01 of 09
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. Here's a look at the most common types of boxes for household applications, to help you get the right parts for your next project.Continue to 2 of 9 below.
02 of 09
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 wiring, such as Type NM-B (nonmetallic 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).
Metal boxes come in types known as:
- Drawn steel (1-piece construction)
- Interlocked/gangable (typically for switch and outlet boxes); these can be joined together to create a larger box
Plastic boxes can be made from different types of molded plastic and are almost always 1-piece construction. They can be made from:
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- PVC (most common)
- Phenolic resin
03 of 09
Round Pan Electrical Box
1/2-inch and 3/4-inch deep
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- Metal box is typically used for ceiling- or wall-mounted light fixtures up to 50 pounds
- Plastic box may used for outlet mounting
- 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 (see Ceiling Fan-Rated Electrical Boxes, below)
04 of 09
Octagon and Round Electrical Box
1-1/2 inch to 2-1/8 inches deep
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- Typically used for ceiling- or wall-mounted light fixtures up to 50 pounds
- May be used as a junction box
- Metal box may also be used as a switch or outlet box in surface-mounted installations using metal conduit
- Round plastic box often has "ears" for fastening to wall or ceiling in existing or "old work" applications
05 of 09
Ceiling Fan-Rated Electrical Box
1/2 inch to 2-1/8 inches deep
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- Must be UL-listed for ceiling fan mounting and marked “For Use With Ceiling Fans”
- May be a round or octagon shape
- Requires special fastening due to dynamic loading of rotating fan
- Depending on weight rating and installation, may accommodate installation of ceiling fan and light fixture up to 75 pounds or more
- May be mounted directly (with four screws) to a ceiling joist or wood blocking or may attach to adjustable brace spanning between ceiling... joists
06 of 09
4-Inch Square Box
1-1/4 inches to 2-1/8 inches deep
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- Square boxes provide maximum volume for multiple conductors and connectors; often used to run multiple conductors in two or more directions
- Commonly used as junction boxes with solid covers
- Square boxes may be installed in ceilings or walls for lighting fixtures, switches, or receptacles
07 of 09
Electrical Box Covers
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- Covers are used to enclose an outlet box and are required by code; never leave a box uncovered
- Switches or receptacles may be installed into square or octagon boxes by using covers with cutouts
- Octagon or round covers are used for mounting light fixtures
- Raised 4-inch square covers are used for mounting switches or receptacles
- Flat, round closure plates are designed for use in dry locations to enclose unused ceiling boxes
08 of 09
1-1/4 inches to 2-1/8 inches deep
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- A junction box is an electrical box used to enclose wire splices
- Junction boxes must be installed where they are always accessible; never install a junction box in a concealed wall or ceiling space where is cannot be accessed in the future
09 of 09
- Box extenders or extension rings are like boxes with no back; they are 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