How to Install a Cut-In Electrical Box With Madison Straps
Measuring and Cutting Drywall & Safely Securing the Box
Installing a new electrical box in a finished wall requires a special type of box, often called a retrofit, remodel, cut-in, or old work box. Old work boxes are designed to be installed after the walls are closed and are used during remodeling projects. They attach to drywall or plaster.
Old work boxes are most commonly made of plastic with built-in ears or wings that secure the box to the drywall. They attach to studs. By contrast, a new work box is designed to be installed after the wall is framed but before the surfaces are finished with drywall.
What Is a Cut-In Box?
A cut-in box is an electrical box that goes in after a room or wall has been completed. You must cut into the wall to make space for the electrical box. These boxes enclose wire connections and help protect against short circuits, which can cause fires. They are most commonly used for electrical fixtures, like light switches, fire alarms, ceiling fans, and outlets. Cut-in boxes come in many shapes and materials and have multiple uses, depending on what needs wiring.
Electrical Cut-In Boxes: Different Shapes, Materials, and Sizes
Electrical cut-in boxes are either metal or plastic and can come in various shapes and sizes. Metal boxes are generally made of steel, while plastic boxes are either PVC or fiberglass. Weatherproof metal boxes for outdoor use are usually aluminum. A metal box is required for running wiring to an electrical panel; it anchors the conduit and metal grounds the system. Plastic boxes are used mainly for non-metallic cable, such as Type NM-B (non-metallic sheathed cable), requiring the cable to be secure to the box with an appropriate cable clamp.
Cut-ins come in different shapes based on the purpose, such as round cut-in boxes that are used for ceiling- or wall-mounted light fixtures. Round ceiling cut-in boxes are designed to hold up to 50 pounds of weight, while other types made specifically for ceiling fans can hold up to 90 pounds.
The standard, single-switch size is 2 inches by 4 inches, with depths ranging from 1 1/2 inches to 3 1/2 inches. While 4-inch boxes are used as junction boxes or for multiple conductors and connectors running in different directions.
Before You Begin
Before you get started, plan where you will place your new electrical cut-in box by measuring up from the floor and leveling as you go. Also, determine if you are using a plastic or metal electrical box.
When installing a plastic electrical cut-in box, you will need to cut a hole in the drywall, slip the box into place, and turn a couple of screws to pull the ears or wings tight to the backside of the drywall. But if you use traditional old metal work boxes used by electricians (typically on commercial jobs), they are installed similarly but use a different attachment system. They rely on thin strips of metal, called Madison straps or "Mad bars," tucked into the gap along both sides of the box.
The Madison straps keep the box from slipping out of the cutout opening. The straps have rear tabs that rest against the backside of the drywall, as well as front tabs that are folded over the edges of the box to hold the straps in place. Like plastic old work boxes, metal boxes have flanges on the front edge, preventing the box from falling into the hole.
Madison straps are easy to install. For a professional-looking job, it's essential to cut the drywall hole carefully so that the box fits and is adequately supported and the outlet cover plate hides all gaps.
How to Install a Cut-In Electrical Box With Madison Straps
What You'll Need
Equipment / Tools
- Tape measure
- Torpedo level
- Drop cloth
- Drywall saw
- Linesman pliers
- Metal old work electrical box
- 2 Madison straps
Mark the Hole for the Box
Measure up from the floor and mark the wall where the top of the electrical box will be located. Hold the electrical box against the wall so the top is flush with the mark, and use a torpedo level to adjust the box so it is level. Use a pencil to trace along the outside of the box onto the wall. This will be the outline for the cutout.
Note: Do not trace around the flanges, or metal tabs, at the top and bottom of the box. The cutout should be a rectangle; do not cut the area behind the flanges.
Cut the Hole
Cover the floor below the work area with a drop cloth to catch dust. Punch the point of a drywall saw through the drywall just inside of the marked outline, then use the saw to complete the cut. As you finish the cut, try to grip the cutout piece to extract it from the opening (although it's not a problem if it drops back into the wall cavity; you can leave it inside the wall).
Insert the Electrical Box
Fit the electrical box into the hole. If the fit is too tight, you may have to trim the opening slightly to enlarge it. Push the box fully in so that the box flanges are tight against the face of the drywall.
Install the Straps
Insert the metal straps, one on each side of the box, with the longer end facing up, and slide the strap in past the back surface of the drywall. Then, slide the strap down until it is centered in the hole. Pull the strap outward so it is tight against the back of the drywall.
Bend the Straps
Fold over both tabs on each strap while simultaneously pulling outward on the tab and pushing inward on the box. Bend the tabs over the box edge, either by hand or with linesman pliers, than bend the tabs flush against the inner surface of the metal box with the pliers. Secure all four tabs to complete the installation. The box should fit tightly into the opening with a minimal amount of wiggling.
Once you've run the wires, you are ready to install the outlet, switch, or other device in your new electrical box.
Do you install outlets before drywall?
If hanging new drywall, install all wiring and electrical boxes for wall outlets, switches, and light fixtures before the drywall. Otherwise, you will have to do cut-ins.
How can I secure my electrical box without studs?
Cut-in electrical boxes secure into the drywall or plaster using wing screws or Madison straps, depending on the type of box you have. The wings press against the drywall and hold the box firmly in place. Likewise, Madison straps secure the box by grabbing on behind the drywall to support the box.
Can I run electrical wire outside of drywall?
You can run electrical wire outside of drywall, but it's not ideal aesthetically. The place where it's least noticeable is along the baseboard, floor, or molding. If running electrical wire outside drywall, use armored cable and screw clamps to the wall to secure it.