Electrical boxes are critical components of your home's electrical system that encase wire connections to protect them from short circuits. But for many DIYers, the wide variety of boxes is bewildering. There are plastic and metal boxes; "new work" and "old work" boxes; round, square, and octagonal boxes; and boxes with load ratings for ceiling fans and heavy light fixtures.
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.
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Metal and Plastic Electrical Boxes
- Best for: Metal-sheathed cable or metal conduit (metal boxes), Romex or non-metallic cables (plastic boxes)
Most electrical boxes are either metal or plastic: Metal boxes are generally made of steel, while plastic boxes are either PVC or fiberglass. Weatherproof metal boxes for outdoor use are generally made of aluminum.
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).1:30
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Standard Rectangular Boxes
- Best for: Single light fixture switches and outlet receptacles
Standard rectangular boxes, also known as "single-gang" or "one-gang" boxes, are typically used for single light fixture switches and outlet receptacles. They are generally about 2 x 4 inches in size, with depths ranging from 1 1/2 inches to 3 1/2 inches. Some forms are gangable—with detachable sides that can be removed so the boxes can be linked together to form larger boxes for holding two, three, or more devices side by side.
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.
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2-Gang, 3-Gang, and 4-Gang Boxes
- Best for: Multiple electrical devices encased together
Like standard rectangular boxes, gangable electrical boxes are used to hold household switches and electrical outlets, but they are oversized so that two, three, or four devices can be mounted side-by-side. Like other boxes, these come in a variety of "new work" and "old work" designs, some with built-in cable clamps.
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).
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Round Pan Electrical Boxes
- Best for: Ceiling- or wall-mounted light fixtures weighing less than 50 pounds
Round pan, or "pancake," options are shallow circular boxes that are most commonly used for ceiling- or wall-mounted light fixtures that weigh no more than 50 pounds. These can be only 1/2 inch or 3/4 inch deep, and they can be made of plastic or durable metal (with similar affordable prices). Some types of specially rated metal pan boxes may be used for mounting ceiling fans, but not all pan boxes may be used for this purpose.
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.Continue to 5 of 11 below.
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Octagon and Round Electrical Boxes
- Best for: Ceiling- or wall-mounted light fixtures weighing up to 50 pounds
Octagon and standard-size round boxes are deeper than round pan boxes, and they are the standard box for ceiling- or wall-mounted light fixtures weighing up to 50 pounds. These boxes range from 1 1/2 to 3 inches deep with similar costs to round pan options. They provide much more room for wiring than shallow round pan boxes and can be used as junction boxes.
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.
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Ceiling Fan-Rated Electrical Box
- Best for: Ceiling fans up to 70 pounds or light fixtures ranging from 90 to 150 pounds depending on the fixture rating
Ceiling fan electrical boxes are typically used for fans weighing up to 70 pounds or light fixtures weighing up to 90 pounds (or more), depending on the installation method. They come in several different types and sizes, including 1/2-inch-deep "pancake" versions and standard 2 1/8-inch-deep boxes. Ceiling fan boxes are usually round but can be octagonal, and are either made of metal or durable plastic. They are often a bit pricier than other electrical boxes, but many affordable options can be found at most hardware stores.
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.
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4-Inch Square Box
- Best for: Multiple conductors running in two or more directions
Square boxes come in standard depths of 1 1/4 to 2 1/8 inches, but their square corners give them additional interior space, providing maximum volume for multiple conductors and connectors. For this reason, 4-inch square boxes often are used to run several conductors in two or more directions.
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.
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- Best for: Enclosing wire splices
A junction box is not a special type of box, but rather a term used to describe any standard electrical box used to enclose wire splices. The standard box used for junctions is a 4-inch square box (either metal or strong plastic), which offers plenty of space for making wire connections with multiple wires or cables, but other types of boxes can be also used for this application. Costs vary based on the type of junction box chosen.Continue to 9 of 11 below.
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Electrical Box Covers
- Best for: Enclosing various types of electrical boxes
Electrical box covers are used to enclose the front of the box and are required by code; it is unsafe, and usually illegal, to leave an electrical box uncovered. Covers come in a wide variety of sizes, shapes, and materials to match different types of boxes (which can vary in price, but are typically less expensive than the box itself).
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.
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Outdoor Electrical Box
- Best for: Outdoor electrical needs
Weatherproof outdoor boxes are sealed enclosures designed for mounting to the surface of exterior walls, roof overhangs, decks, and other structures. They are used for installing outdoor receptacles (outlets) and light fixtures. Outdoor boxes must have an outdoor cover or fixture rated for damp or wet locations, depending on the application.
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.
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- Best for: Increasing box capacity and making boxes flush with surfaces
Box extenders, or extension rings, come in a variety of sizes and shapes to match standard electrical boxes. They are designed to be installed onto the front of electrical boxes to increase the box capacity or to bring the box flush with the drywall or other surface material.
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.
Choosing an Electrical Box
While there are a variety of electrical boxes to choose from, it's most important to use each box for its intended purpose. For example, round pan boxes should only be used when their capacity is large enough for the wires they must encase, and ceiling fans or heavy light fixtures should always be mounted on boxes that are rated for the fixture's weight.
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.