The nylon rope inside the conduit is to help you pull cable through the conduit. Usually it is at least twice as long as the conduit itself. Here is how you would pull cable through the conduit:
- Without untying any rope, from the "near" junction box, pull the rope all the way through the conduit. If your piece of rope looks long enough for the length of conduit, skip to step 3.
- Your rope is not long enough. Get a long piece of rope. Untie the rope from the "far" junction box and tie it to your piece of rope. If necessary, tie your new rope to the "far" junction box (this is to prevent the rope from disappearing inside the conduit if it's too short). Go to step 1.
- Tape your cable to the rope, at the point that is nearest from the "near" junction box.
- Push the end of the cable inside the junction box.
- From the "far" junction box, gently pull on the rope. If you feel any resistance, try a few slightly hard tugs. Be careful not to break the rope. If you are unable to pull it further, pull it back from the other end and try again.
- Once you see the end of the cable, pull it out. Untape it from the rope and tie the rope back to the junction box. You are done!
Note that depending on how tight the conduit is, you may be able to run more than one cable at the same time. I suggest running a length or of Cat-5 (6 or 7 is even better) or two.
If you are pulling network cable from a box, you usually do not need an excess length of rope: you simply pull twice the desired length of Cat. 5 through the conduit using the rope, then you tape the rope to the cable so that you can pull back half of the cable, bringing back the rope with you. Do this only for short runs though, otherwise you end up with meters of cable that you will have to carry outside of your box of cable. It's a bit risky though, because if the tape gives way, you lose the rope.
Without a puller rope, you will need a fish tape. The principle is the same, except that the fish tape is made of steel, so it is a bit more rigid. You can push it inside the conduit and it will follow all the bends (to a certain extent).