Metal framing has become increasingly popular in residential and commercial construction, and with it comes new challenges for attaching electrical boxes. Anchoring these boxes properly prevents short circuits and potential fire hazards. In this guide, we’ll walk you through selecting and attaching electrical boxes to metal studs for a safe and code-compliant installation.
Types of Electrical Boxes for Metal Studs
When working with metal studs, choosing the right electrical box is the first step in a secure installation. There are several types of boxes designed to use with metal framing, which we’ll dive into below.
Standard Electrical Boxes
Standard electrical boxes are the most common type used in residential construction. These rectangular boxes typically house a single electrical switch or outlet. For metal stud applications, look for boxes with special mounting features designed to work with metal framing. They often have strategic placements for screws and flanges that help secure them firmly to the metal studs.
Remodel Electrical Boxes
Also known as old-work boxes, remodel electrical boxes are used when adding switches or outlets to existing walls. While traditionally used with wood framing, some models work with metal studs with the right mounting techniques. Remodel boxes usually feature clamps or brackets that allow them to be secured to the cut drywall and the metal stud behind it.
GFCI Electrical Boxes
Ground-fault circuit interrupter (GFCI) outlets require deeper boxes to accommodate their larger size. When installing GFCI outlets on metal studs, choose a box with enough space and the right mounting options. Check that the box can handle the depth and connections without pinching the wires.
Materials Used in Electrical Boxes
The material used for an electric box can affect its durability, ease of installation, and how it works in different settings. Understanding the material options helps you choose the right box for metal stud installations.
Plastic Electrical Boxes
Plastic boxes are lightweight, affordable, and corrosion-resistant. They usually have mounting ears that make them compatible with wood and metal studs. However, grounding can be more challenging with metal studs. They are ideal for dry, indoor locations where fire resistance isn’t a huge concern.
Metal Electrical Boxes
Metal boxes are more durable and fire-resistant than plastic. They’re best for commercial use and in areas where more durability is needed. Metal boxes also have inherent grounding capabilities, which is helpful when working with metal studs. They typically have multiple knockouts for conduit entry, and you can easily bond them to the stud for effective grounding.
Composite Electrical Boxes
Composite boxes offer a middle ground between plastic and metal. They’re stronger than plastic and lighter than metal. These boxes can be a good choice for metal stud applications, as they balance durability and easy installation. Some feature flanges and braces that are compatible with metal stud systems.
Choosing the Right Electrical Box for Metal Framing
There are several factors to consider when choosing the best electrical box for your metal framing.
Box Material
While metal boxes are often preferable for metal stud applications, plastic boxes can be used under certain circumstances. Here are a few important considerations to keep in mind:
- Check local building codes to ensure plastic boxes are permitted for your specific application.
- Proper grounding is key. Run the equipment-grounding conductor into the box and connect it directly to the device’s green screw.
- Choose plastic boxes with appropriate mounting features for metal studs. They should come with mounting ears or brackets suitable for securing to metal.
- Consider the environment and application. Metal boxes may be required in certain commercial or high-heat areas, such as industrial kitchens or workshops, due to their higher durability.
Box Size and Capacity
The box size should accommodate the number and size of conductors it will contain. The National Electrical Code (NEC) has guidelines for minimum box sizes based on the number and gauge of wires. It’s also wise to factor in additional wiring space for future modifications or upgrades.
Mounting Features
Look for boxes with mounting features designed for metal studs. These may include:
- Metal tabs that fit into the slots on metal studs for a secure fit
- Attached tabs for screwing directly to the stud, which will keep it stable even with wire movement
- Bendable tabs that wrap around the front and rear of the stud, which provide strong anchoring, especially if the studs are spaced far apart
Steps to Attach Electrical Boxes to Metal Studs
Installing electrical boxes on metal studs requires attention to detail and adherence to local building codes. Follow these steps for a safe installation:
- Measure and mark the location of the electrical box on the metal stud: Use a level for accuracy, especially for installations requiring multiple boxes.
- Position the box against the stud, checking that it’s level and at the correct height: Double-check the alignment with neighboring boxes or fixtures. Most boxes will have a stop or tab that keeps the front of the box either ½ inch or ⅝ inch out from the stud to account for the depth of the drywall.
- Secure the box: Using an electric drill, secure the box with ¾-inch No. 6 self-tapping metal screws. The box will either have side tabs with pre-drilled holes for this purpose, or longer straps intended to wrap around the stud and attach through the sides. If using a box with bendable tabs, wrap them around the stud before securing them with screws.
- Make sure the box is flush with the front edge of the stud: This allows for proper drywall installation. An out-of-alignment box can complicate finishing work and potentially violate code requirements.
Advanced Methods for Electrical Box Installation
Beyond the basic steps above, there are advanced techniques that can improve the quality of your electrical box installation.
Manage Cable Entries
Attentive management of cable entries keeps the conductors well-protected and compliant with code requirements. Use appropriate cable clamps or bushings to prevent abrasion where cables enter the box. Metal boxes typically come with built-in clamps, but you can create additional protection with grommets or conduit entry fittings.
Insulate Between Metal and Conductors
To prevent accidental grounding or short circuits, consider using insulating materials such as gaskets or liners between metal boxes and conductors, especially in commercial settings. These insulating materials can prevent the metal from cutting into the wire insulation, reducing the risk of electrical faults.
Fire Ratings and Inspections
Fire-rated electrical boxes may be required in certain jurisdictions and building types. Check that boxes already installed in fire-rated assemblies comply with local fire codes. After installation, have a qualified inspector review the work to verify its compliance and safety, particularly for complex setups or commercial installations.
Tips for Working With Electrical Boxes and Metal Studs
To successfully install electrical boxes on metal studs, keep these tips in mind:
- Use a level to make sure the boxes are level before securing them.
- If necessary, pre-drill holes in the metal studs to prevent splitting or deformation, especially for older or thinner stud materials.
- Don’t overtighten screws, which can strip the metal or damage the box.
- If needed, use box extenders to flush the box with the finished wall surface, especially if your walls are thicker than usual.
- Follow manufacturer instructions for your box model and local building codes.
Common Mistakes To Avoid
Avoid the common mistakes below for a safe and proper installation.
Incorrect Box Selection
Using the wrong type or size of electrical box can lead to operational failures. Match the box type to the application, such as using GFCI-rated boxes for circuits requiring ground fault protection.
Overcrowding Boxes
Stuffing too many wires into a small box increases the risk of overheating and short circuits. Follow NEC guidelines on box fill calculations to avoid this issue.
Ignoring Grounding Requirements
Failing to ground your electrical boxes properly can lead to dangerous electrification of metal components. Follow all grounding procedures carefully.
Safety Considerations
Working with electrical systems requires caution and adherence to safety protocols. Always turn off power at the circuit breaker before beginning work, and verify with a non-contact voltage tester before you get started.
Wear appropriate personal protective equipment, including safety glasses and gloves. Use insulated tools when working near live electrical components to reduce the risk of electric shocks. If you feel unsure about any aspect of the installation, hire a licensed electrician to prevent dangerous and costly mistakes.
