How to Use an Electrical Box Extender

By
Timothy Thiele
Timothy Thiele

Timothy Thiele has an associate degree in electronics and is an IBEW Local #176 Union Electrician with over 30 years of experience in residential, commercial, and industrial wiring.

Learn more about The Spruce's Editorial Process
Updated on 11/09/22
Electrical box adding an extender behind a light switch

The Spruce / Kevin Norris

Project Overview
  • Working Time: 30 mins - 1 hr
  • Total Time: 30 mins - 1 hr
  • Skill Level: Beginner
  • Estimated Cost: $10 to $15

The electrical code requires that all electrical boxes, including those holding outlets, switches, or light fixtures, must be installed so that the front face is flush with the wall surface. This is to ensure that the box is sealed and the wires inside properly protected. Sometimes an electrical box is improperly installed so that the front edge of the box is recessed back into the wall—a problem that occurs most often during remodeling, such as when new paneling or backsplashes are installed over an existing wall surface. Fortunately, there is an easy fix—a device known as a box extender.

Box extenders are metal or plastic rings available in varying sizes and depths to fit snugly around or just inside an existing electrical box. When installed over an existing box, they extend the box so it is flush with the front face of the wall, thereby creating a code-approved enclosure for the wire connections inside.

What You'll Need

Equipment / Tools

  • Non-contact circuit tester
  • Screwdriver

Materials

  • Box extender
  • Device mounting screws (if needed)

Instructions

Materials and tools to use an electrical box extender

The Spruce / Kevin Norris

  1. Choose the Correct Box Extender

    Box extenders are available in several sizes and shapes to match different box sizes and different depth needs. Make sure to choose one that matches the outer dimensions of your electrical box, and one with a depth that closely matches the gap between the face of the wall and the front of the recessed electrical box. Your extender needs to cover the gap around the box fully, and it may overlap the box slightly when you insert it. It doesn't matter the material of your box, you can get a box extender in either material.

    Electrical box extender sized to match outside dimensions of box

    The Spruce / Kevin Norris

  2. Turn Off the Power

    The first step to installing the box extender is to turn off the circuit that you'll be working on. Go to your electrical panel, whether it be a circuit breaker panel or fuse panel, and look at the listing chart on the door to identify the right circuit breaker or fuse. Switch off the circuit breaker or remove the fuse controlling the device in the electrical box you're working on.

    Circuit power being turned off in electric service panel

    The Spruce / Kevin Norris

  3. Check for Power and Remove the Device

    Check the outlet or switch for power using a non-contact circuit tester. Once you are sure the power is off, remove the mounting screws holding the outlet receptacle or switch to the electrical box. Gently pull the device out of the electrical box by pulling on the mounting strap. There is generally no reason to disconnect the circuit wires from the device.

    Non-contact circuit tester checking the switch for power

    The Spruce / Kevin Norris

  4. Attach the Box Extender

    Slip the box extender over the device and slide it into the electrical box. The fit should be tight. Usually, you can slide the extender over the switch or receptacle without disconnecting the circuit wires. If the circuit wires prove to be too short for the extended depth created by the extender, you can attach pigtail wires to the circuit wires to make the connections to the device.

    Blue box extender being slipped over the electrical box while holding the switch

    The Spruce / Kevin Norris

  5. Reattach the Device

    The holes for the mounting screws on the extender should match up exactly with the holes on the existing box. Push the switch or receptacle back into place, so the mounting holes on the strap line up with the holes in the box, then reattach the device to the box, using the mounting screws. If the existing screws are too short, you can replace them with longer screws to accommodate the added depth created by the extender.

    Light switch placed over extender and secured with mounting screws and straps

    The Spruce / Kevin Norris

  6. Attach the Cover Plate and Test

    Make sure the switch or outlet is level, then reattach the device's cover plate. Turn the power back on the main service panel and test the outlet or switch to make sure it is working properly.

    Cover plate placed over light switch and pressing the light switch

    The Spruce / Kevin Norris

FAQ
  • When would you use a box extender?

    If an electrical box is set too far back into the wall, an electrical box extender is used to make the box flush with the wall.

  • How does an electrical box extender work?

    Box extenders fit around the existing electrical box. They come in different sizes, so they can extend the box just enough that it’s flush with the wall.

  • Are outlet box extenders safe?

    When installed properly, electrical box extenders are safe. Just make sure the power is off (use a non-contact circuit tester to verify) before you start working to install one.