How to Install an Old Work Electrical Box in an Existing Wall

Electrical socket
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  • 01 of 10

    Installing an Old Work Electrical Box for a Switch or Outlet in an Existing Wall

    old work electrical box
    Old work electrical boxes are used in renovation applications and have tabs or "ears" that hold it fast against the back of an existing wall. © 2013

    Electrical boxes come in a seemingly endless variety of styles, including metallic (steel) versions requiring grounding of the box and nonmetallic versions (PVC, phenolic resin or fiberglass) which do not require grounding of the box. Electrical boxes are really not that complicated and are designed for two basic applications:

    • Where the box is being installed BEFORE the finished wall is installed (new work box).
    • Where the box is installed AFTER the finished wall is installed (old work,or retrofit,...MORE box). Old work boxes have opposing corner tabs or "ears" integral to the box that press against the back side of the wall as the fastening screws are tightened

    Metallic boxes can be used with either nonmetallic (Type NM-B) or metallic sheathed electrical cable. Nonmetallic plastic boxes are designed for use only with nonmetallic sheathed electrical cable.

    This tutorial will show you how to easily install an old work plastic electrical box into an existing wall for use with an outlet or switch.

    Difficulty Level

    • Easy

    Needed Tools and Materials

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  • 02 of 10

    Retention Tab Detail

    mounting ears on eletrical box
    Old work electrical boxes have retention tabs that tighten against the wall to hold the box in place against the mounting ears on the front of the box. © 2013

    Since the function of an old work box is to hold the box in place in an existing wall, the box will not be fastened to a wall stud. It will be located in a position where it has no support other than what it provides with its own mounting system.

    To remain firmly in place, these boxes have a pretty interesting fastening system that uses tabs or "ears" in opposite corners that pop up as the attaching screws are drawn tight. As the screws are tightened, the tabs press against the back side...MORE of the drywall or plaster, while mounting ears on the front of the box press against the front face of the wall, holding the box firmly in place.

    Now, a couple of tips to make use of the plastic old work box a little easier.

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  • 03 of 10

    TIP: Prep the Retention Tab Screw

    retention screw on electrical box
    Tighten the retention screw drawing the retention tab up about 1/4" and then back out the screw. © 2013

    The screw that goes into the retention tab on the box may sometimes be very tight. This may require you to put too much pressure against the wall when you  turn the screw, sometimes causing damage to the wall.  

    TIP: To avoid this problem, simply tighten the mounting screw BEFORE installation, drawing the retention tab up about 1/4" to 3/8". This effectively precuts the threads in the plastic retention tab, making the screw easier to turn later when you are actually securing the box in...MORE the wall. Once the screw is drawn up about 1/4" to 3/8", then back the screw out to allow the retention tab to go back into its original folded position.


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  • 04 of 10

    TIP: Prep the Box's PVC Electrical Cable Clamp

    opening of electrical box access tab
    Pry open the clamping tab about 1/4" to allow easier insertion of the NM-B cable. © 2013

    Old work electrical boxes made from PVC use an integrated quick-clamping system to hold the nonmetallic NM-B cable to the box. These clamping tabs can be a little difficult to get to open up.

    TIP: To make insertion of the power cable into the box easier, take a flat blade screwdriver and pry up the clamping tab about 1/4", allowing for easier insertion of the nonmetallic cable into the box.


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  • 05 of 10

    Prepare Electrical Box Opening in the Wall

    trace wall box profile on wall
    Trace the box profile on the wall where you want to cut the drywall. The use a hole saw to carefully cut the hole. © Carlon 2013
    1. Position the electrical box backward against the wall where you want it located. 
    2. Take a pencil and trace the outline of the box on the wall (Note: Some styles of boxes may require you to enlarge the hole slightly at the point where the retention tabs are located. If so, this will become apparent when you try to slide the box into the wall).
    3. Using a drywall keyhole saw, carefully cut the hole along the traced outline and remove the drywall blank.
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  • 06 of 10

    Strip Wire Sheathing from Electrical Cable

    wire conductors exposed from sheating
    Strip about 6" of sheathing from the power wire exposing the conductors and ground wire. © 2013

    Make sure the power wire that will be fed into the box has the power shut off to it by ensuring the circuit breaker is turned off to the wire.

    Once the hole is cut in the wall for the box, feed the power cable through the hole. Before the cable is fed through the old work box, use a cable stripper to  strip about 6" of the electrical sheathing from the NM-B cable exposing the conductors and ground wire.

    This can also be done by taking a knife or razor blade and slicing the sheathing PARALLEL...MORE to the wires, being careful not to slice the insulators, then carefully cutting the sheathing off.

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  • 07 of 10

    Insert Electrical Cable into Box

    electrical cable insterted into box
    Insert cable into the old work electrical box making sure the sheathing is firmly in place under the clamping tab. © 2013

    Thread the nonmetallic sheathed cable into the old work box, making sure the sheathing is securely under the clamping tab (PVC box) or clamping bar (phenolic resin / fiberglass box). Make sure to leave about 6" to 7" of exposed wires. You can either strip the wire ends now or later.

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  • 08 of 10

    Insert Old Work Box Into Wall

    inserting electrical box into wall
    Insert the old work box into the wall and tighten the two retention screws. © 2013

    Next, simply place the old work electrical box into the hole in the wall. Hold the box so the mounting ears on the front of the box are tight against the front of the drywall while you tighten the two retention screws. Turning the screws will flip the retention tabs so they can then be drawn against the back of the drywall securing the box to the wall.

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  • 09 of 10

    Strip Wire Insulation from Conductors

    stripping insulation from conductors
    Strip the insulation from the wires back about 3/4" to 1". © 2013

    Strip the insulation back about 3/4" to 1" back from the end of the wire conductors. You can use a wire stripping tool which makes short work of the task, as shown here. Or, you  can use a needle-nose pliers or wire cutter to score the insulation and pull it off the wires. Make sure not to cut into the metal wire conductors.

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  • 10 of 10

    Installed Box

    installed old work electrical box
    Completed box installation ready to be fitted with an outlet or switch device. © 2013

    Once the insulation is stripped from the wires and the box is firmly in place, the box is ready to receive a switch, or, in this case,  an outlet receptacle. Twist wire nuts onto the ends o the wires for safety until the final wiring connections are completed.