a brain and the trencher buried it then decided to cut the 'spare' off the end releasing the string back down the conduit. Expletives were uttered - just another episode in my cursed 2.5 year attempt to get a modest extension.

 

A fish tape was tried but got stuck a few metres down the ribbed conduit.

An attempt to suck down some string taped to a piece torn off a plastic bag with a Henry vacuum only slowly pulled it a few metres.

I still have the original cord taped to one end but of course the other end is lost, so we thought we would pull this cord out and try the vacuum again, but hell now even the cord is somehow stuck in the conduit and will not pull out.

 

Seems like I am s###### again - any ideas on how to try to get something down the conduit ? Trencher believed cable companies use sort of air gun to fire the cable down ?

[Andehh]

Tried a more powerful hoover? I bought a screw fix shop vac and it sucked through a 35m x 50mn duct without an issue... Even drew the water out.... Plastic bag and draw cord did the job... That or UFH pipe, smooth, stiff and easy to push in....

Edited Sunday at 20:45 by Andehh

[FuerteStu]

String with a couple of knots in the end, hoover, switching it on and off. 

 

Use gravity and the wave effect of increasing and decreasing pressure.. 

 

Usually works. 

 

Replace the string with thicker after you've made it through. 

[Mr Punter]

Sorry but 25mm conduit for a 25m run is a no-no.  Can you get a Cobra type duct rod?

[ProDave]

2 hours ago, Spinny said:

I still have the original cord taped to one end but of course the other end is lost, so we thought we would pull this cord out and try the vacuum again, but hell now even the cord is somehow stuck in the conduit and will not pull out.

There is your answer. the conduit is probably crushed by a stone somewhere and sadly useless.

 

For anyone reading, only use a much larger smooth sided rigid conduit.  50mm absolute minimum.

[Alan Ambrose]

@prodave - any brands or products you recommend?

[ProDave]

I used flexible I think it was 70mm twin wall.  If it is bought as conduit, the inner wall is a lot smoother than the outer corrugated wall, and it comes with a draw cord installed already, but that is usually just a bit of fishing line, so first use that to draw a decent bit of rope through before burying it.

[Russell griffiths]

Do yourself a favour and forget this duct, it’s now useless, get some rigid grey bt duct and use this, it will future proof you for any new installation of fibre, extra bt cables or whatever. 

[Spinny]

Thanks for all responses.

 

Further investigation today by pushing cat 6 cable down the 25mm flexible conduit (bought from Toolstation) shows that cable can travel 6.3m down the conduit from the house end before it meets an obstruction and only 2m down the conduit from the far end. So I presume the conduit must have been crushed (or possibly bent ?) at these points, though the henry vacuum does produce significant suction from one end to the other (!?!).

 

The only good news with this is that 6.3m from the house end is just beyond the concrete slab in front of the house. So in theory digging back down 750mm in that one spot should allow the conduit to be cut and joined to a new piece to travel the rest of the way. I guess this means I can reassemble the qtr landing at the bottom of the staircase, but maybe need to dig the hole first.

[Spinny]

19 hours ago, Mr Punter said:

Sorry but 25mm conduit for a 25m run is a no-no.  Can you get a Cobra type duct rod?

The trencher had one but it wouldn't pass far down either end - didn't seem as flexible as the cat 6 cable.

[Russell griffiths]

If you bought this duct from toolstation then it is completely the wrong thing for using underground, this stuff is what you use for inside the house for protecting cables from chafing. 
do yourself a favour and stop pursuing the idea of pulling a fibre cable through it. 
replace it and ask for advice on here in future, DO NOT rely on trades on site giving you the correct advice, you will be amazed at the poor knowledge of a lot of them you will come across. 

[Spinny]

Thanks Russell.

It was all a last minute thing as the water pipe was supposed to be moled down the driveway, but they couldn't do it as the mole just kept hitting rocks in the ground, so had to come back next day with a digger to trench it. I woke up at 5am thinking, hey I could use that trench to conduit a future fibre broadband cable under the driveway and directly into the side of the house where my network stuff lives. So when the workman returned I went hotfoot to buy something as they were already well behind on the job and eager to get finished.

 

They needed to get the job all done, so have immediately laid new patches of concrete where they had to cut through. I might get a second chance to do something as and when I replace the concrete pad.

 

I suppose another option might be digging the hole 3m outside to get back to the conduit, then attach some new conduit to it of the same OD and then using the existing conduit to pull the new conduit through the same hole, but could be dodgy, and where would I find a 25mm OD underground conduit. The one I used I see now is IP54 rated - presumably would take many years to degrade in the ground though ?

[Iceverge]

Plain string with nothing tied to it is often fine to get pulled through a duct by a vacuum. 

 

Your situation sounds unfortunate but not to worry, we're all learning and in the grand scheme of things, it won't be a major life regret. 

 

The plan to dig, add an accessible junction box and run a bigger duct is probably the best options at this stage. 

 

This stuff isn't that dear. 

 

 

[Andehh]

Likely an S bend even if slightly shallow... Can add significantly to the force required to force past it.

 

If a strong hoover, and or blowing down one end with another hoover fails to pass string... It's been crushed!

[Nickfromwales]

I used 6lb fishing line with a tuft of rockwool and pulled that with a Henry. Shot off 100m of it so fast I nearly lost the end.