Electricity-PVC-NOTES

Introduction

  • Conduit refers to enclosures for conductors and cables.

  • PVC Rigid Non-metallic Conduit (RNC): Used for over 25 years; lightweight and generally lower in cost compared to steel. And is made up of Combustible Materials.

  • Resists moisture and some corrosive substances but requires an extra bonding conductor to be pulled.

Characteristics of Non-Metallic Conduits

  • Flame retardant: Designed to resist burning.

  • Impact resistance: Not easily damaged by force.

  • Heat resistance: Maintains shape when exposed to heat.

Advantages of PVC Conduits

  • Light in weight

  • Easy to cut and clean

  • Easy to bend

  • Minimal condensation due to low thermal conductivity in the wall of the conduit

  • Cost-effective

  • Excellent electrical and fire-resistant properties

Disadvantages of PVC Conduits

  • Insufficient adhesive

  • Joints may not be waterproof

  • Expands 5 times more than steel

  • Does not provide the same level of mechanical protection as steel

  • Separate circuit protective conductor must be run inside the conduit

Classification of Conduits

  • Asbestos cement conduit

  • Polyvinyl chloride (PVC)

  • High-density polyethylene

Types of Adhesive for PVC

  • Teflon Adhesive: Used when PVC has threads.

  • Solvent Adhesive: Used when PVC does not have threads.

Usage Conditions in the Philippine Electrical Code

  • Rigid non-metallic conduit may be used in:

    • Concealed installations in floors, walls, and ceilings.

    • Direct earth burial conditions with specific depth guidelines.

      • 300 mm below concrete (50 mm thick or equivalent).

      • 600 mm under roads, alleys, driveways, and parking lots.

      • 460 mm under driveways of single and two-family homes.

      • 460 mm under airport runways and nearby areas where trespassing is not allowed.

    • Areas subject to severe corrosive influences.

    • Locations with approved chemicals.

    • Cinder fill or conditions where water entry is controlled.

    • Dry and damp locations.

Prohibited Usage Conditions

  • Hazardous locations

  • Supporting fixtures

  • Areas physically damaged

  • Ambient temperatures above 500°C unless specified.

Installation Requirements

Trimming

  • Trim rough edges from non-metallic conduit ends inside and out.

Joints

  • Use approved couplings and adapters for joints.

  • Use PVC cement for waterproofing.

Supports

  • Rigid non-metallic conduit to be firmly supported based on size and spacing:

    • 15 mm to 25 mm: 900 mm spacing

    • 32 mm to 50 mm: 1500 mm spacing

    • 65 mm to 90 mm: 1800 mm spacing

    • 100 mm to 125 mm: 2100 mm spacing

    • 150 mm: 2400 mm spacing

Expansion Fittings

  • Required for thermal expansion compensation.

Size Limits

  • Minimum size: 15 mm; Maximum: 150 mm.

Bushing

  • This is provided to protect wires from abrasion if the box doesn’t provide

    enough protection.

    It also helps to ensure that the wires do not become damaged during installation or maintenance, thereby enhancing the overall safety and longevity of the electrical system. Additionally, bushings can facilitate smoother wire movement, reducing the risk of wear and tear over time.

Bending Procedures

  • Ensure bends do not damage conduit or reduce internal diameter.

Types of Bends

  1. Elbow Bend

  2. Offset Bend: Less than 90°, used for obstacles.

  3. Round Saddle Bend: Over circular objects.

  4. Square Saddle Bend: For rectangular obstacles, combines two offset bends.

Bend Defects

  • Burned, kinks, or significant reduction of diameter due to improper techniques.

Procedure for Bending PVC Conduit (General Steps)

  1. Prepare tools, materials, and PPE.

  2. Mark right angle for guiding bend on the floor.

  3. Measure distance for elbow mark and apply heat evenly.

  4. Bend conduit when soft and dampen with wet rag to harden.

  5. Perform good housekeeping after work.

Conclusion

  • Follow safety precautions at all times during actual wiring. Reach out for assistance when needed.