Pulling SWA through a moled hole.

[gazj82]

Guy from a company we have done a lots of work for over ther years asked me the following today and I didn't really have a good answer since all SWA I have ever had any involvement in installing has always been through a dug trench.

"What are the implications of pulling a SWA through a hole moled through the ground, do we need to duct it first? Will the cable stretch if pulled through directly, i.e with the resistance / friction of earth against its sheath. Is this likely to damage the sheath."

I couldn't really give him a answer I was sure on, hence why I am asking here.

I haven't actually worked out the cable size yet, in fact he hasn't even sent through the Building spec yet for me to determine the size of supply needed.

At a guess on what he has told me for the buildings nature, it will at least be 4 core 25mm pulled through 160m of earth.

What are your thoughts on drag this through the ground with a mole. Would you like to see a duct pulled through first?

I would be worried about a something sharp in the ground binding and damaging the cable, even though according to him they do have some sort of lubricant the mole pulls through first.

Thanks Guys

 

[Engineer54]

Sorry for misleading you Engineer54 - it's hard to remember every detail when posting a new thread. The to and thro questions and answers don't flow like a real life conversation.

I guess I got a little offended by anyone thinking I would even consider using a tractor to instal SWA cable

I've seen tractors and all sorts of other site vehicles/plant used to pull SWA cables into trenches and site ductwork!! It really doesn't work very well at all. Most of that cable needed to be replaced for one reason or the other, usually because of visible stretching and sheath damage. God forbid if i ever saw anything like that being done on any of my projects!! lol!!

 

[Knobhead]

Only ever pulled cable though 6” welded steel pipe. They went under two railway lines and three roads. Four pipes. 3 X 95mm 11KV PILCSWA and a 185mm 3½ core PVCSWA.
I’ll be honest I wasn’t happy about it. But we did use a torque controlled winch and the correct cable stockings.
The bit I was happy about was welding a stud to the end of each pipe and linking them to the MET.

As for PVC serving pulling back, there’s a simple answer. Cut a couple of foot off the pulled end, cap it and let the cable relax for a week. This job took five years to complete, one week was neither here nor there.

 

[Andy78]

Been on a job where we pulled cables in with a scissor lifter before. It was over ground, not through ducts/tunnels however and was helped along with regular cable rollers/shoulders. Worked out fine as we took it at a very steady pace. Really took the work out of moving the weight.

 

[Engineer54]

Only ever pulled cable though 6” welded steel pipe. They went under two railway lines and three roads. Four pipes. 3 X 95mm 11KV PILCSWA and a 185mm 3½ core PVCSWA.
I’ll be honest I wasn’t happy about it. But we did use a torque controlled winch and the correct cable stockings.
The bit I was happy about was welding a stud to the end of each pipe and linking them to the MET.

As for PVC serving pulling back, there’s a simple answer. Cut a couple of foot off the pulled end, cap it and let the cable relax for a week. This job took five years to complete, one week was neither here nor there.

That's basically the only safe way to pull cables through longish duct runs, the correct cable socking for the cable being pulled, along with ample cable rollers/wheels is an absolute must!!. The torque control on the cable pulling winch is set to data given by the cable manufacturer. The torque control acts like a clutch, which will slip the winch drive out as it approaches the dialed in limit(s).

 

[elliot123]

When pulling in cables what would be the best way to attach draw wires to SWA? Only had to do this once threw a 60metre ducting with 25mm 3core and we just drilled a hole threw the cable and threaded the rope threw it…is there any other ways ?

 

[snowhead]

The best people to speak to would be the "Molers"

A. To see if they are prepared to risk moling in previously bombed ground, with or without the customer paying for damage to the mole
B. To get thier opinion of pulling such a cable with the mole and have they have done it before.

 

[gazj82]

The best people to speak to would be the "Molers"

A. To see if they are prepared to risk moling in previously bombed ground, with or without the customer paying for damage to the mole
B. To get thier opinion of pulling such a cable with the mole and have they have done it before.

He is going to ask the "molers". He just wanted my opinion, and I wanted yours

 

[Engineer54]

When pulling in cables what would be the best way to attach draw wires to SWA? Only had to do this once threw a 60metre ducting with 25mm 3core and we just drilled a hole threw the cable and threaded the rope threw it…is there any other ways ?

Exactly what were talking about, ....There are many way's to attach a pull wire to a SWA cable and the like. Most of them will cause damage to the cable being pulled, depending on how much stress is applied to the pulled cable. The correct method is by use of a correctly sized cable socking that will tightly grip the pulled cable over about a metre of the cable length.

 

[benji]

pulled long hv cables used long stocking then drilled 2 holes through cable sock and cable (at different angles )then bolted sock to cable and taped up well

 

[Andy78]

As said Elliot, use a cable sock. If its put on right it won't pull off. The more pressure you exert it just gets tighter.
If you don't have a sock, a series of loops and half hitches works very well.

 

[Engineer54]

pulled long hv cables used long stocking then drilled 2 holes through cable sock and cable (at different angles )then bolted sock to cable and taped up well

Why the hell would you need to bolt a cable sock to a cable?? Really, the mind Boggles!!

 

[benji]

it came from a rep. from cable manufacturers it also helps with the stress/stretching of cable ,also recommended in australia after cable fell 16 floors in a riser (is your mind still boggling)

 

[Engineer54]

it came from a rep. from cable manufacturers it also helps with the stress/stretching of cable ,also recommended in australia after cable fell 16 floors in a riser (is your mind still boggling)

It will do absolutely Nothing to alleviate stretching or reduce stress of a cable....

I'd like to see that recommendation, a cable sock actually works better the more weight you are pulling on. So either the sock wasn't of the correct size for the cable being lifted, or was of the wrong grade of steel for the weight of cable...

I have never seen at any time or circumstance the need to bolt a cable socking to the cable. Kind of defeats the whole purpose of the cable sock too, when you think about it!!!

So Yes, the minds still boggling!!

 

[benji]

SAFETY ZONE
ALERT
3 March 2010
www.cfmeu.asn.au
CABLE PULL FAILURE
Background
Recently on a construction site in Perth’s CBD the electrical contractor was in the
process of pulling a 50mm Diameter fire rated cable from basement 2 to level 21.
The pulling “sock” which was attached to
the end of the cable slipped off, causing the
cable to drop from level 16. It started to spool on the ground floor and basement 1.
All entry points to the riser had been bunted
off and signage displayed stating activity
occurring.
No one was injured from the incident.
Cable was in no state to be used and was recycled.
Root Cause
The cable’s orange shield had stripped away
from where the sock had been placed
on the end of the cable. Refer to photos.
Corrective action
Cables now are required to be spliced and shackled to pull line, in addition to pulling
sock bolted through cable. Ref photos.
View of orange shield stripped away from 50mm fire rated cable.
View of corrective actions, shackles atta
ched through cable splice to pull line as
secondary safety control as well as sock bolted through cable

 

[Engineer54]

You wouldn't happen to have the photo's of the ''root cause'' would you.?? Never heard or seen the PVC outer sheath being ''stripped off'' a cable being pulled via a cable sock....