Rigid PVC electrical conduit is a core protective component in concealed electrical works. Installation quality directly affects cable service life and electrical safety. Problems such as snagged cable pulling, cracked bends and leaking joints mostly stem from non-standard operation - only by following the correct procedure can long-term conduit reliability be ensured.
1. Cable Pulling
The total cross-sectional area of cables inside the conduit (including insulation) shall not exceed 40% of the conduit internal area, allowing space for heat dissipation and future replacement. Calculation shall be based on the measured cable outer diameter. DN20 typically carries 3 × 2.5mm² copper conductors, and DN25 carries 3 × 4mm²; for multi-circuit or large-cross-section cables, increase the conduit size by one step. Before pulling, clear the conduit of debris and deburr the ends. Pull at a steady speed, applying talcum powder as a lubricant where needed; never force or jerk the cables. After pulling, leave sufficient spare length at both ends coiled in the junction box, and temporarily seal the conduit ends against dust and cement.
2. Bending
Sizes DN32 and below can be cold bent using a dedicated bending spring; for sizes above DN32, factory-made bends are recommended. Forced bending is prohibited. The bend radius for exposed conduits shall not be less than 6 times the outer diameter; for conduits embedded in concrete, not less than 10 times (GB 50303-2015, JGJ 16). Position the spring at the centre of the bend and apply force slowly and evenly. Heating is not recommended. Avoid multiple bends on the same conduit length.
3. Jointing
Straight joints use dedicated couplers with a socket length of 2–3 times the conduit outer diameter, the conduit ends butting at the socket centre. Clean the joint faces, apply PVC solvent cement evenly, insert with a slight twist and allow to cure without disturbance. Use factory-made 90° or 45° bends for corners and tees for branches. Never substitute hand-bent conduit for a proper bend, and never drill branch holes in fittings. For connection to junction boxes, the insertion depth should be 1.1–1.8 times the conduit outer diameter, secured and sealed with a locknut; add a protective sleeve to exposed sections vulnerable to mechanical damage.
4. Common Mistakes
First, overfilling the conduit - sacrificing heat dissipation, accelerating insulation ageing and preventing future replacement. Second, forced bending - thinning and cracking the wall and creating a short-circuit risk. Third, poor jointing - no cement or sealing, allowing dust and water ingress and reducing protection.
5. Acceptance
Check that the conduit runs are straight and secure with smooth, crack-free bends; joints are firmly cemented with no looseness; after pulling, insulation resistance measured with a 500V megger is not less than 0.5MΩ, with no short or open circuits. Keep a construction record for concealed works and complete acceptance before sealing the chase.
Proper cable pulling, correct bending and reliable joints together form a safe and stable electrical protection system.
