How to Fish Wires Through Walls

Three Parts:Prepping the AreaFishing the WiresTroubleshooting

Fishing wires through a wall can be tedious, but in most cases you only need a couple basic tools. Approach the job patiently and thoroughly, to avoid bogging the project down with wasted drilling or damaged wires.

Part 1
Prepping the Area

  1. 1
    Turn off the power. Shut off the electricity to the circuit you are modifying. Double check with a multimeter at the closest outlet where you plan to connect the wires.[1]
  2. Image titled Fish Wires Through Walls Step 2
    2
    Confirm the space is free. Check for studs at the location where you want the wire to exit. Confirm there are no cross beams or duct work along the path the wire will take (typically straight up to the attic, or straight down to the basement). Ideally, use a stud finder that can tell the difference between studs, pipes, and other obstacles.[2] Failing that, locate studs with magnets, or knock on the wall listening for hollow sounds.
    • If there is any uncertainty, drill a small test hole and explore with a bent wire coat hanger.
    • Avoid locations with another electrical outlet less than two studs away. Stay away from exterior walls, which typically contain braces and insulation.[3]
  3. 3
    Locate the same spot from above or below. Check the attic, basement, and/or crawlspace to confirm you have a clear path to thread the wire. You can often find a 2 x 4 or larger beam (the top or bottom plate) running along the wall, and measure along it to find the correct spot. If there is no beam, locate the wall using one of these methods:[4]
    • Look for a row of nails in the subfloor, or a pair of joists very close together.[5]
    • Find a feature visible from both sides, such as a vent. Measure from there to the location you chose, then measure the same distance on the other floor.
    • If all else fails, drill a small test hole from the main floor to the attic or basement. Thread a pipe cleaner or similar object through and locate it on the other side.[6]
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    4
    Cut through the drywall. Return to the main floor and cut out a piece of drywall where the wire will exit:[7]
    • If installing an electrical box, trace the outline onto the drywall to get the exact dimensions. Otherwise, just draw a rectangle.
    • Drill two holes in opposite corners of the rectangle.
    • Slowly cut along the outline from one hole to the other, using a manual drywall saw.
    • If you need to patch the hole afterward, cut at an inward slant and remove in one piece.
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    5
    Drill through on the other side. Return to the attic or basement, and drill through the wall plate where you want to guide the wire through. You may encounter nails, so choose a drill bit that won't get damaged by metal.[8]
    • If you're working in a crawlspace, you can use a flex bit drill to drill this hole from several feet away.
    • Keep the hole at least 1¼" from the edge of the wood.[9] If this does not allow for a hole large enough to insert your wires, separate the wires and insert them through separate, smaller holes, spaced a reasonable distance apart.

Part 2
Fishing the Wires

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    1
    Pull the cable through with a fish tape. Carefully extend the fish tape from one opening to the other. Tape the end of the fish tape onto the cable with electrical tape. Retract the fish tape to pull the cable through.
    • Move slowly to avoid snagging the cable or damaging it due to kinks or friction.[10]
  2. 2
    Drop a string from above instead. If you want to bring the wire up to the attic, tie something to a string and lower it through the hole from above. Once the string reaches the bottom, go down to the lower opening and tie the cable and string together. Pull the string from above to fish the wire through.
  3. 3
    Draw the wire along with a magnet. A magnet may be the most effective method for long vertical distances or tricky corners. The key is to place the magnet at the stationary end, so it does not attach itself to a metal object in the middle of your wall:[11]
    • Tape a powerful magnet (such as a rare earth magnet) onto the end of the cable.
    • Stick the magnet and cable through one opening.
    • Tie an iron nail or similar object to a fish tape (or a string if the fish tape is not long enough).
    • Lower the nail on the fish tape through the other opening, until it makes contact with the magnet.
    • Remove the magnet and attach the cable end to the fish tape using electrical tape.
    • Retract the fish tape up to thread the cable through.

Part 3
Troubleshooting

  1. 1
    Approach lath and plaster construction with caution. Old plaster tends to break off the wooden lath easily, which makes installation much more difficult. If possible, mount electrical boxes next to a joist for a sturdier support.[12] Be prepared to repair the plaster after installation.
  2. 2
    Drill through fire blocks. If there are horizontal fire blocks between studs, you have two options:[13]
    • Use a flex bit to drill through the center of the fire block.
    • Or cut through the drywall at the fire block, and chisel out a notch ¾-inch wide x 1-inch deep (1.9 x 2.5 cm). Cover the notch with a metal nail plate after pulling the cable through.
  3. 3
    Thread wires past insulation. If the wall contains insulation, try to fish the wire between the outer paper or plastic cover and the wall. If there is no cover, press the wire against a stud and use it as a guide.[14]
    • While handling fiberglass insulation, wear gloves, eye protection, and a mask that covers your mouth and nose.[15]
  4. 4
    Cut through drywall for horizontal fishing. If there is no way to avoid fishing your wire horizontally, you will likely need to cut through the drywall. A small cut with a penknife is usually enough to let you guide the wire through.[16] In most cases, you will also need to drill through a wall stud as described below.
  5. 5
    Drill through studs or joists as a last resort. If there is no open path for the wire, you may need to drill through wall studs or ceiling joists. Follow these guidelines to avoid causing structural damage:[17]
    • Wall stud: drill through the center of the stud, using a maximum diameter of 60% of the stud's width (40% for load-bearing walls).
    • Ceiling joist: center the hole vertically, not through the top or bottom 2" (5 cm). Avoid the ends of the joist as well as the middle third. Maximum diameter is ⅓ of the actual depth of the joist (not the depth as labeled).
    • Vital support structures: Never drill through "glue lams" (laminated support beams), or through supports above doors, windows, or arches.
  6. 6
    Seal holes in fire blocks with fire-resistant caulk (recommended). Wiring through unprotected holes can allow a fire to spread rapidly between floors of your house. If you drilled through a fire block in your wall, or through fire-resistant flooring material, seal up the holes with fire-resistant caulk or a similar product.[18]

Tips

  • If there is no room behind the wall, install the wires in a raceway in front of the wall instead.[19]

Warnings

  • Be careful when using a flex bit. Once it breaks through, stop and tap the bit to see what you are going to hit next. PVC pipe, ductwork, and other objects make a different sound than wood.
  • Check power requirements before installing a new wire, to avoid overloading the circuit.[20]
  • Use only wires rated for in-wall use by a reliable third party such as Underwriters Laboratories. Wires should meet additional requirements if you plan to run them underground (direct burial), or if they are exposed to heat.[21] Look up the wire code online if you are not sure what it means.

Things You'll Need

  • Stud finder
  • Drywall saw
  • Wire coat hanger
  • Fish tape
  • Electrical tape

You may also need:

  • Rare earth magnet
  • String
  • Fire-resistant caulk

Sources and Citations

  1. http://www.homedepot.com/c/running_electrical_wire_through_walls_HT_PG_EL
  2. http://www.crutchfield.com/S-dBuOl2zfwn4/learn/learningcenter/home/inwall_wiring.html
  3. http://www.todayshomeowner.com/how-to-run-wires-in-existing-walls-and-floors/
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Article Info

Categories: Electrical Maintenance