Perimeter Trunking Sizes: A Complete Guide for Electrical Contractors
- Matt Neale
- 2 days ago
- 5 min read
Specifying the right perimeter trunking size is one of those things that sounds straightforward until you are standing on site with the wrong profile. A trunking system that is too small creates problems with cable capacity and future modifications. One that is too large looks wrong in the finished space and wastes money. Getting it right at the quoting stage saves time, return visits and awkward conversations with the client.
This guide covers the standard perimeter trunking sizes used in UK commercial installations, what each is typically used for, and how to match the right profile to the job.
What Is Perimeter Trunking?
Perimeter trunking is a surface-mounted cable management system that runs along the base of walls, at dado height, or at skirting level in commercial buildings. It provides a neat, accessible route for power and data cables without the need to chase into walls.
It is most commonly specified in offices, schools, healthcare facilities and other commercial spaces where cabling needs to remain accessible after installation and where aesthetics matter to the end client.
The system typically consists of a back section fixed to the wall and a clip-on lid, along with a range of accessories including internal and external angles, flat bends, end caps and joint covers.
Standard Perimeter Trunking Sizes
Perimeter trunking is manufactured to standard sizes that relate to the overall dimensions of the profile. Sizes are expressed in millimetres and refer to the height and width of the trunking body.
Skirting Trunking
Skirting trunking sits at floor level and is designed to replace or sit alongside a standard skirting board. It is the most common choice for open-plan offices and meeting rooms where floor-level cable access is needed.
Common skirting trunking sizes include:
100 x 50mm, the most widely used skirting size in commercial office fit-outs. Provides a large cable capacity suitable for mixed power and data runs. Suitable for most standard commercial projects.
150 x 50mm, used where higher cable volumes are needed or where the project requires three-compartment separation for power, data and telecoms. Commonly specified on larger open-plan floors.
75 x 25mm, a slimmer profile used where cable volumes are lower or where a less obtrusive finish is required. Common in smaller office spaces and retail environments.
50 x 25mm, the smallest standard skirting size. Suitable for single-compartment runs with limited cable volume, typically data-only or power-only circuits.
Dado Trunking
Dado trunking is installed at desk height, typically around 900 to 1000mm from the finished floor level. It is the preferred choice in open-plan offices where desktop power and data access is needed without floor-level trunking.
Common dado trunking sizes include:
150 x 50mm, the standard dado size for most commercial office projects. The depth accommodates power and data in separate compartments, and most UK socket and faceplate ranges are designed around this profile.
100 x 50mm, used where lower cable volumes are anticipated or where the budget is tighter. Still accommodates standard faceplates but with less internal space for future additions.
170 x 50mm, a deeper dado profile used on projects where three-compartment separation is required across a wide run. Less common but specified on some larger corporate and public sector projects.
Multi-Compartment Options
Where projects require strict separation between power, data and telecoms circuits, multi-compartment trunking provides internal dividers within the same profile. This avoids the need for separate trunking runs while keeping cable types separated to BS standards.
Two-compartment and three-compartment options are available across most standard sizes. The compartment configuration is typically specified at the quoting stage once the number of circuit types is confirmed.
How to Choose the Right Size
The right perimeter trunking size for a project comes down to three things: cable volume, compartment requirements, and the finished appearance the client expects.
Cable volume is the starting point. Count the number of cables that will run through the trunking and calculate the total cross-sectional area. A general rule of thumb is that cables should occupy no more than 45% of the internal trunking space to allow for heat dissipation and future additions. Underestimating at the specification stage is the most common cause of problems on site.
Compartment requirements depend on whether power and data circuits need to be separated. Most commercial projects require at least two compartments. Healthcare and some education projects may require three. Check the specification and any applicable standards before ordering.
Aesthetics matter more than many contractors expect. On a well-finished commercial project, the trunking needs to look intentional. A 150 x 50mm dado trunking in a high-spec office boardroom looks considered. A 100 x 50mm skirting trunking in the same space might look like an afterthought. It is worth discussing the profile size with the client or interior designer where the finished appearance is a key part of the brief.
Accessories and Fittings
A perimeter trunking system is only as good as its accessories. Internal and external angles, flat bends, end caps, joint covers and adaptor boxes all need to be compatible with the main trunking profile. When sourcing from a single supplier, this compatibility is straightforward. When mixing suppliers, check part compatibility carefully before ordering.
Standard accessories for UK perimeter trunking systems include:
Internal angles (for corners within the room)
External angles (for outside corners)
Flat angles (for changes in wall plane)
End caps
Joint covers
Conduit adaptor boxes
Flush and grid socket faceplates
Cutterwell perimeter trunking is compatible with standard UK accessories and faceplates, and the full range is available through the online catalogue for wholesalers with a trade account.
Supplied in 3 Metre Lengths
Cutterwell perimeter trunking is supplied in 3 metre lengths, which is the standard length for UK commercial installations. This minimises waste on most room dimensions and makes handling and installation straightforward for contractors.
When calculating quantities, allow for waste at corners and joints, and order slightly over the calculated linear meterage to account for cuts.
Stocking for Your Wholesaler Customers
If you supply electrical contractors working on commercial fit-out and refurbishment projects, perimeter trunking is a product that needs to be on the shelf rather than on order. Contractors working to programme cannot wait for non-stocked items, and if your branch cannot supply it, they will go elsewhere.
The most practical approach is to hold the standard skirting and dado sizes in the most common configurations, 100 x 50mm and 150 x 50mm in two-compartment, and order the less common sizes against specific project requirements.
Cutterwell supplies perimeter trunking exclusively through the UK electrical wholesale market from our manufacturing facility in Flint, North Wales. Strong stock levels and direct dispatch from our UK site means you can order with confidence and supply your customers without delays.
View the Cutterwell Perimeter Trunking Range
The full Cutterwell perimeter trunking range is available to order through the trade portal. If you are not yet a Cutterwell stockist and would like to discuss adding the range to your branch, get in touch with the team.