Electrical boxes are an essential component in any electrical wiring system, as they provide a safe and secure way to connect wires and protect them from damage. There are several different types of electrical boxes available, each with its own specific uses and benefits. In this article, we will take a look at the main types of electrical boxes and their uses. Understanding the different types of electrical boxes and their uses can help you make informed decisions when wiring your home or office.
Types of Electrical Boxes
The main types of electrical receptacle boxes are the followings:
1. Metal boxes
Electrical metal boxes are a vital component in any electrical system. These boxes are used to house electrical wiring, switches and outlets. They are available in a range of shapes and sizes to fit various electrical systems.
Metal boxes, formerly the norm in home building, are now utilized less frequently. Because they are nonconductive, less expensive, and easier to install, nonmetallic boxes are more common. Metal boxes, however, do have three key advantages over nonmetallic boxes: They are sturdy, come in a wider variety of patterns, and are frequently stackable. The rectangular switch or outlet box can be made single, double, or triple in size by stacking. In situations where the required design is only accessible in metal, such as along a basement or garage block wall, or in which the entire box is visible and vulnerable to damage, metal boxes are still required.
Handy or utility, boxes are the most misused of all metal boxes. The common rounded corner, 11⁄2-in.-deep box is only allowed one 14-gauge cable with switch or receptacle—anything more is a cable-fill violation. However, I don’t know of any electrician who hasn’t installed one or two 12-gauge cables with receptacles in a handy box. And when the cables were pushed in and power applied—bang. When volume is needed in metal boxes, 4-in.-square boxes or larger are the best to have around. To keep the insulated wires from being cut by the back of the box, consider insulating the back of the box with electrical tape.
When using a pancake box, make sure that you do not create a cable-fill violation by putting anything in it other than one cable. Some lights have round bases with such little depth that they won’t fit over the 1/2-inch. pancake; in that case, you must recess the box into the wall.
The ability of some metal boxes to change from a single gang box to an endless number of gangs by simply removing a screw is a significant advantage that metal boxes have over plastic.
2. Nonmetallic boxes
Plastic boxes, commonly referred to as electrical nonmetallic boxes, are a form of electrical enclosure used to house and safeguard electrical components and wiring. The majority of receptacle boxes used in residential construction are nonmetallic. They are both inexpensive and non-conductive. Although materials vary, the most common are flexible PVC plastic, rigid plastic and fiberglass. These boxes are typically used all over the house, but if the entire box needs to be surface-mounted in a living space, a common rectangular box shouldn’t be utilized, like the integral-nail box. Additionally, hanging lights shouldn’t be installed in the typical rectangular, nonmetallic box. Boxes with a wider attachment screw than typical boxes are indicated as being made for hanging lights.
Receptacle boxes differ from switch boxes in that they rarely have more than a double gang (two duplex receptacles in a box). Switches commonly use three- and four-gang boxes for all the switching required at entryways.
The most commonly used receptacle is a single-gang, nail-on box. For this type of box, simply nail the box to the stud, leaving just enough sticking out to be flush with the finished wall. Three challenges occur here: getting the distance out from the stud exactly right, keeping the box parallel to the stud and keeping the box from being distorted or broken as it is nailed onto the stud. To prevent the first two, take your time. Some boxes even have raised edges or ribs to help you judge the distance out from the stud. In addition, you can use a piece of 1/2-inch. plywood as a spacer to help get the distance right. Hold the plywood to the stud and align the edge of the box with the plywood.
To prevent breaking the box as you nail it in, simply tap the nails—don’t drive them hard as the nail head comes close to the box. The more precisely you get the box mounted on the stud, the less trouble you’ll have making the receptacle fit against the finished wall. If you don’t want to be bothered by constantly solving these problems, install the slightly more expensive side-mount box. This box has a bracket mounted to its side that nails to the front of the stud, placing the box at a prescribed distance (normally 1⁄2 in.) out from the stud and keeping its face parallel to the stud. This box will not work with thin wood panel walls.
To finish off a basement, it is common to frame out by placing 2×4s flat against the wall.
Installing them flat may increase the usable square footage of the room, but it does not allow much room for ordinary outlet boxes. Instead, you have to use a large 4-in.-square by 11⁄2-in.-deep nonmetallic boxes. Though shallow, the large footprint is big enough to accommodate both outlets and wires. Be sure to attach the box with drywall nails so the drywall can fit flush to the wall adjacent to the box.
3. Cut-in boxes
To install receptacle boxes in existing hollow walls, special boxes called old-work or cut-in boxes are used. These boxes do not mount to studs; instead, they attach directly to the finished wall, using plastic ears in front and supports (either swivel ears or wings, also called spring ears or clamps) in the back. The plastic ears hold to the drywall surface and the supports in the back sandwich the drywall to hold the box in place. In addition, you can make any box with drywall ears work like a cut-in box, as long as you have an adapter to do so. Remember, if you’re installing a cut-in box in a wall with a receptacle directly on the other side, offset the new box a bit so that the boxes are not back-to-back (usually there’s not enough room in the wall cavity to do this). Be wary if you install a cut-in box in a wall that separates the house from the garage. Once you cut into the wall you have opened a firewall—meaning that you have just created an opening for a garage fire to enter the house.
Cut-in boxes allow for a few errors during installation. The attachment system on the cut-in box will only work if the hole is small enough for the box’s plaster ears to press onto the finished wall front. If the electrician is sloppy and cuts the box hole too big, the box will simply fall through the hole. A good electrician will cut the hole exactly to fit the box. Some manufacturers furnish templates to aid in cutting out the hole. However, with other manufacturers, you’re on your own.
If you accidentally cut a hole that’s too big for the box, cut a thin cedar shim (the kind used to shim doors and windows) 2 in. to 3 in wider than the hole. Put some glue on the shim, slip it into the hole and pull it back against the inside of the finished wall. Once this is dry and secure, cut a piece of drywall the exact size needed to make the opening the correct size and glue it on top of the stick.
4. Weatherproof boxes and covers
Made from both plastic and cast metal, weatherproof boxes are used outside the house when the entire receptacle box will be exposed. Because of aesthetics, new construction locates most receptacle boxes for outside outlets inside the exterior walls. This also allows contractors to use less expensive standard boxes with weatherproof covers. When adding an outlet to a finished outside wall, a weatherproof box is normally attached to the outside siding. Even though the box is weatherproof, the receptacle still needs to be protected with a weatherproof cover.
There are two types of weatherproof covers: weatherproof while the cover is closed and weatherproof while the receptacle is being used. These fit onto the front of any type of box in lieu of a common cover plate. Most of us are familiar with the metal spring-loaded caps that snap down over the receptacle or GFCI outlet—these are watertight only when the cap is closed and are no longer code-compliant—a weatherproof-while-in-use cover must be installed. Code-approved covers come in two designs: a bubble type that extends off the receptacle and wall (to house the cord plug while it’s inserted into the receptacle) and a type that extends into the wall to allow the cover to be flush with the exterior wall (made by TayMac®). The latter is better (considerably less ugly) but it takes a 2×6 stud wall to house both the box and the recessed cover.
The bubble type is best when you want to convert an existing outside outlet by just replacing the lid. The problem with some watertight-while-in-use designs is that some are not watertight as advertised—although water does not rain in, it can leak in. To make it really watertight during driving rain, there must be a seal around the sides and top. Another problem I’ve found is that the bubble does not extend far enough away from the receptacle to plug in a thick extension cord and close the lid. If the lid is not completely closed, the whole design is void. Be aware that most designs only work for light-duty, easily bendable cords.