Pulling of Cable

[alexi]

Hi All,

I have been instructed to do some pulling calculation for a cable inside some duct. I was told to do pulls from succesive pulling and feeding manholes rather than pulling from one end to another and by passing manholes.

So, let us assume that the scenario:
1- All the cable is in the drum and is pulled towards the first manhole, then I think i have to pull in outside and put it in an "8" position keeping in mind the minimum radius. I think I should take into consderation the cable drum

2- Then I have to pull the cable in the "8" shape towards the next manhole. In this scenario I think I should take the remaining cable only.

Now, how can do the pull calculation to prove the tension do not exceed the maximum pull tension value of the cable [This is my criteria here right or I should check the one for the conductors? ]

What formula should I use to incorporate the small change in elevation and the small bends in the ducts.
Is there any free software that I can use?
Thank you

 

[iwire]

Some info

http://ecmweb.com/content/simple-calculations-cable-pulling

Some more info with calculator.

http://www.electrician2.com/calculators/ductwirepull.htm

 

[bob]

Each pull is separate. The first pull is from the reel to the 1st MH. The second pull is from the 1st MH to the 2nd MH.
The ones I have seen has the cable pulled and placed outside of the 1st MH. This cable is then fed into the conduit
at the 1st MH and pulled to the 2nd MD. You install enough cable so you can loop the cable in MH1. This is done in place of a splice.

 

[kingpb]

You can pull through manholes, nothing wrong with it as long as the pulling tensions are not exceeded.

 

[alexi]

Thank you all,
Now the process is clearer. Iwire, I have used the first link and it shows simple to understand equations, thank you. Wouldn't it be hard to pull the cable outside and then try to put it in the "8" position and then pulling it afterwards to Manhole 2? All the sand stuck on the cable plus it the cable remaining is 150 meters long.
Btw, is there any user friendly software to do the pull calculation?

 

[Tony S]

For once something I?m comfortable with on here. As a Brit and I?m struggling with some of your terminology.

Please don?t pull to the first manhole and figure of eight the cable. The simple reason is the end you need to lead in to the next section of duct is now at the bottom of the pile. If you must pull it in sections loop the cable or zig zag it on the ground. This way you shouldn?t introduce twists or if you?re pulling an armoured cable it will stop ?bird caging? the armours which can burst the outer serving and damage the inner cores.

The funny thing is, I have just been asked about the same scenario on a UK site.

 

[GoldDigger]

...If you must pull it in sections loop the cable or zig zag it on the ground. This way you shouldn?t introduce twists ....

You can also lay the cable out in stacked circular loops without introducing twists. The technique is well known to stagehands and audio technicians.

 

[Tony S]

You can also lay the cable out in stacked circular loops without introducing twists. The technique is well known to stagehands and audio technicians.

I know the technique very well, great for losing excess cable. For cable pulling how do you pull the free end from under the pile so you can continue the run?

 

[GoldDigger]

You just turn the pile over, of course.
No different from the problem you would have with a figure eight or putting it on a spool.

Tapatalk!

 

[Tony S]

I suppose it would help if we knew the size of the cable. Considering pulling calculations are requested I would guess it?s not small. To great a pull and the cable will stretch, one of the reasons a powered cable winch will have a torque limiter.

Rather you than me turning a substantial figure of eight pile over. Added to which, in turning the cable you will introduce a 180? twist in to the cable. I?ve overseen the installation of 100?s of miles of cable so I?m not exactly a novice.

There?s obviously a big difference in what I in the UK would find acceptable and your view of acceptable. My prime concern is to protect the cable from damage.

 

[Smart $]

Figure eight is essentially a condensed a zig zag but the weight of the top loops increase the potential to exceed the minimum bending radius if the pile is not flipped...and even when flipped the conductor should be lifted from the pile while serving, not pulled from the side.

Regarding the 180 degree twist, it is only damaging if done within a short section relative to size and type of conductor. Conductors can easily twist 180 degrees inside a raceway, so that has to be a characteristic of its design. Raceway routing as well as using a twisted rather than braided pull line will influence conductor twisting. Circular stacking definitely twists the conductors unless you roll each stack as it is made... and you also have to unroll each stack when served to the next section pull.

The only reason for even laying out a pull on the ground is a shortage of equipment and manpower. The best way to do sectional pulls is to do all sections concurrently as they progress, and only pulling out enough conductor at each pull point to allow for the rigging and handling.