Electrical boxes used to mount outlets, switches, and light fixtures in walls and ceilings come in a seemingly endless variety of sizes and styles, including metallic (steel) versions requiring grounding of the box, and nonmetallic versions (PVC, phenolic resin, or fiberglass) which do not require grounding of the box. Metallic boxes can be used with either nonmetallic (Type NM-B) or metallic sheathed electrical cable. Nonmetallic plastic boxes are designed for use only with nonmetallic sheathed electrical cable.
Whatever the material, electrical boxes can be loosely divided into two types:
- New work boxes, designed to be installed just after the wall is framed but before the surfaces are finished with drywall. They attach to studs.
- Old work (also called retrofit) boxes, designed to be installed after the walls are finished and are used during remodeling projects. They attach to drywall or plaster.
Installing an old work box into an existing wall to add an outlet or wall switch is an easy project that requires just a few common tools that you may already own if you’re familiar with basic electrical repairs. The most difficult part of the project is running cable through the walls; this process can take several hours, even though the box itself can likely be installed in a matter of minutes.
Understanding How Retrofit Boxes Work
Before getting started, it helps to understand the purpose and anatomy of an old work electrical box.
An old work box is designed to be installed after the fact—on walls that are already finished. They are often used in situations where you are adding outlets or extending an existing circuit in a room that is already finished. Because these situations don’t allow you the opportunity to attach the box directly to studs, these boxes need a different means of anchoring.
To anchor them in place, these boxes have a clever fastening system that uses retention tabs and mounting ears located in opposite corners of the box. Once the box is inserted into the wall cutout and the screws are tightened, the rear retention tabs open up and draw up tight against the back of the drywall or plaster while mounting ears on the front of the box press against the front face of the wall. The front ears and back retention tabs essentially “pinch” the box tightly in place against the wall surface.
If you will be running live electrical wire to the new electrical box, it is absolutely essential that you turn off the circuit breaker that controls the circuit before you pull and attach the cable. If you don’t know which breaker to throw, you’ll want to turn off the main breaker, which will cut power to the entire house.
Watch Now: How to Install an Old Work Electrical Box
Source: The Spruce