Asbestos Cement Cable Conduits and Troughs

IS 8870 Scope - Key Dimensions & Specifications

The code covers asbestos cement conduits, troughs, fittings with detailed dimensions and tolerances as per:

1. Asbestos Cement Conduits and Bends (Table 1, Clause 3.1)

• Bends: 90° and 135° angles.

2. Asbestos Cement Troughs (Table 2, Clause 3.2)

3. Conduits with Couplings & Collars (Tables 3 & 4, Clause 3.3)

• Dimensions for conduits, plastic/conical couplings, asbestos cement collars, and rubber rings.
• Shore hardness of rubber rings: 40–50 degrees.

4. Cable Troughs and Accessories (Tables 5-7, Clause 3.3)

• Dimensions for troughs, union clips, and bends.
• Typical bend radius: 100 mm, bend angle: 90°.

Summary Diagram of Components:

graph TD
    A[Asbestos Cement Conduits] --> B[Plastic Couplings]
    A --> C[Conical Couplings]
    A --> D[Asbestos Cement Collars]
    E[Cable Troughs] --> F[Union Clips]
    E --> G[Trough Bends]

Note: All dimensions are in millimeters unless specified. Length tolerances allow

IS 8870: Materials and Manufacture — Key Specifications & Dimensions

1. Asbestos Cement Conduits & Couplings (Clause 3.3)

• Nominal diameters: 50, 80, 100, 125, 150 mm
• Dimensions for conduits with plastic and conical couplings (Table 4):

• Rubber ring Shore hardness: 40 to 50 degrees (for collars)

2. Cable Troughs (Table 5)

IS 8870 - Dimensions and Tolerances Summary

1. Asbestos Cement Conduits & Bends (Table 1, Clause 3.1)

• Bends: 90° and 135° angles.

2. Asbestos Cement Troughs (Table 2, Clause 3.2)

3. Cable Conduits with Plastic &

IS 8870 - Manufacture and Finish: Key Specifications & Tables

1. Manufacture & Finish (Clause 3.4)

• Conduits, troughs, and fittings must conform to dimensional tolerances and finish as per specified tables.
• Troughs must be tested for straightness, thickness uniformity, flexural strength, and water absorption (Clause 5.2).

2. Dimensional Tables (Clause 3.3)

3. Rubber Ring Specification

• Shore hardness: 40 to 50 degrees (for sealing in collars).

Sample Table Extract: Cable Conduit Dimensions (Plastic Coupling)

This ensures uniformity in manufacture and reliable joint sealing for cable conduits and

IS 8870 - Testing Requirements Summary

1. Trough Testing (Clause 5.2 & 6.2.2)

• Tests: Straightness, thickness regularity, flexural strength, water absorption.
• Flexural Strength (Table 11):

• Test Method: Appendix C (flexural test setup).

2. Impact Test for Conduits (Clause 13.4)

• Weight Specs: Cylindrical extension 12 mm long, 13.4 mm diameter.
• Procedure:
  • Weight dropped vertically on sample crest placed in a 120° V-notch on solid plate.
  • Use Table 10 for drop height and initial weight.
  • Increase load gradually to find minimum impact force causing puncture.

3. Dimensions & Tolerances (Clause 3.3)

• Refer to Tables 3 to 7 for detailed dimensions of conduits, troughs, fittings, and clips.

flowchart TD
    A[Trough Sample] --> B{Tests}
    B --> C[Straightness]
    B --> D[Thickness Regularity]
    B --> E[Flexural Strength]
    B --> F[Water Absorption]
    E --> G[Load applied per Table 11]
    H[Conduit Sample] --> I[Impact Test]
    I --> J[Weight drop per Clause 13.4]
    J --> K[Minimum puncture load found]

**Use IS 8870 Appendix C and Tables 10,

IS 8870: Performance Tests Key Formulas & Tables

1. Flexural Strength of Troughs

• Tested as per Appendix C
• Minimum Breaking Load from Table 11 (for free span 1.5 m, load rate 4.5 kN/min):

2. Impact Resistance of Conduits

• Tested as per Appendix A
• Weight with 12 mm length × 13.4 mm diameter dropped from heights in Table 10 on V-notch (120°) support.

• No puncture allowed below these impact forces.

3. Additional Tests on Troughs

• Straightness
• Thickness regularity
• Water absorption

Summary Diagram: Impact Test Setup

flowchart LR
    W[Weight: Cylindrical Extension 12mm × 13.4mm dia]
    H[Drop Height (per Table 10)]
    Vnotch[V-notch (120°) Support]
    Plate[Firm Solid Plate]
    Sample[Sample Trough/Conduit]

    W -->|Dropped from| H --> Vnotch --> Plate --> Sample

Note: Use prescribed load rates and free spans strictly during testing for valid results.

IS 8870: Sampling, Inspection & Testing Summary

Sampling & Inspection (Clause 7.3.1 & 7.1)

• Sampling follows IS 7639-1975.
• Each inspection lot must contain items with identical characteristics.
• Manufacturer performs periodic quality control tests proportional to production volume.
• Maintain certified test records for purchaser inspection.

Key Tables for Dimensions & Tolerances (Clause 3.3)

Example: Cable Conduits with Asbestos Cement Collars (Table 4)

• Rubber ring Shore hardness: 40–50 degrees.

Testing & Inspection Flow (Simplified)

flowchart TD
    A[Production Batch] --> B[Sampling per IS 7639]
    B --> C[Inspection Lot (Uniform Items)]
    C --> D[Quality Control Testing]
    D --> E{Pass?}
    E -- Yes --> F[Record & Certify]
    E -- No --> G[Reject/Rectify]
    F --> H[Inspection by Purchaser]

IS 8870: Marking & Dimensions Summary

Clause 8.1 - Marking Requirements:

• Every conduit and trough must be legibly marked with:
  • Manufacturer's name or trade-mark
  • Nominal size of conduit or trough
  • Relevant IS number (IS 8870)
• Optional: ISI Certification Mark (Clause 8.1.1) indicating compliance and quality assurance.

Key Dimension Tables (Clause 3.3)

Example: Conduit Dimensions with Plastic Coupling (Table 3 excerpt)

Example: Cable Trough Dimensions (Table 5 excerpt)

IS 8870: Impact Resistance Test on Conduits

Key Specifications (Clause 6.1.5 & Appendix A)

• Sample: Minimum 300 mm length conduit section.
• Test Setup:
  • Sample placed on a V-notch (120°) solid support.
  • Weight with cylindrical extension (12 mm long, 13.4 mm diameter) dropped vertically.
• Impact force (N) and drop height (mm) as per nominal diameter (Table 10):

• Procedure:
  • Start with weights below prescribed impact force.
  • Gradually increase load to find minimum force causing puncture.

Test Setup Illustration (Fig. 1):

graph TD
    A[Weight with Cylindrical Extension] -->|Drop Vertically| B[Conduit Sample]
    B --> C[V-notch Support (120°)]
    C --> D[Firm Solid Plate]

This test ensures conduits withstand minimum impact forces without puncture, confirming durability per IS 8870 requirements.

Flattening Resistance Test on Conduits (IS 8870: Clause 6.1.6 & Appendix B)

Key Specifications:

• Sample length: 75 mm ± 3 mm (two samples)
• Load applied: 250 N weight
• Test temperature: 50°C
• Duration: 48 hours under load
• Measurement accuracy: Inside diameter to nearest 0.25 mm before & after test
• Allowable flattening: ≤ 1% reduction in inside diameter

Test Procedure (Appendix B):

1. Cut two ring samples (75 mm length) from conduit.
2. Place samples horizontally, axes parallel on base.
3. Apply 250 N weight bridging both samples (Fig. 2 in IS 8870).
4. Maintain at 50°C for 48 hours.
5. Measure vertical inside diameter before and after loading.

Flattening Percentage Formula:

[ \text{Flattening %} = \frac{D_{\text{original}} - D_{\text{after}}}{D_{\text{original}}} \times 100 ]

• (D_{\text{original}}) = Original inside diameter (vertical)
• (D_{\text{after}}) = Inside diameter after test (vertical)

Acceptance Criteria:

• Flattening percentage must not exceed 1%.

Summary Table:

flowchart LR
    A[Cut 2 samples (75 mm)] --> B[Place horizontally, axes parallel]
    B --> C[Apply 250 N weight bridging samples]
    C --> D[Maintain at 50°C for 48 hours]
    D --> E[Measure inside diameter before & after]
    E --> F[Calculate % flattening]
    F --> G{Flattening ≤ 1%?}
    G -- Yes --> H[Pass]
    G -- No --> I[Fail]

This test ensures conduit maintains shape under load

Flexural Strength Test on Troughs (IS 8870: Clause 6.2.2 & Appendix C)

Key Specifications:

• Free Span: 1.5 m between two hardwood bearers (300 mm long, 75 mm wide, 150 mm deep)
• Load Application Rate: 4.5 kN/min
• Trough Positioning: Base seated on bearers, projecting ≥ 75 mm beyond each bearer

Minimum Permissible Breaking Loads (Table 11):

Apparatus Setup (Clause C-1 & C-2):

• Two hardwood bearers spaced 1.5 m apart on a level base.
• Trough placed perpendicular with base seated on bearers.
• Length of trough extends at least 75 mm beyond each bearer.

Summary Diagram (Loading Arrangement):

graph LR
A[Hardwood Bearer (300mm length)] ---|1.5 m| B[Hardwood Bearer (300mm length)]
C[Trough] -- Positioned at right angles --> A & B
C -- Base seated on --> A & B
C -- Overhang ≥ 75 mm --> A & B

This test ensures troughs meet minimum flexural strength for safe structural performance.