01 of 06
Metal Madison Straps: A Classic Method
When installing a new electrical box in an existing wall, the old-work boxes now used are usually designed with built-in wings or expandable ears that allow the box to be snugged up against the drywall. After inserting the box in the cut-out opening, tightening the ears draws the box up tight to the back surface of the wall, holding it in place.
But at one time, old-work boxes did not have these features, and electricians instead relied on strips of metal, often known as "Madison straps" or "Mad bars," that tucked into the gap along both sides of the box, with tabs that folded over the edges of the box to hold it against the wall surface. While the flanges on the box kept it from falling into the wall, the Madison straps were what kept the box from slipping out of the cutout opening.
The Madison strap method has largely been replaced by newer box designs, but there may be instances where this is still the most practical method. Here's how to use Madison straps.
Tools and Supplies You Will Need
Continue to 2 of 6 below.
- Old-work (retrofit electrical box)
- Tape measure
- Drywall saw or vibrating multi-tool
- 2 Madison straps
- Linesman's pliers
02 of 06
Mark the Cutout Hole
Measure up 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 level to adjust the box so it is level. Use a pencil to trace the outside of the box on the wall. This will be the outline for the cutout.Continue to 3 of 6 below.
03 of 06
Cut the Hole
Cover the floor below the planned cutout with newspapers or a drop cloth to catch the dust. Drill access holes along the outline for the electrical box, large enough for the tip of the drywall saw.
Use the drywall saw to complete the cutout, cutting along the marked pencil lines. As you complete the cut, try to grip the cutout piece to extract it from the opening (although it's not a problem if the cutout piece drops back into the wall cavity).
- Tip: Pros often make this kind of cutout with an oscillating multi-tool with a vibrating blade designed for drywall. It easily creates a clean, perfect hole for installing electrical boxes. If you happen to own one of these tools, try this technique.
Where necessary, now is the time when you should fish the electrical cables through the wall cavity and prepare them for inserting into the electrical box.Continue to 4 of 6 below.
04 of 06
Insert the Electrical Box
After cutting the hole in the drywall, fish the electrical cable through the hole, open knockout openings in the box, and secure the cables in the metal box with clamps. It is much easier to secure the cables now, just prior to fitting the box in the wall opening.
Now, insert the electrical box in the hole. If the hole 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.Continue to 5 of 6 below.
05 of 06
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 forward so it is tight against the back of the drywall.Continue to 6 of 6 below.
06 of 06
Bend the Straps
Fold the tabs on the strap over and bend them flush against the inner surface of the metal box, using linesman's pliers. Bend all four straps to complete the installation. Done correctly, the box should fit tightly into the opening with a minimum amount of wiggling.
You are now ready to install the outlet, switch, or other device in your new electrical box.