Wood Poles for Overhead Power And Telecommunication Lines

IS 876: Scope and Key Specifications for Wood Poles

• Scope: Covers wood poles (broad-leaved and coniferous) for overhead power, telephone, and telegraph lines, focusing on strength, durability, size, seasoning, and treatment.

Key Tables & Specifications:

1. Classes of Wood Poles (Table 1)

• Defines Full Length, Ground Line Position, and Minimum Circumference (mm) for 7 classes (Class 1 to Class 7) and groups (A, B, C).
• Example for 6 m pole at 1.2 m ground line:
  • Class 1A: 600 mm circumference
  • Class 3B: 530 mm circumference
  • Class 7C: 410 mm circumference

2. Species of Timber (Annex A)

• Timber grouped into Group A, B, C based on durability and strength.
• Example species & avg. mass at 12% moisture content (kg/m³):
  • Anogeissus latifolia (Axlewood, Group A): 900
  • Dalbergia sissoo (Sissoo, Group B): 770
  • Cedrus deodara (Deodar, Group C): 840

Additional Notes:

• Poles must have square-cut butts and complete bark removal.
• For intermediate lengths, use circumferences of next larger pole class (Clause 5.1.2).
• Refer to IS 401, IS 707, IS 1708, IS 1900 for preservation, terminology, and testing methods.

Summary Table: Minimum Circumference at Ground Line (Example)

This ensures poles meet structural and durability requirements for safe overhead line supports.

IS 876: Key References, Tables & Specifications

1. Species of Timber for Wood Poles (Annex A)

• Timber species are classified into Groups A, B, and C based on durability.
• Average mass at 12% moisture content (kg/m³) is provided for each species.

Note: Non-durable species are marked with (1).

2. Wood Pole Classes & Minimum Circumference (Table 1, Clause 5.1.2)

IS 876 - Definitions & Key Specifications for Wood Poles

1. Curvature Limits (Clause 10.3.10.3):
For poles with double curvature (curvatures in two planes AB and CD), the sum of maximum deviations from tangents in each plane must satisfy:

[ (X_1 + X_2) + (Y_1 + Y_2) \leq \frac{d}{2} ]

• (X_1, X_2): Deviations in plane AB
• (Y_1, Y_2): Deviations in plane CD
• (d): Mean diameter of the pole at the point of maximum deviation

2. Curvature Measurement Planes:

• Plane AB and CD are two planes where curvatures occur, not necessarily perpendicular.
• Deviations are measured from top to bottom convex sides and from ground line to upper convex sides.

3. Pole Classification & Minimum Circumference (Clause 5.1.2 & Table 1):

• For intermediate lengths, use next larger pole circumference.
• Minimum top circumference for all heights ranges from 260 mm to 570 mm depending on class.

4. Other Key Points:

• No splits longer than 600 mm extending across the pole circumference (Clause 10.3.1).
• Butt ends must be sawn square and bark removed.
• Definitions follow IS 707:1976 (Timber glossary).

Summary Diagram: Curvature Measurement

graph TD
  A[Top of

IS 876 - Species of Timber for Wood Poles

Timber Groups by Modulus of Rupture (MoR) (IS 1708:1986)

Key Table: Selected Species & Average Mass at 12% Moisture Content (kg/m³)

Notes:

• Species are classified based on modulus of rupture (bending strength) tested in green condition (>25% moisture).
• Mass values are at 12% moisture content.
• Non-durable species are marked with (1) in the standard.
• Refer Annex A of IS 876 for a comprehensive list.

Summary Diagram: Timber Classification by Strength

graph TD
    A[Group A: Very Strong (MoR ≥ 85 N/mm²)] -->|Example| Sal[Shorea robusta]
    B[Group B: Strong (MoR 65-85 N/mm²)] -->|Example| Teak[Tectona grandis]
    C[Group C: Moderate (MoR 45-65 N/mm²)] -->|Example| Chir[Pinus rox

IS 876: Wood Poles Classification Summary

1. Classification of Wood Poles (Clause 5.1)

• Poles are classified into 7 classes based on ultimate breaking load (tested as per IS 1900:1974):

• Note: Poles with one short crook are downgraded by one class (Clause 5.1.1).

2. Dimensions & Minimum Circumference (Table 1)

• Circumference measured at ground line position varies with pole length and class.
• For intermediate lengths, use circumference of next larger pole length (Clause 5.1.2).
• Example for a 9 m pole at 1.5 m above butt (ground line position):

• Minimum circumference at top for all heights is also specified (e.g., Class 1A = 500 mm).

3. Groups of Timber (Clause 4.2)

• Timber species are categorized into 3 groups (A, B, C) as per Annex A.

Quick Reference Formula for Circumference at Ground Line Position:

For intermediate pole length (L_i):

[ \text{Circumference}{L_i} = \text{Circumference}{L_{next}} \

IS 876: General Requirements for Wood Poles

Key Points from Clause 6 & Table 1 (Classes of Wood Pole)

• Butt Preparation: After felling, poles must have their butts sawn square.
• Bark: Must be completely removed.
• Pole Classification: Based on full length and circumference at specified ground line positions.
• For intermediate lengths: Use circumference values of the next larger pole class (Clause 5.1.2).

Table 1 Summary (Minimum Circumference at Ground Line)

• Minimum Top Circumference: Varies by class, e.g., Class 1A = 500 mm, Class 7A = 260 mm.

Additional Specifications

• Species Suitability: Strength and durability per IS 707:1976.
• Defect Measurement: As per IS 3364 (Part 1):1976.
• Preservation: Follow IS 401:1982 for timber preservation.
• Testing: IS 1708:1986 and IS 1900:1974 for specimen and pole testing.

Summary Diagram: Pole Classification & Preparation Flow

flowchart TD
    A[Felling of Pole] --> B[Butt sawn square]
    B --> C[Bark removal]
    C --> D[Measure circumference at ground line]
    D --> E{Pole length?}
   

IS 876 - Preliminary Treatment of Wood Poles

Key Points from Clause 7 (Preliminary Treatment):

• Poles prepared as per Clause 6 must receive prophylactic treatment immediately to prevent insect and fungal attack.
• Treatment should comply with IS 401:1982 (Code of Practice for Preservation of Timber).
• Treated poles must be stacked on creosoted or treated crossers, at least 150 mm above ground.
• The stacking area must be well-drained and free of wood debris.

Minimum Circumference at Top (Clause 7.5):

• The top of poles shall be leveled in an inverted 'V' shape, length equal to the top diameter or 100 mm, whichever is less.
• Minimum circumferences at the top for all heights are specified in Table 1 (excerpt below):

Table 1 (Minimum Circumference at Ground Line for Various Pole Lengths)

For intermediate lengths, use the next larger pole circumference.

Summary of Preservation Treatment (Clause 8):

• Poles must be treated to impregnate **sapwood and heartwood

IS 876 - Preservative Treatment for Wood Poles

Key Points:

• Preliminary Treatment (Clause 7):

  • Poles prepared as per Clause 6.
  • Prophylactic treatment per IS 401:1982 to prevent insect/fungal damage.
  • Stack poles on treated crossers 150 mm above ground.
  • Ensure proper drainage and cleanliness around stacks.

• Preservative Treatment (Clause 8):

  • Complete impregnation of sapwood and as much heartwood as possible for non-durable species (see Annex A).
  • Treatment pressure and preservative type follow IS 401:1982.

• Species Classification (Annex A):

  • Timber species grouped as Group A, B, C with average mass at 12% moisture.
  • Non-durable species require thorough preservative treatment.

• Marking (Clause 11.1):
  • Each pole marked at 3 m height with:
    • Pole class
    • Timber species symbol
    • Year of preservative treatment

Summary of Treatment Process

flowchart TD
    A[Pole Preparation] --> B[Prophylactic Treatment (IS 401)]
    B --> C[Stacking on Treated Crossers]
    C --> D[Preservative Treatment (Pressure Impregnation)]
    D --> E[Marking & Dispatch]

Reference for Preservative Treatment Pressure (IS 401:1982):

• Typically, pressure treatment involves:
  • Initial vacuum: 0.6–0.8 bar (to remove air)
  • Pressure phase: 7–12 bar (to impregnate preservative)
  • Final vacuum to remove excess preservative.

Note: Always refer to IS 401:1982 for detailed preservative types, concentrations, and pressure cycles.

IS 876: Dimensions and Circumference of Wood Poles

1. Circumference Measurement (Clause 9.2)

• Measured at top and at the ground line position from the butt end.
• Values must comply with Table 1 (see below).

2. Table 1: Minimum Circumferences (in mm)

• Minimum circumference at top for all heights varies from 260 mm (Class 7C) to 570 mm (Class 1A).

3. Intermediate Length Poles (Clause 5.1.2)

• Use circumferences of the **next larger pole

IS 876: Defects Permitted and Prohibited in Wooden Poles

1. Defects Totally Prohibited (Clause 10.2)

• Hollows in the top
• Cross breaks
• Large holes

These defects compromise structural integrity and are not allowed.

2. Defects Permitted to a Limited Extent (Clause 10.3)

• Insect Damage (Clause 10.3.7)
  • Pin holes allowed: up to 100 per 1000 cm²
  • Maximum concentration: 10 pin holes per 25 cm³

3. Measurement of Defects

• Defect measurement as per IS 3364 (Part 1): 1976.

Summary Table for Insect Damage:

flowchart TD
    A[Wooden Pole] --> B{Defects?}
    B -->|Hollows top| C[Rejected]
    B -->|Cross breaks| C
    B -->|Large holes| C
    B -->|Insect damage| D{Pin holes ≤ limits?}
    D -->|Yes| E[Accepted with minor defects]
    D -->|No| C

Note: Always inspect poles visually and measure defects per IS 3364 for compliance.

IS 876 - Marking and Identification of Timber Poles

Key Specifications (Clause 11)

• Location of Marking: At 3 m from the butt of the pole.

• Information to Mark:

  • Class of pole (e.g., Class A, B, etc.)
  • Species of timber by symbol (refer Annex A)
  • Year of preservative treatment

• Butt End Marking (Clause 11.1.1): Class and length of pole, if required by purchaser.

• Standard Mark (Clause 11.2): Poles may carry the BIS Standard Mark, ensuring compliance with IS 876 and quality control.

Annex A: Timber Species Symbols & Average Mass at 12% Moisture Content

(Refer Annex A for full list)

Summary Diagram

graph TD
    A[Timber Pole] --> B[Mark at 3m from Butt]
    B --> C[Class of Pole]
    B --> D[Species Symbol (Annex A)]
    B --> E[Year of Treatment]
    A --> F[Mark Butt End (if required)]
    F --> G[Class & Length]
    A --> H[BIS Standard Mark (Optional)]

Note: Use the species symbol from Annex A for clear identification. The Standard Mark certifies compliance under BIS supervision.

IS 876 - Testing & Quality Control for Wood Poles

Key Points from IS 876:

• Defects Measurement: Per IS 3364 (Part 1):1976, defects in timber are measured and evaluated to classify permissible and prohibited defects (Clause 10.1).

• Shape & Straightness: Clause 10.3.10 emphasizes checking shape and straightness as part of quality control.

• Species Selection: Annex A lists timber species suitable for poles with average mass at 12% moisture content (kg/m³), critical for strength and durability assessment.

Quality Control Specifications:

Defect Measurement Formula (General):

[ \text{Defect Size} = \text{Measured dimension as per IS 3364} ]

• Defects exceeding permissible limits lead to rejection.

Timber Species Mass Example (Annex A):

Summary:

• Ensure shape and straightness comply with Clause 10.3.10.
• Measure defects strictly per IS 3364 (Part 1).
• Use species from Annex A for durability and strength.
• Follow preservation and testing standards (IS 401, 1708, 1900).
• Round off test results per IS 2:1960 rules.

flowchart TD
    A[Wood Pole Sample] --> B{Check Defects}
    B -->|Measure per IS 3364| C{Defect Size}
    C -->|Within Limits| D[Accept Pole]
    C -->|Exceeds Limits| E[Reject Pole]
    D --> F[Check Shape & Straight

IS 876: Species of Timber for Wood Poles

1. Classification of Timber Species (Clause 4.1)

Timber species for poles are classified based on Modulus of Rupture (MOR) of small clear green specimens (moisture > 25%):

2. Annex A (Species List)

• Annex A of IS 876 provides detailed species categorized into these groups.
• Selection depends on strength, durability, and availability.

3. Pole Dimensions & Circumference (Table 1)

• Minimum circumference at ground line varies by pole length, class, and group.
• Example for 9 m pole at 1.5 m from butt:

4. Key Considerations

• Poles must be seasoned and treated per IS 401.
• Butts sawn square, bark removed.
• Use next larger class circumference for intermediate lengths.

Summary Diagram: Timber Strength Classification

graph TD
  A[Group A: MOR ≥ 85 N/mm²] -->|Example| Sal[Sal (Shorea robusta)]
  B[Group B: MOR 65-85 N/mm²] -->|Example| Teak[Teak (Tectona grandis)]
  C[Group C: MOR 45-65 N/mm²] -->|Example| Chir[Chir (Pinus roxburghii)]

For detailed species list and treatment, refer to Annex A and