Metal Back Boxes

About Metal Back Boxes

Metal back boxes are essential electrical components used to house and support sockets, switches, and other wiring accessories in both domestic and commercial installations. Manufactured from durable pre-galvanised steel, these robust mounting boxes provide a secure fixing point for electrical accessories while protecting the wiring connections behind. Unlike their plastic counterparts, metal back boxes offer superior strength and are often preferred in solid wall installations where chasing into brick or blockwork is required.

The metal back boxes available from Tooled-Up.com are manufactured to British Standard BS 4662, ensuring compliance with UK electrical regulations. These boxes feature multiple knockouts around the perimeter, allowing cables to enter from various angles depending on the installation requirements. Available in single and double gang configurations, metal back boxes typically have a depth of 25mm or 35mm, with the deeper versions providing additional space for cable terminations and reducing the risk of damaging conductors when fitting accessories.

Whether you're installing 240v sockets, light switches, or other electrical accessories, metal back boxes provide the structural integrity and fire resistance needed for safe, long-lasting installations. Their galvanised finish offers excellent corrosion resistance, making them suitable for use in a wide range of environments from new builds to refurbishment projects.

Jargon Buster

• Knockouts: Pre-scored circular or oval sections in the back box that can be easily removed to allow cables to enter the box from different directions. Most metal back boxes feature multiple knockouts for maximum installation flexibility.
• Gang: Refers to the number of electrical accessories the back box can accommodate. A single gang box houses one socket or switch, while a double gang box accommodates two.
• Box Depth: The measurement from the front face to the back of the box, typically 25mm or 35mm. Deeper boxes provide more space for cable connections and are essential when using thicker cables or multiple connections.
• Pre-Galvanised Steel: Steel that has been coated with zinc before fabrication to prevent rust and corrosion, ensuring durability in various installation environments.
• BS 4662: The British Standard specification for metal boxes for electrical accessories, ensuring products meet minimum safety and quality requirements for UK installations.
• Lugs: The fixing points on a back box where screws secure the faceplate or electrical accessory. Metal boxes typically feature threaded lugs for reliable fixing.

Who Uses Metal Back Boxes?

• Electricians and Electrical Contractors: Professional sparkies use metal back boxes daily for first and second fix electrical installations in residential, commercial, and industrial properties.
• Builders and Construction Companies: Required during the build phase when installing electrical infrastructure in new developments and extensions.
• Maintenance Engineers: Facilities and maintenance teams use metal back boxes when upgrading or repairing electrical systems in existing buildings.
• Renovation Specialists: Tradespeople working on refurbishment projects who need to replace damaged or outdated back boxes.
• Property Developers: For bulk installations across multiple units in residential and commercial development projects.
• Competent DIY Enthusiasts: Homeowners undertaking electrical work within the scope of Part P Building Regulations, such as like-for-like replacements.
• Landlords and Property Managers: When maintaining electrical installations in rental properties to ensure compliance with safety standards.

How to Choose the Right Metal Back Boxes

Gang Configuration: Determine whether you need single or double gang boxes based on the number of electrical accessories being installed. Single gang boxes accommodate one socket or switch, while double gang boxes house two adjacent accessories.

Box Depth: Standard 25mm depth boxes suit most installations, but consider 35mm deep boxes when dealing with multiple cable entries, thicker cables, or when installing USB charging sockets which require additional internal space. The extra depth at Tooled-Up makes cable management significantly easier and reduces the risk of damaging conductors.

Wall Type: Metal back boxes are particularly suited to solid walls (brick, block, or concrete) where they can be firmly secured using suitable fixings. Ensure the box depth is appropriate for the wall construction and available chasing depth.

Knockout Positions: Check the knockout arrangement suits your cable entry requirements. Most boxes feature knockouts on all four sides and the back, but verify this matches your installation needs.

Quantity Requirements: Metal back boxes are often sold in packs of 5 or 10, making them cost-effective for larger projects. Calculate your requirements carefully to ensure you have sufficient boxes plus a few spares.

Compliance and Standards: Always choose metal back boxes manufactured to BS 4662 to ensure compliance with UK electrical regulations and Building Regulations Part P.

Popular Accessories

• Electrical Sockets and Switches: The primary accessories fitted to metal back boxes, available in various configurations including 240v power sockets, light switches, and dimmer switches.
• Grommets and Bushes: Protective inserts for knockout holes that prevent cable damage from sharp metal edges.
• Dry Lining Boxes: Alternative mounting solutions for plasterboard and stud wall installations where metal back boxes may not be suitable.
• Plaster Depth Boxes: Shallow profile boxes designed for installations with limited depth available.
• Mounting Screws and Fixings: Appropriate wall plugs and screws for securing metal back boxes in various wall types.
• Cable Clips and Trunking: For securing and routing cables to and from the back boxes.
• Electrical Testing Equipment: Socket testers and multimeters for verifying correct installation and safe operation of 240v circuits.

Safety Information

Electrical Work Regulations: All electrical work in the UK must comply with Part P of the Building Regulations and BS 7671 (IET Wiring Regulations). Notifiable work must be carried out by a registered electrician or certified upon completion by Building Control. Only competent persons should undertake electrical installations.

Isolation: Always isolate the electrical supply at the consumer unit and verify the circuit is dead using an approved voltage tester before commencing any work on electrical installations.

Earthing: Metal back boxes must be properly earthed when used with metal faceplates or accessories. Ensure earth continuity is maintained throughout the installation and verify with appropriate testing equipment.

Cable Protection: When cables pass through knockouts, fit appropriate grommets or bushes to prevent sharp metal edges from damaging cable insulation, which could lead to short circuits or electric shock hazards.

Fire Resistance: Metal back boxes provide excellent fire resistance, but ensure proper installation depth and that surrounding materials meet fire safety requirements, particularly in cavity walls.

Frequently Asked Questions

Do I need a metal or plastic back box?
Metal back boxes are generally preferred for solid wall installations as they offer superior strength and fire resistance. They're ideal when chasing into brick or blockwork. Plastic dry lining boxes are typically used in plasterboard and stud walls. Metal boxes are mandatory in certain commercial and industrial applications.

What depth metal back box do I need?
For standard socket and switch installations, 25mm depth is usually sufficient. However, 35mm deep boxes are recommended when installing USB sockets, dealing with multiple cable entries, using larger cable sizes (such as cooker or shower circuits), or when you need extra space for cable terminations.

How do I secure a metal back box in a solid wall?
First, chase out the wall to the appropriate depth using a bolster chisel or power chasing tool. The box should sit flush with the finished plaster surface. Secure using appropriate wall plugs and screws through the fixing holes, or use plaster/filler to hold the box in position once cables are connected.

Can I use the same back box for sockets and switches?
Yes, metal back boxes are universal mounting solutions suitable for 240v sockets, light switches, dimmers, cooker switches, and other electrical accessories of the same gang configuration. The accessory faceplate simply screws into the lugs on the back box.

Are metal back boxes sold individually or in packs?
Metal back boxes are typically sold in packs of 5 or 10 units, making them economical for larger electrical installations. This bulk packaging is particularly convenient for electricians and contractors working on multiple room installations or new build projects.