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IS 7321:1974 is the Indian Standard (BIS) for selection, handling and erection of concrete poles for overhead power and telecommunication lines. This code provides practical guidance on the selection, handling, transportation, stacking, and erection of both reinforced and prestressed concrete poles. It is intended for poles used in overhead power and telecommunication lines, ensuring their safe installation and structural integrity.
Code of practice for selection, handling and erection of concrete poles for overhead power and telecommunication lines
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! Poles must never be dropped, dragged, or rolled, as this can cause fine cracks that compromise structural integrity. Always use cranes and appropriate slings.
! Ensure backfill around the pole base is compacted in layers to achieve the required stability and prevent leaning.
! Verify pole orientation before erection, especially for poles with pre-drilled holes or a designated weaker axis for stringing.
EN 50341-1:2012CENELEC (European Committee for Electrotechnical Standardization), Europe
HighCurrent
Overhead electrical lines exceeding AC 1 kV - Part 1: General requirements - Common specifications
Covers design and construction of entire overhead line systems, including installation of concrete pole supports.
ASCE/SEI 123-21American Society of Civil Engineers (ASCE), USA
HighCurrent
Prestressed Concrete Transmission Pole Structures
Focuses specifically on prestressed concrete poles, covering design, fabrication, and installation.
IEEE C2-2023Institute of Electrical and Electronics Engineers (IEEE), USA
MediumCurrent
National Electrical Safety Code (NESC)
Provides safety rules for installation of overhead lines, including pole setting depths and foundation requirements (Part 2).
AS/NZS 7000:2016Standards Australia / Standards New Zealand, Australia/New Zealand
MediumCurrent
Overhead line design
Comprehensive design standard that includes requirements and guidance for foundations and erection of line supports.
Key Differences
≠IS 7321 is highly prescriptive, specifying exact concrete mix ratios (e.g., 1:3:6) for backfill, whereas modern standards like EN 50341 specify performance requirements (e.g., a minimum compressive strength like C20/25).
≠The Indian standard from 1974 contains minimal safety guidance. In contrast, standards like IEEE C2 (NESC) provide extensive, legally mandated safety protocols for site work, equipment operation, and working near energized components.
≠IS 7321 primarily covers traditional compacted soil or simple concrete backfills. International standards like ASCE 123 address a wider range of modern foundation options, including drilled piers, direct embedment with engineered backfill, and require more detailed geotechnical analysis.
≠IS 7321 does not provide a specific numerical tolerance for pole verticality (plumbness), stating only that it 'shall be made plumb'. International codes typically specify a maximum deviation, such as a ratio (e.g., 1:300) or a value per meter of height.
Key Similarities
≈All standards emphasize the fundamental need to avoid shock loads, dropping, or impact damage during handling and transportation to prevent micro-cracking and structural failure.
≈The basic erection sequence of excavation, pole lifting, setting, plumbing (ensuring verticality), and backfilling is a common procedural framework across all standards.
≈Both IS 7321 and international counterparts stress the importance of proper storage on level bearers (dunnage) at specified support points to prevent damage from excessive bending stresses.
≈There is a shared understanding that proper compaction of the backfill material around the pole base is critical for the structure's long-term stability and to prevent leaning.
Parameter Comparison
Parameter
IS Value
International
Source
Pole Planting Depth
Normally one-sixth of the total length of the pole.
Performance-based; typically defined as a percentage of the above-ground height plus a fixed depth (e.g., 10% of height + 0.6m), subject to engineering analysis of soil and load conditions.
IEEE C2
Backfill Concrete Mix
Prescribed nominal mix of 1:3:6 (cement:sand:aggregate).
Performance-based; specifies a minimum 28-day compressive strength (e.g., 20 MPa or 3000 psi) based on foundation design.
ASCE 123
Curing Time Before Loading (Concrete Backfill)
Minimum of 7 days before any work is carried out on the pole.
Permissible after concrete reaches a specified percentage of its design strength (e.g., 75%), confirmed by testing; time may vary.
ASCE 123
Lifting Method
At points marked by manufacturer, or if not marked, at 1/5th length from each end.
Strictly at designated pick-up points marked on the pole by the manufacturer, which are determined by design calculations.
ASCE 123
Pole Stacking Height
Tier height should not exceed 4 or 5 poles.
Varies by manufacturer, but generally limited to prevent damage to lower poles; focus is on using proper dunnage at designated points.
ASCE 123
Verticality Tolerance (Plumbness)
Not numerically specified; pole 'shall be made plumb'.
Specified as a ratio (e.g., 1:300) or max deviation (e.g., < 25 mm in 3 m).
EN 50341-1 (via National Annexes)
⚠ Verify details from original standards before use
Key Values4
Quick Reference Values
Typical setting depth for poles in normal soil1/6th of the overall length of the pole
Recommended minimum distance of sling from pole end for lifting0.2 times the overall length of the pole
Maximum recommended stacking height1.5 meters or 5 layers
Maximum overhang during transportNot to exceed 1/3rd the length of the pole beyond the vehicle's body
What is the standard method for unloading concrete poles?+
Poles should be unloaded using a crane or derrick with suitable slings. Dropping or uncontrolled rolling is strictly prohibited. (Clause 4.1)
What is the recommended setting depth for a concrete pole in the ground?+
In normal soils, the setting depth should generally be 1/6th of the pole's overall length. This may need to be increased in poor soil conditions. (Clause 5.4)
How should concrete poles be stacked at a storage site?+
Stack them horizontally on firm, level ground using wooden bearers. Stacks should not exceed 1.5 m or 5 layers in height. (Clause 4.2)
Where should slings be placed for lifting a pole?+
For a single-point lift, the sling should be at the center of gravity. For a two-point lift, slings should be placed at approximately 0.2 times the pole length from each end. (Clause 4.1.2)