When you enter your home improvement center or hardware store you will be confronted with a multitude of potentially confusing electrical box options. Some electrical boxes are metal and others non-metallic (plastic). Some are for new wall construction (called "new work") and some are for renovations to an existing wall.
When you need to add an outlet or switch in an existing wall, you need to use a special electrical box called an "old work box."
An old work electrical box may be metal or plastic and is specially designed to be installed in an existing wall where it has no support other than the wall itself. Unlike electrical boxes you use for new construction which attach to a wall stud, old work boxes rely on a pretty cool clamping system that pinches the box between the front and back of the drywall.
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. Since the job of an old work box is to hold the electrical box in place in an existing wall, you will not be fastening the box to a wall stud. It will be located in a wall position where it has no support. That's why the box needs its own mounting system.
In the tutorial How to Install an Electrical Box in an Existing Wall, I will provide you detailed, photo-rich "how-to" instructions on easily installing the old work electrical box. Included in the tutorial are tips for making the box installation go much smoother and faster so you will be up and running quicker.