Sometimes when you need to replace or install an electrical wire or cable, the only method you can use is to snake it through an electrical conduit. But this is rarely as simple as merely pushing a cable. There are techniques and special tools you will need to use.
Depending on the conduit's length, how stiff it is, and how many curves and corners are in it, you will have four optional methods of pulling new wire or cable through the conduit.
Method 1 - Examine Your Conduit
Inspect your conduit from the near end to the far end to determine its length. If the conduit is longer than your fish tape, and if you can use an existing wire or cable in the conduit as a pull string, you'll be left with virtually no other alternative but to use this pull tape method to bring your wire through the conduit.
Method 2 - Use an Existing Pull Wire or String
To use an existing pull wire, first be sure the wire is free and unconnected at the end of the conduit closest to you. Take your box of cable to the far end of the conduit. There, if the pull wire is connected to anything, you will need to free it. Make a loop small enough that it will easily fit into the conduit, then secure the loop by wrapping the free end to the wire strand with tape.
Method 3 - Pull the Pull Wire Through the Conduit
Feed the end of the wire or cable through the loop you made in the pull wire. Make a loop in the feed cable the same size as the one in the pull wire. Secure the end with tape as you did with the pull wire. Position your box of wire so that it will freely leave the box and will enter freely into the conduit. Go to the other end of the conduit and tug on the pull wire until the new cable has come out of the end of the conduit.
Step 4 - Use Wire Lubricant
If the cable you're pulling binds up, you will need to apply wire lubricant to it and enlist a helper. Return to the far end of the conduit. Pull back the cable until you can see the loops you made. Apply wire lubricant to the wire surface. Instruct your helper to pull the cable toward him until he sees the loops in the cable. While he pulls, you add lubricant. Your helper may have to use a cable puller when the cable becomes slippery and hard to hold.
Step 5 - Use Your Fish Tape
If the pull wire should break as it is being pulled through the conduit, and if the conduit is no longer than your fish tape, you'll need to insert your fish tape into the conduit and push it until the end appears at the other end of the conduit. Attach your cable to the fish tape loop as you did with the pull wire. Return to the other end of the conduit and pull your fish through the conduit.