How To Choose an Electrical Box

Selecting the right electrical box for your project can be confusing because of the many options available. Whether you’re starting new construction or adding to existing wiring, understanding the different types of electrical boxes helps for a safe installation. We’ll break down the categories of electrical boxes and explain their uses. Heath Eastman, an electrical expert at This Old House, discusses the differences between electrical boxes.

Types of Electrical Boxes

Electrical boxes come in many styles, each designed for specific purposes. Understanding these differences will help you choose the right box for your project.

New Work Boxes

New work boxes are used in new construction or when walls are opened up for renovations. These are designed to be installed before drywall or other wall coverings are in place. Features of new work boxes include nailing flanges for easy attachment to studs, pre-embedded nails, and plastic or metal options.

Plastic new work boxes are commonly used with non-metallic cable wiring. They offer quick installation and are good for most residential applications. Metal new work boxes are preferred when using metal-clad cables. These provide better grounding and bonding capabilities.

Old Work Boxes

Old work boxes, or retrofit boxes, are used in existing walls where access is limited. These boxes allow you to add new electrical devices without affecting your drywall. Old work boxes are designed to be installed in finished walls, have tabs or clamps that grip the drywall from behind, and are available in both plastic and metal.

The most common old work box has tabs that pop out when pushed into the wall, securing the box to the drywall. Another option has angled brackets inside the box, allowing you to screw through the box and into a stud without opening the wall.

Single-Gang vs. Double-Gang Boxes

Electrical boxes are also categorized by the number of devices they can accommodate. Single-gang boxes hold one electrical device, such as a switch or receptacle. Double-gang boxes accommodate two electrical devices side by side. 

For larger installations, you can find boxes that accommodate three or more devices. The choice between single-gang and double-gang boxes depends on your wiring needs and the number of devices you plan to install.

Multi-Gang Boxes

Multi-gang boxes are best for situations where you need multiple devices in a single location. These range from three-gang to six-gang boxes, providing space for switches, receptacles, dimmers, or combination outlets. Multi-gang boxes are used for control panels or sectioned wiring in larger rooms and commercial spaces.

Material Considerations for Electrical Boxes

It’s important to know the different materials available for electrical boxes. You can decide between plastic or metal boxes, each with its own pros and cons.

Plastic Boxes

Plastic boxes are the most common choice for residential wiring projects. They are lightweight, easy to install, and less expensive than metal options. Plastic boxes are also non-conductive, reducing the risk of electrical shock, and they’re compatible with non-metallic cable wiring. Plastic boxes are a good option when using non-metallic cable (NM cable or Romex).

Metal Boxes

Metal boxes are required in some situations and have some unique benefits. They provide better heat dissipation, durability, and fire resistance. These boxes also include built-in clamps for metal-clad cables and have knockouts for conduit connections. Metal boxes are required for proper grounding and bonding of your electrical system.

Specialized Electrical Boxes

Certain applications require specialized electrical boxes for safety and proper installation. Depending on where you’re installing an electrical box, you’ll need to use some different options.

Round Boxes for Light Fixtures

Round electrical boxes are used for wall-mounted light fixtures, such as sconces. They are designed to support the fixture’s weight and provide a secure mounting point.

Ceiling Boxes for Heavy Fixtures

You’ll need a specialized ceiling box designed to handle more weight to support heavier ceiling fixtures like chandeliers. These come with additional bracing that can be attached to joists or other supporting structures to distribute the weight evenly.

Fan-Rated Boxes for Ceiling Installations

When installing ceiling lights or fans, you must use a fan-rated box. You should always install fan-rated metal boxes for ceiling fixtures, as these are designed to support the weight and movement of ceiling fans.

Additional Electrical Boxes

Outdoor boxes are built to withstand outdoor elements and often come with weatherproof covers or gaskets to protect the electrical components from moisture. Junction boxes join multiple wires and are used in residential and commercial spaces for organization and code compliance.

Choosing the Right Electrical Box for Your Project

Selecting the appropriate electrical box depends on several factors, including construction, wiring method, devices, location, and safety.

Type of Construction

Your project’s construction type influences the choice of an electrical box. For new constructions, new work boxes are best, while old work boxes are better for renovations.

Wiring Method

The type of cable you’ll use also affects your choice. Non-metallic cables pair best with plastic boxes, while metal-clad cables need metal boxes.

Number of Devices

Determine how many devices you plan to install in a single location. Single-gang boxes are good for individual switches or outlets, while multi-gang boxes are used for multiple devices.

Location and Use

The specific use of the box will also determine the features you need. For instance, ceiling installations benefit from fan-rated boxes, while outdoor setups require weatherproof boxes.

Safety Considerations

Safety is most important during any installation. Make sure that the box can handle the power requirements and environment where it’s installed. Metal boxes have great grounding and durability, which can be best in moisture-prone or high-traffic areas.

Electrical Box Installation Tips

Proper installation is important for the safe use of electrical boxes. Make sure the box is securely fastened to the framing or wall structure, and use the appropriate fasteners and methods listed by the manufacturer. Maintain proper box fill calculations to avoid overcrowding. Keep boxes accessible and use approved cable clamps or connectors when bringing wires to the box.

Additional Installation Snippets

Run your wiring before the walls are fully closed up, which will help you make fewer mistakes during the wiring process. Always double-check local codes for requirements related to your installation. If you’re unsure, consult a licensed electrician for professional advice.

Managing Overcrowding

Box fill calculations are required to avoid overcrowding, which can lead to overheating or short circuits. Most boxes will have a maximum capacity noted by the manufacturer. Following these recommendations will make for a safer and more reliable electrical system in your home.

Special assistance with this project was provided by Eaton and Eastman Electric.