PVC Conduits & Cable Trunking — Complete Guide
PVC conduits are rigid or flexible pipes that house and protect electrical wiring inside walls, slabs and surfaces. Cable trunking (and casing-capping) are open channels with removable covers, used for surface wiring where future access matters. Together they form the mechanical protection layer of an electrical installation — shielding copper wires from moisture, impact, rodents and fire spread, while allowing wires to be drawn and re-drawn.
Indian conduits & trunking are governed by IS 9537 (Conduits for Electrical Installations), IS 14927 (Cable Trunking & Ducting) and IS 3419 (Fittings). Major brands: Precision, Polycab, AKG, Astral, Supreme, Finolex, Pressfit, Modi, Plaza Cables, Diamond, V-Guard.
Why Use Conduits?
- Mechanical protection of wires (impact, nails, drilling)
- Protection from moisture & chemical attack
- Protection from rodents & insects
- Fire containment (FR conduit limits flame spread)
- Allows wires to be drawn & replaced without breaking walls
- Neat, organised wiring (especially surface trunking)
- Electrical safety (insulation barrier)
- Code compliance (NEC India / IS 732)
Types of Conduit & Trunking
| Type | Description | Use |
|---|
| Rigid PVC Conduit (Heavy) | Hard straight pipe, high impact | Concealed in slab / wall (heavy duty) |
| Rigid PVC Conduit (Medium / Light) | Standard wall thickness | Concealed wiring in walls |
| Flexible PVC Conduit | Corrugated bendable pipe | Tight bends, machinery, drop ceilings |
| Casing & Capping | U-channel base + snap cover | Surface wiring (renovation) |
| Cable Trunking (Mini / Maxi) | Rectangular duct + removable lid | Surface power/data distribution |
| Floor Trunking | Under-floor cable duct | Offices, large floor plates |
| Skirting Trunking | Decorative skirting-level duct | Offices, labs |
| Cable Tray (perforated) | Metal / FRP open tray | Industrial, basements, services |
| Galvanised (GI) Conduit | Metal conduit | Industrial, fire-critical, exposed |
| HDPE / DWC Duct | Double-wall corrugated | Underground / external cables |
Standard Conduit Sizes (Outer Diameter)
| Size (mm OD) | Inch (nominal) | Typical Use |
|---|
| 20 mm | 1/2" | Lighting / fan points (2–3 wires of 1.5 sq mm) |
| 25 mm | 3/4" | Power sockets (2.5/4 sq mm wires) |
| 32 mm | 1" | Multiple circuits / heavy gauge |
| 40 mm | 1-1/4" | Sub-main feeders |
| 50 mm | 2" | Main risers, multiple sub-mains |
Conduit Fill Rule (IS 732): Total cross-sectional area of all wires should not exceed 40% of the conduit's internal area. Over-filling causes overheating, difficult pulling and insulation damage.
Conduit Grades (Wall Thickness / Impact)
| Grade | Impact Strength | Use |
|---|
| Light Duty | Low (LMS) | Surface, light residential |
| Medium Duty | Medium (MMS) | Concealed residential walls |
| Heavy Duty | High (HMS) | Slab concealing, commercial |
| Extra Heavy Duty | Very high | Industrial, RCC slab |
IS 9537 classifies conduit by mechanical (compression / impact) and thermal (temperature) performance. Use heavy duty for slab concealing where concrete pressure is high.
Conduit Fittings & Accessories
- Bends & Elbows: 90° / 45° direction changes
- Couplers: Join two conduit lengths
- Reducers: Connect different sizes
- Tees: 3-way branching
- Junction / Inspection Boxes: Round / square pull boxes (with covers)
- Saddle / Spacer Clips: Fix conduit to surface
- Glands & Bushes: Cable entry protection
- Deep Concealed Boxes: Modular switch / socket back-boxes
- Flexible Conduit Connectors: Join flexible to rigid
- Adhesive Solvent Cement: Bond joints (rigid)
- Fish / Draw Wire (GI): Pull cables through conduit
Concealed vs Surface Wiring
| Parameter | Concealed Conduit | Surface Casing / Trunking |
|---|
| Aesthetics | Hidden (best) | Visible |
| Installation Stage | During construction | Anytime (renovation friendly) |
| Wire Replacement | Possible (draw through) | Easy (lift cover) |
| Protection | Best (in wall) | Moderate (surface) |
| Future Expansion | Limited | Easy (add channels) |
| Cost | Higher (chasing walls) | Lower |
| Wall Damage | Yes (chasing) | None |
| Use | New homes, premium | Renovation, offices, temporary |
Physical Properties (Rigid PVC Conduit)
| Property | Value |
|---|
| Material | uPVC (unplasticised PVC) |
| Density | 1400 kg/m³ |
| Operating Temperature | −5 to +60 °C |
| Flammability | Self-extinguishing (FR grade) |
| Insulation Resistance | > 100 MΩ |
| Dielectric Strength | > 2000 V (test) |
| Compression Strength | 320–750 N (medium to heavy) |
| Impact Strength | 2–6 J (grade dependent) |
| Standard Length | 3 m per pipe |
| Water Absorption | < 0.5% |
| UV Resistance | Moderate (use UV-stabilised outdoors) |
| Lifespan | 30–40 years |
Top Indian Brands
| Brand | Products |
|---|
| Precision | Precision FR Conduits & Fittings |
| Polycab | Polycab Conduit Pipes & Accessories |
| AKG | AKG FR Conduits, Casing-Capping, Trunking |
| Astral | Astral Conduit (Aquasafe / Electrical) |
| Supreme Industries | Supreme Conduit Pipes |
| Finolex | Finolex Conduit & Fittings |
| Pressfit | Pressfit Conduit, Boxes, Trunking |
| Modi | Modi FR Conduits |
| Plaza Cables | Plaza Conduit & Accessories |
| Diamond / V-Guard | Conduit pipes & casing |
| Legrand / Schneider | Premium trunking & floor systems |
Installation Process (Concealed)
- Mark conduit routes & switch / socket box positions
- Chase (cut grooves) into masonry walls with wall chaser
- Fix concealed back-boxes at correct heights
- Lay conduit in chase / slab; use bends (no sharp kinks)
- Join lengths with couplers + solvent cement
- Secure conduit with saddles / binding wire / nails
- Provide inspection / junction boxes at direction changes
- Insert GI fish wire for later cable pulling
- Plaster over conduit (concealed); cure
- Draw copper wires through after plaster & paint
- Terminate at switches / sockets & DB
Advantages
- Excellent mechanical protection for wires
- Moisture, chemical & corrosion resistant (PVC)
- Rodent & insect protection
- Fire retardant (FR grade) — limits flame spread
- Lightweight & easy to cut / bend
- Non-conductive (electrical safety)
- Allows wire re-drawing without breaking walls
- Economical vs metal conduit
- Wide range of fittings & accessories
- Neat surface trunking for renovation
- Long lifespan (30–40 years)
- No rust (unlike GI conduit)
Disadvantages
- Lower impact strength than GI / metal conduit
- Softens / deforms at high temperature
- UV degradation if exposed (use UV-stabilised outdoors)
- Releases toxic smoke if non-FR PVC burns
- Can crack in very cold conditions
- Not suitable for very high-temperature industrial areas
- Concealed routing makes future re-routing hard
- Over-filling causes wire-pulling problems
- Sharp bends restrict wire pulling
Tests on Conduits
- Compression Test — IS 9537 Part 1
- Impact Resistance Test (at low temperature)
- Bending Test
- Collapse Test
- Flammability / Glow Wire Test — IEC 60695
- Insulation Resistance Test
- Dielectric Strength Test
- Heat Deformation Test
- Dimensional Tolerance Check
- Water Absorption Test
- ISI Mark Verification (IS 9537)
Cost (Approximate, Indian Market, 2025-26)
| Item | Cost |
|---|
| 20 mm Medium Conduit (3 m) | Rs 45 – 75 |
| 25 mm Medium Conduit (3 m) | Rs 70 – 110 |
| 20 mm Heavy Conduit (3 m) | Rs 70 – 110 |
| 25 mm Heavy Conduit (3 m) | Rs 100 – 150 |
| Flexible Conduit (per m) | Rs 12 – 30 |
| Concealed Box (3 module) | Rs 25 – 60 |
| Bend / Coupler / Tee | Rs 8 – 25 each |
| Casing-Capping (per m) | Rs 25 – 70 |
| Mini Trunking (per m) | Rs 40 – 120 |
| Concealed Conduit Wiring (per point, labour+material) | Rs 350 – 700 |
Best Practices
- Use ISI-marked (IS 9537) FR conduit
- Use heavy-duty conduit for slab concealing, medium for walls
- Maintain 40% maximum conduit fill
- Use proper bends — never sharp kinks
- Provide inspection / junction boxes at every direction change
- Keep power and data / signal conduits separate
- Use solvent cement on rigid conduit joints
- Insert GI fish wire before plastering
- Maintain horizontal / vertical conduit runs (no diagonal) for easy fault tracing
- Use UV-stabilised conduit for exterior runs
- Set switch boxes at 1200–1300 mm, sockets at 300–400 mm (or as designed)
- Cap open conduit ends during construction (prevent debris)
- Avoid more than 2 bends between draw boxes
- Use deeper boxes for modular accessories with extra wiring
- Route conduit avoiding plumbing & structural reinforcement
- Document conduit layout drawing for future reference
Applicable Standards
| Standard | Description |
|---|
| IS 9537 (Part 1–5) | Conduits for Electrical Installations |
| IS 14927 (Part 1–2) | Cable Trunking & Ducting Systems |
| IS 3419 | Fittings for Rigid Steel / Non-Metallic Conduits |
| IS 2509 | Rigid Non-Metallic Conduits |
| IS 732 | Code of Practice for Electrical Wiring Installations |
| IS 3837 | Accessories for Rigid Steel Conduits |
| IEC 61386 | Conduit Systems for Cable Management |
| IEC 60695 | Glow Wire / Fire Hazard Testing |
| National Electrical Code (NEC) India 2023 | Electrical Installation Code |
Conclusion
PVC conduits and trunking are the protective skeleton of an electrical installation. For new homes, use ISI-marked FR rigid conduit — medium duty in walls and heavy duty in slabs — with 40% maximum fill, proper bends and inspection boxes. For renovation and offices, surface casing-capping or trunking provides quick, accessible wiring.
Conduits carry copper wires to modular switches & sockets, protected by MCB / RCCB in distribution boards, feeding LED lights and ceiling fans, with a continuous earthing path for safety.