Running cable through trusses
Roof and floor trusses (or engineered joists) are made to exacting specifications, and any holes you drill or notches you cut could weaken them significantly and render them out-of-code.
Where possible run cable through the openings in a truss. In some cases it is best to staple cable to the exposed end of a truss, and then protect the cable by attaching a board on either side. If you need to cut into a truss, first consult with your building inspector.
Wiring through metal studs
Metal studs have convenient holes for running pipes and cables. Be sure to install the studs all in the same orientation and cut at the same end so the holes will line up. Insert protective plastic bushings into each hole before running the cable.
Fishing through a solid corner
In some cases corners are framed with no spaces between the studs. To run NM cable through such a corner drill a 1-inch hole from either side; take care to drill each hole level, so they meet in the middle. Poke a fish tape into one hole, and catch it with another fish tape poked into the other hole. Pull the first tape through, and use it to pull the cable.
Wiring finished rooms
You need the patience of a surgeon to run wiring through walls that are finished with drywall or plaster. At times you’ll feel like grabbing a hammer and knocking big holes in the wall to get at that darned cable. But remember that patching and painting walls are tedious and time-consuming tasks, so any steps you can take to minimize wall or ceiling damage will save you work in the long run.
Follow the easiest path
If you have an unfinished attic or a basement, run as much of the cable there as possible. If a basement or attic is finished, run armored cable instead of NM.
Use an electronic stud finder to locate joists and studs that may be in the way. You may be able to move a box a few inches to avoid an obstruction. Wherever possible run cable parallel to studs or joists.
First cut holes for the boxes; then run the cable. Reach into the box holes with your hand, a fish tape, or a long drill bit in order to reach the cable.
If you plan to take power from an existing receptacle for your new service, make sure you will not overload the circuit.
- To run through a basement below, drill a locator hole
Directly below a box from which you want to grab power, remove the base shoe and drill a ¼ inch hole through the floor. Poke a wire through the hole.
- Drill up through the bottom plate
Using the wire as a reference point, drill a 1-inch hole through the middle of the wall’s bottom plate (a 2x4 lying flat on top of the flooring above).
- Hook the cable
Open a knockout hole in the bottom of the box. Strip sheathing from the cable and attach a cable clamp (remove the locknut). Form the wires into a hook. Poke a fish tape or unbent coat hanger down through the knockout hole while a helper pushes the cable up. Hook and pull up.
Running Cable behind a baseboard
Use a flat pry bar to remove baseboard molding. With a drywall saw cut a channel in the drywall at least 1 inch shorter than the baseboard. Drill holes through the centers of the studs and run cable through the holes. Protect holes with nail plates.
Running cable through a wall
If the new box will be more or less directly behind the existing box from which you will grab power, you can avoid wall patching. Cut the hole for the remodel box. Remove the existing receptacle and punch out a knockout in the back or bottom of its box. Run one fish tape through the existing box and one through the new hole. Hook them together. Pull the tape back through the hole, and you’re ready to pull cable from the hole to the box.
Running cable around a door
If you have no access above or below, this may be your only option. But check to see if this is OK with local codes. Remove casing form around a door and snake cable around. You may be able to slip the cable between the jamb and the stud. Or drill a hole and run the cable in the cavity on the other side of the stud.
Wiring finished rooms
If the attic isn’t used for storage, you may be allowed to lay cable on top of the joist if you install 1x4 strips on either side of the cable.
Running cable up, over, and down
If the attic is accessible, drill a hole through the top plate. Run cable down through it to the hole for the new box directly below. Drill holes and run cable through the joists, over to the spot directly above the existing box from which you want to run power. Strip sheathing from the cable, install a cable clamp (without a locknut), and form the wires into a hook. Punch out a knockout hole and run a fish tape up the wall. Jiggle and slide the tape back and forth until it goes through the hole in the ceiling plate. Have a helper hook the cable to the tape and pull it into the box.
Where the ceiling and wall meet
When there is no access from above or below, cut notches in the drywall or plaster, like this. Drill a 1-inch hole up through the center of the top plate. Bend the cable, poke it up through the hole, and grab it from the other side.
Fishing from the attic
To run cable up into the attic, first drill a locator hole up through the ceiling. Poke a wire up into the hole. The wire may need to extend a foot or so upward to rise above attic insulation. Go into the attic and find the wire. Near the wire drill a hole through the center of the wall’s top plate. You can now run cable up or down through the wall.
Using a Fishing bit
This tool is usually worth its cost because it reduces the number of holes you will need to cut and patch. It has three parts: a long, flexible bit, a guide tool, and a wire grabber that hooks to the end of the bit. First, drill the hole with the flexible bit. Use the grabber to position the bit; it may help to have a flashlight to make sure you are, for instance, drilling through the center of a base plate. Once the hole is drilled, leave the bit in place; don’t pull it back out. At the other end slip the wire grabber onto the cable to be pulled; it has a mesh attachment that quickly and securely grips the cable. Hook the grabber’s hook onto the hole in the end of the bit, and pull the bit back to fish the wire.
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