DO-IT-YOURSELF : Upgrade an Electrical System by ‘Fishing’ Cable

Have you wondered how you might add a switch, light or receptacle to your home with all those finished walls, ceiling and floors concealing the wiring?

Take heart. With a little careful measuring and a complement of luck, you can easily “fish” cable through ceiling and wall cavities, causing little drywall damage.

In many cases, all you will need to fish electrical wire are a cut-in box, sheathed cable, a screwdriver, utility knife and drywall. In some cases, a length of sash chain will come in handy.

For a short run, a piece of coat-hanger wire will serve as a fish tape. For longer reaches, a factory-made fish tape will save you hours of frustration.It’s a thin coiled steel ribbon with a hook on one end.

Some circuits are easy to expand. If you want to add something to an interior wall, check the wall’s back first. In many cases, you can pull power from another receptacle on the wall’s other side. Start by measuring carefully from a common feature on the wall, such as a door. The existing receptacle box will be mounted on a stud. The new box, known as a cut-in box, will not be mounted on a stud.

To determine where to put the cut-in box, poke a putty knife between the outside of the receptacle box and the edge of the drywall. Do this on both sides of the box. The putty knife will go in up to the stud on one side, but on the other it will not hit the stud. This is the side where you install the cut-in box.

On the other side of the wall, mark and cut the opening for the cut-in box a few inches from the existing box. Run wire from the existing box to the opening. Push the wires through the cut-in box and install the box in its opening.

Now install the receptacle in the box, and check that the receptacle is working properly before installing the cover plate.

When extending cable along a wall, in most cases, you will have to run cable from the basement or attic. Which way you run the cable depends on which is unfinished. If you work in the attic, you’ll need to move the insulation aside to find the top of the walls through which you will bore holes to run cable. The wall will run parallel to the ceiling joists or perpendicular to them. If it runs parallel to the joists, look for a drywall nailer (two 2-by-4’s or one 2-by-8) that appears to lie on top of the drywall. A wall perpendicular to the joists is evident by the horizontal 2-by-4 that forms the top of the wall.

After measuring from a reference point, bore one hole to tap into the circuit and another to run the cable. Next, lower an eight-foot-long sash chain into the stud space from above. Secure the chain with a pair of locking pliers.

Poke the fish tape through the box opening (the one you are pulling power from) and snag the dangling chain. Pull the chain into the box, and attach the new cable to it. Pull both into the attic. From the attic, feed the cable into the next hole, and push it down to the new opening. Do not lay cable on top of the ceiling joists. If the cable runs across a joist, bore a hole through the joist and run the cable through the hole. If the cable runs parallel to a joist, staple the cable to the joist’s side.

When working from the basement, instead of using a chain to gain access to the existing box, push the fish tape into the stud space from the basement and snag it through the box with a coat hanger. Then use the fish tape to pull the cable through the box and into the basement.