Helpful video reference. We reference the Artisan Electrics video "PVC Conduit CRASH COURSE! Installing 35+ Metres!" as the video reference here. Artisan Electrics is a Cambridge-based professional electrical company with an extensive UK YouTube channel covering real-world installation techniques. This video shows a substantial conduit installation in practice, including bends, fixings and cable drawing.
1. When to use PVC conduit
PVC conduit suits any situation where cable needs mechanical protection and surface trunking would look out of place or be impractical. Common uses in UK domestic properties include:
- Garage and workshop wiring where cables run along exposed brick or block walls.
- External runs down the outside of a building before entering the ground.
- Cable entry points through walls where a trunking lid would not seal properly.
- Runs through cavity walls or ceiling voids where a rigid oval conduit protects the cable.
It is not always the right choice. Inside plasterboard studwork, oval conduit or clipping behind the board is less intrusive. In finished living rooms, surface trunking blends better. Use the right tool for the job.
2. Choose the right diameter
Standard UK domestic conduit diameters are 20 mm and 25 mm. 20 mm covers the vast majority of domestic jobs. Use the BS 7671 Appendix 5 tables (or the IET On-Site Guide) to confirm cable fill: the conductors must not occupy more than 40 per cent of the conduit's internal cross-sectional area. In practice, 20 mm conduit comfortably accepts:
- One or two 2.5 mm² two-core and earth flat cables (short straight runs).
- Three or four 2.5 mm² single-core cables on a straight run.
- A single 6 mm² two-core and earth flat cable.
Step up to 25 mm if you are pulling 10 mm² cable for a dedicated appliance circuit, or if you need more than four single-core conductors on a run with bends.
3. Plan the route and mark fixing positions
Walk the route and note every bend, tee junction and end termination. Where possible, keep runs horizontal or vertical — diagonal conduit looks sloppy and is harder to add to later. Mark clip positions at no more than 750 mm on horizontal runs, and 1000 mm on vertical runs.
For runs with multiple bends, work out the set distances in advance. A conduit bender's saddle mark and the multiplier table on the bender handle let you calculate how far back from the bend centre to start the set. Measure twice before you cut.
4. Fix the clips first
Drill and plug each clip fixing point before threading conduit. This is much easier than trying to hold conduit in position and drill at the same time. Use correctly sized conduit saddles: a 20 mm saddle for 20 mm conduit, a 25 mm saddle for 25 mm. On masonry walls, a 6 mm or 7 mm masonry plug and 30 mm round-head screw works well.
5. Cut conduit to length and form bends
Cut conduit square with a hacksaw, then clean up the cut end with a deburring tool, a conduit reamer, or just a half-round file. Sharp burrs will score conductor insulation when you pull the cable through.
Form bends with a conduit bender. For 20 mm conduit, a simple manual bender does the job. Press slowly and evenly to get a smooth curve: rushing creates a flat spot or kink. For 90-degree corners at boxes or in tight spaces, use a manufactured elbow fitting rather than bending sharp — a tight bend reduces cable fill and makes pulling harder.
Solvent-weld fittings with PVC conduit cement where the joint needs to be permanent and weatherproof. On indoor inspection runs where you may want to access the cable, use push-fit couplers and leave the joints unglued.
6. Feed conduit into the clips
Thread each length of conduit into its saddles from one end to the other before fixing the saddle screws fully. This lets you adjust the alignment before committing. Tighten saddles enough to grip without cracking the conduit.
7. Draw cable through
Feed a draw tape (also called a fish tape or conduit rod) through the installed conduit run. Attach the cables to the draw tape hook securely, folding the conductor ends back on themselves and taping them smooth so they do not snag on the conduit bore or joints. Pull firmly and steadily. For runs over five metres or with more than two 90-degree bends, a cable lubricant (pulling compound) reduces friction significantly.
Single-core cables pull through more easily than flat T&E. If you are using T&E, make sure you run all cores of the same circuit together.
8. Make off the ends correctly
Fit a plastic conduit bush (also called a locknuts bush) on every cut end where conductors emerge. This prevents the sharp edge of the conduit from cutting conductor insulation over time. At junction boxes, use a circular three-entry box (BESA box) that accepts conduit entries directly. At consumer units or isolators, pass the cable through a grommet.
9. Test before energising
Before connecting either end, run an insulation resistance test at 500 V DC between each pair of conductors. On a new run you expect to see well above the minimum 1 MOhm, usually many hundreds of MOhm. Then check continuity of the circuit protective conductor with a low-reading ohmmeter or multifunction tester. Only when both tests pass should you connect and energise.
When to call us
Running conduit for an existing circuit is within reach of a handy homeowner with the right tools. But designing the circuit, sizing the MCB, running back to the consumer unit and certifying the work under Part P is a qualified electrician's job. If the conduit is part of any new circuit, call an electrician to carry it out or at minimum to inspect and certify it before the supply is connected.
Richard covers electrical installation and certification work across Sandwich and east Kent.
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