This specification details the criteria for wooden poles deployed in overhead electrical transmission, distribution, and telecom networks within India. It addresses aspects such as timber selection, grading, allowable defects, sizing, species, and preservative processes to guarantee structural integrity, longevity, and safety. The standard is intended for manufacturers, engineers, and utilities aiming for cost-effective and dependable wooden pole solutions compatible with Indian timber varieties and environmental conditions.
Overview
This specification details the criteria for wooden poles deployed in overhead electrical transmission, distribution, and telecom networks within India. It addresses aspects such as timber selection, grading, allowable defects, sizing, species, and preservative processes to guarantee structural integrity, longevity, and safety. The standard is intended for manufacturers, engineers, and utilities aiming for cost-effective and dependable wooden pole solutions compatible with Indian timber varieties and environmental conditions.
Audience
Contents
Structure
Frequently Asked
IS 876 advises selecting timber species based on their modulus of rupture tested on green timber. The classification includes Group A (Very Strong, MOR ≥ 85 N/mm²) such as Sal (Shorea robusta), Group B (Strong, MOR between 65 and 85 N/mm²) like Teak (Tectona grandis), and Group C (Moderately Strong, MOR between 45 and 65 N/mm²) exemplified by Chir (Pinus roxburghii). Proper seasoning and preservative treatments per IS 401:1982 are essential to ensure durability.
Wooden poles are categorized into seven classes according to their ultimate breaking load, tested per IS 1900:1974. Class 1 poles have a breaking load of at least 13,500 N, while Class 7 poles have loads between 3,000 and 4,000 N. Timber species are further grouped into A, B, and C based on bending strength. Minimum ground line circumferences vary by class, timber group, and pole length, with intermediate lengths using the next larger class's circumference.
Only minor insect damage in the form of pinholes up to 100 per 1000 cm² and a maximum concentration of 10 pinholes per 25 cm³ is allowed. Defects such as hollows at the top, cross breaks, and large holes are strictly prohibited. Poles must be free from bark, have flush-dressed branches, and be shaped appropriately at the top. Preservation treatments per IS 401 are required to prevent fungal and insect damage.
Following IS 876, wooden poles must undergo immediate prophylactic treatment after preparation in compliance with IS 401:1982 to prevent insect and fungal attacks. Poles should be stacked on treated crossers at a minimum of 150 mm above ground level in well-drained, debris-free areas. Comprehensive preservative treatment must impregnate the sapwood and as much heartwood as possible, especially for non-durable species, using pressure impregnation methods specified in IS 401.
Poles are assigned to seven classes with minimum circumferences at the ground line position depending on length, timber group, and class. For instance, a 9 m pole in Class 1, Group A requires a minimum circumference of 700 mm at 1.5 m from the butt. The top circumference ranges between 260 mm and 570 mm depending on class. Curvature must be limited within defined tolerances, measured as maximum deviation in one or two planes, ensuring poles remain sufficiently straight for safe installation.
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