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Electrical Boxes in the Home
Electrical boxes are critical components of your home's electrical system. 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.Continue to 2 of 10 below.
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Metal and Plastic Electrical Boxes
Most electrical boxes are either metal or plastic. If you are using metal conduit to run wiring to the electrical box, then a metal box is required—to anchor the conduit and because the conduit and metal box system itself may be used to ground the system. If you are using 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).Continue to 3 of 10 below.
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Round Pan Electrical Box
Round pan, or "pancake," boxes typically are only 1/2-inch or 3/4-inch deep. They are used most commonly for ceiling- or wall-mounted light fixtures that weigh no more than 50 pounds. 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.Continue to 4 of 10 below.
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Octagon and Round Electrical Box
Octagon and standard-size round boxes range from 1 1/2 to 2 1/8 inches deep and are the standard box for ceiling- or wall-mounted light fixtures weighing up to 50 pounds. 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.Continue to 5 of 10 below.
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Ceiling Fan-Rated Electrical Box
Ceiling fan boxes come in several different types and sizes, including 1/2-inch-deep "pancake" versions and standard 2-1/8-inch-deep boxes. They are usually round but may be octagonal.
Note: Must be Ceiling fan boxes must be UL-listed for ceiling fan mounting and marked “For Use With Ceiling Fans.” Do not use standard boxes for installing ceiling fans. Ceiling fan boxes require special fastening to withstand the dynamic loading of a rotating fan.
Most ceiling fan boxes are rated for fans or light fixtures weighing up to 75 pounds, depending on the installation method. 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.Continue to 6 of 10 below.
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4-Inch Square Box
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 multiple conductors in two or more directions. They are also commonly used as junction boxes and can also be installed in ceilings or walls for supporting lighting fixtures or housing switches or receptacles.Continue to 7 of 10 below.
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A junction box is not a special type of box but rather any standard electrical box used to enclose wire splices. The standard box used for junctions is a 4-inch square box, which offers plenty of space for making wire connections with multiple wires or cables, but other type of boxes can be used for this application.
Junction boxes must be installed where they are always accessible; never install a junction box in a concealed wall or ceiling space where the box cannot be accessed in the future. Junction boxes also must be covered with solid covers with no holes.Continue to 8 of 10 below.
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Electrical Box Covers
Electrical box covers come in a wide variety of sizes and shapes to match different types of boxes. A cover is used to enclose the front of the box and is required by code; it is unsafe, and usually illegal, to leave an electrical box uncovered.
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.Continue to 9 of 10 below.
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Box extenders, or extension rings, come in a variety of sizes and shapes to match standard electrical boxes. They are shaped like boxes but have no back. They are designed to be installed onto the front of standard electrical boxes to increase the box capacity or to bring the box flush with the drywall or other surface material.Continue to 10 of 10 below.
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Outdoor Electrical Box
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.