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....Read Full Post