7 Tips for Electrical Box Installation

Mount Electrical Box Between Studs If Necessary

Electrical boxes typically are mounted to the sides of studs for stability. Whether nailed to the studs or screwed in with adjustable brackets, boxes on studs tend to stay in place for a long time.

But sometimes, it's not always possible to find a suitable mounting point against the studs. What about between the studs?

Using old-work electrical boxes is one way to hover the boxes between studs. Old-work boxes attach directly to the drywall, not to the studs.

After cutting a rectangular hole in the drywall, you insert the electrical box in the hole. Then, with either a manual Phillips screwdriver or a cordless drill/driver, you turn the two screws clockwise.

Turning the screws also turns the two plastic wings behind the drywall, forcing the box against the drywall. While it's not as strong as a stud-mounted box and sometimes the wings will break off, often it's the only option when you want the box to be between studs.

Install Wall Boxes at Uniform Heights

There are no precise code guidelines for how high wall switches or outlet boxes should be positioned. But professionals follow certain standards for a uniform look. Whatever standard you choose, try to maintain uniformity for all electrical boxes. Irregular box heights will flag a home's electrical work as that of an amateur.

Wall Switches

It is standard practice for wall switches to be installed about 48 inches above the floor. But this distance can range from 43 to 53 inches, depending on your preference. For spaces used by people with accessibility issues requiring a wheelchair, for example, lower switch heights might be practical.

Outlet Boxes Over Flooring

The common practice for receptacle outlet boxes is to install them so the bottom edge is between 12 and 16 inches above the floor. This distance, too, can be adjusted for special circumstances.

Outlet Boxes Over Countertops

For switches and outlets above countertops, install them so the bottoms are about 4 inches above the countertop surface.

Use a Drywall Reference Strip

In new construction, attaching a strip of drywall to the front face of studs can serve as a guide for attaching wall boxes. Without some kind of guide, it can be difficult to install the boxes with the proper offset to ensure the front edges of the electrical boxes will be flush with the finished drywall surface. 

When you install an electrical box, make sure it is flush with the surface of this drywall strip; this will ensure the boxes are at the proper depth when the walls are finished.

Most residential drywall is 1/2- or 3/8-inch thick, so keep a handful of drywall strips of this thickness on hand to facilitate electrical box installation. If you are using a different wall thickness (such as 5/8-inch thick, required for some firewalls) make sure the reference strips match that thickness.

Use the Box's Measuring Tab

Plastic nail-in electrical boxes may have 3/8-inch measuring tabs along the sides. You can use these to indicate how far to extend the electrical box from the face of the studs.

Begin by slightly pushing out the nails on the box by hand, so that when you place the box against the stud, the tips of the nails lightly pierce the wood. This helps hold the box in place during those first couple crucial strikes of the hammer as you drive the mounting nails into the stud.

Hammer Box Nails Carefully

Plastic electrical boxes can be fragile. When nailing the box, use light, careful blows rather than heavy swings of the hammer. Make sure to keep your blows perpendicular to the stud. If you strike too hard, you risk pushing the box backward along the face of the stud. Take extra care during cold weather: If you strike the box itself in low temperatures, the box could shatter or break.

Alternate Blows Between Nails

Rather than hammering in one nail fully before proceeding to the next one, it's best to alternate back and forth between the nails, hammering each nail in about 1/4-inch each time. This will keep the box from twisting or deflecting as you attach it.

Some electricians stop just short of driving the mounting nails completely into the studs. This allows the box to be easily removed should the layout need to be changed before the NM cable installation.

Use Metal Boxes to Relieve Cord Strain

Most household electrical boxes carry one or two lightweight cords, typically for lights, appliances, computers, or phone chargers. These thin cords place very little strain on the outlet and electrical box, so even a plastic box will work in most cases.

But certain cords are thicker and heavier, placing a dangerous amount of strain on the outlet and the box. Dryer cords are attached to 240 V outlets, and while the cords aren't frequently moved, they do place a heavy, constant burden on the outlet box.

Similarly, a 240 V, 40 A Level 2 electric vehicle charging station is commonly attached to a NEMA 14-50 outlet. The less expensive Level 2 EV chargers have no wall station, so they plug directly into the outlet. This action places a great deal of strain on the outlet, day in and day out. Chargers that have permanent wall stations are less likely to add strain to the outlet—more like permanently attached dryer cords.

With any type of larger, 240 V outlet, it's often best to use a metal box, especially for cords that are frequently removed and replaced.