All of the most commonly used boxes for home wiring projects are available at home centers and large hardware stores, and it’s important to know the differences in order to buy the correct box for each job. Here, we’ll break down the different types of electrical boxes you need to know to safely install the correct models around your home. If you are using metal conduit to run wiring to the electrical box, then a metal box is required—both to anchor the conduit and because the conduit and metal box itself may be used to ground the system. Metal boxes are more durable, fireproof, and secure. Plastic boxes are typically cheaper in price and include built-in clamps for wires. If you are using a non-metallic cable, such as Type NM-B (non-metallic sheathed cable), then you can use either plastic boxes or metal boxes, as long as the cable is secured to the box with an appropriate cable clamp. Modern wiring systems with NM-B cable usually include a ground wire inside the cable, so the box is not part of the grounding system (however, metal boxes must be connected to the system ground, usually with a short length of wire called a pigtail). Standard rectangular boxes come in various types of “new work” and “old work” designs, and they can be metallic or non-metallic (with metallic being more durable). Some types have built-in cable clamps for securing NM cables. These boxes can range in cost, but most standard options are very affordable. The same effect can be created by using standard rectangular boxes with a gangable design that allows the sides to be removed so the boxes can be joined together to form larger boxes. Gangable electrical boxes are most often made of durable galvanized steel, however, some plastic snap-together options may be found at certain hardware stores (sometimes for a slightly higher price). It’s important that the fixture wires can be properly connected and fitted within the round pan box. These are shallow electrical boxes with only enough space for fitting a few electrical connections. If there are more wire connections to be made, you will probably need a full-sized octagon or round electrical box with more volume. The number of wires in the electrical box should never exceed its safe fill capacity. Metal boxes are suitable for surface-mounted installations using metal conduit. Round plastic boxes often have “ears” for fastening to the wall or ceiling surface in existing or “old work” applications. These allow you to secure the box to the drywall (or other surface material) rather than cutting a large hole in the drywall to fasten the box to the framing. Boxes can be mounted directly (with four screws) to a ceiling joist or wood blocking, or they can attach to adjustable braces spanning between ceiling joists. They are also commonly used as junction boxes, for installation in ceilings or walls to support lighting fixtures, or to house switches or receptacles when matched with the proper cover plates. Like other types of electrical boxes, square boxes can be made of metal or plastic, and they can be found for low prices at most hardware stores. Solid, or “blank,” covers have no holes and typically are used with junction boxes or for enclosing unused boxes. Covers for 4-inch square boxes may have special cutouts to accommodate switches or receptacles (outlets). These typically include a raised center area that extends the box so the opening for the switch or outlet will be flush with the exposed surface of the drywall or other wall or ceiling finish. Plastic outdoor boxes are usually made from high-impact PVC, while metal outdoor boxes are typically made from aluminum rather than steel. Prices may be higher for specialty options, but most standard outdoor boxes are comparable in cost to indoor boxes. Box extenders are shaped like the boxes they’re intended for but without a back panel. Metal or plastic extenders should be used to match the material of your electrical box. If you’re unsure which type of electrical box you need, it’s helpful to ask an electrician or a professional at your local hardware store for guidance. In addition to choosing the type of box you need, you must also determine whether you need an “old work” or “new work” electrical box. If you are replacing an existing electrical box, an “old work” style will be needed to attach the box to the wall covering (usually drywall). When building a new house or an addition, “new work” boxes can be used to attach directly to the stud.
