Helpful video reference. Nick Bundy of N Bundy Electrical, a NAPIT-registered electrician from Staffordshire, shows a real domestic trunking installation in his video "Dado Trunking in a House? Home office Sockets — Electrician". The job is running circuits in a home office using surface-mounted trunking rather than chasing — which is exactly the scenario this guide covers. The fixing method, corner pieces and socket mounting he uses are the standard approach for UK domestic trunking work.
1. Understand when trunking is (and is not) the right answer
Surface trunking works well for: adding sockets or a data circuit to a home office, running a new circuit along a brick or concrete wall that cannot be chased, improving the appearance of an existing surface cable run, and creating accessible, maintainable cable routes in a workshop or utility space.
It is not the right answer where the trunking itself would be at serious risk of mechanical damage (forklift paths, heavy vehicle areas), where it cannot be secured to the wall properly (crumbling plaster, or surfaces that will not hold a screw), or where an occupier might regularly interfere with the lid and expose live conductors.
In most domestic rooms, though, it is a perfectly legitimate installation method and a qualified electrician will use it routinely where conditions call for it.
2. Choose the right type of trunking
PVC trunking comes in several profiles:
- Mini trunking (16 x 16 mm or 25 x 16 mm) — for single cable runs, lighting drops, or data cables alongside the skirting board or at picture rail height.
- Standard single-compartment trunking (38 x 25 mm, 50 x 25 mm) — suits two or three mains cables side by side, common for adding a socket circuit or an FCU spur.
- Dado trunking (two or three compartments, 150 mm or 170 mm tall) — the larger profile used at dado height (roughly 900 mm from the floor) in offices and home offices, separating mains from data in different compartments.
- Skirting trunking — replaces the existing skirting board, hiding both data and power cables behind a deeper profile at floor level.
For a home office with mains sockets and Cat 6 data cable, a two-compartment dado trunking keeps band 1 (data) and band 2 (mains) separated as BS 7671 requires. For a single socket spur across a brick wall, standard single-compartment trunking is perfectly adequate.
3. Calculate the cable fill
BS 7671 Regulation 522.8.1 limits cable fill to 45 percent of the internal cross-sectional area of the trunking. This is not pedantic: over-filled trunking traps heat, which degrades cable insulation and can reduce the current-carrying capacity of every cable inside it.
Add up the external cross-sectional areas of all the cables you plan to run (the manufacturer's data sheet gives this, or measure the diameter and calculate the area). If the total exceeds 45 percent of the trunking's internal area, go up a size. When in doubt, go bigger — trunking is cheap, and a sensible person leaves room for the cable run they will add in three years.
4. Plan the route and order the accessories
Walk the full cable route and mark every bend, junction and end point. Count the accessories you need:
- Internal corners (for runs that go around a corner inside the room)
- External corners (for runs that turn around the outside of a wall)
- Flat tees (for spur branches)
- End-caps (to close open ends neatly)
- Couplers (to join two lengths of trunking in a long straight run)
- Surface mounting boxes for sockets and switches (the same trunking manufacturer usually makes them)
Buy 10 percent more trunking than the measured length — mitre cuts and off-cuts add up.
5. Fix the trunking base to the wall
Snap a chalk line or use a spirit level to mark the run line before screwing anything. This takes five minutes and saves the embarrassment of a visibly cocked trunking run.
Screw the base channel to the wall at centres of no more than 500 mm (300–350 mm gives a neater result and less flex in longer runs). Use wall plugs in masonry or brick, timber screws directly into studwork. The screws go through the centre of the base channel where the lid clip conceals the screw head.
Cut the base channel and lid to length with a junior hacksaw or fine-tooth mitre saw. A mitre box gives cleaner 45-degree angled cuts for corners — PVC trunking manufacturers sometimes also supply pre-formed plastic corner pieces that avoid the need for mitred cuts altogether. Both are acceptable; the factory corners are faster and look consistent.
6. Route the cable
Feed the cable through the base channel before clipping the lid. For short runs this is straightforward. For longer runs (anything over three or four metres), use a cable fish tape or draw wire to pull the cable through.
Keep mains cables (band 2) in one compartment and data or communications cables (band 1) in another, or in separate runs of trunking. If both types must share the same trunking body, a divider strip is required. Mixing them without separation fails BS 7671 and can introduce noise onto data lines.
Do not force cables around tight bends — use the manufacturer's corner accessories instead. Kinked insulation is a slow fault waiting to happen.
7. Make all joints in accessible enclosures
This is where people sometimes go wrong. A connector or junction inside a sealed length of trunking is not accessible for inspection or maintenance. BS 7671 requires all electrical joints to be accessible. The right place for a junction is inside:
- A surface-mounted back box behind a socket or switch faceplate
- A maintenance-free junction enclosure (Wago B2B or similar, rated and accessible behind an appropriate cover)
- A surface-mounted adaptable box
Never make a joint midway along a trunking run without providing an accessible enclosure at that point.
8. Fit the lid and final accessories
Once all cables are routed and connections made, clip the lid onto the base channel along the full run. Press firmly at each clip point so it snaps home evenly. Fit end-caps, corner pieces and coupler covers. The completed run should feel solid with no flexing or rattling when pushed.
Surface back boxes for the sockets or switches screw through the base channel into the wall behind. The socket faceplate then screws to the back box in the usual way.
9. Test before restoring power
Before switching the circuit back on, carry out a basic continuity and polarity check with a continuity tester or multimeter:
- Confirm earth continuity from the source earth to every new socket earth terminal
- Confirm line and neutral are not reversed at any socket
- Confirm there is no short circuit between line and neutral
If you are adding a new circuit rather than extending an existing one, the new circuit needs a full set of initial verification tests to BS 7671 before the Electrical Installation Certificate is issued. That is work for a qualified electrician with the correct test equipment.
When to call us
Running a surface trunking spur from an existing socket or FCU is within reach for a careful homeowner who can work safely around isolated circuits. The moment it turns into a new circuit from the consumer unit, or you discover the existing wiring is old or suspect, that is the point to call a qualified electrician. New circuits are Part P work in England and Wales and need a certificate on completion.
Richard covers Sandwich, Deal, Dover, Ramsgate and east Kent. Free quotes for new circuits, extensions and home office wiring.
Adding sockets or circuits in east Kent?
Richard wires new circuits and surface trunking installations across Sandwich and surrounding towns. Clean work, proper certification, fixed price agreed before the job starts.
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