Tensile Test of Conductors

Contents

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Key learnings:

Tensile Test Definition: A tensile test measures the strength of a material by pulling it apart until it breaks.
Purpose of Tensile Test for Conductors: This test ensures that cable conductors, such as aluminium wires, are strong enough to handle the pulling forces they experience during installation and use.
Apparatus for Tensile Test: Essential tools for this test include a tensile testing machine, a plane-faced micrometer, a suitable scale, and a weighing balance.
Procedure of Tensile Test: The conductor specimen is fixed in the machine, and tension is applied gradually until the specimen fractures, noting the breaking load to calculate tensile strength.
Cable Tensile Test: This specific tensile test for cable conductors checks if the material meets the necessary tensile strength requirements for safe and effective use.

The tensile test measures breaking strength of aluminium wires used in electric power cables. IS 10810-2 pulls a specimen to fracture so the conductor grade can be checked against IS 8130. The metal must survive pulling during stranding and laying. Soft copper uses the annealing (elongation) test instead.

Apparatus required for Tensile Test

Tensile Testing Machine: An automatic machine with two end grips that hold the conductor so it cannot slip during the test. The machine must be able to apply the required tension.
A plane-faced micrometer that can read 0.01 mm. Use it to measure the diameter of a circular specimen.
A scale reading to 1 mm, used to measure the length of a shaped solidal specimen.
A balance reading to 0.01 g, used to measure the mass of a shaped solidal specimen.

Method of Tensile Test of Conductors

Take one specimen a little longer than the gauge length. IS 10810-2 uses 250 mm between the marks plus extra at each end for the grips. No special pre-conditioning is required.

Procedure of Tensile Test of Conductors

Measure a circular wire with a plane-faced micrometer. For a shaped solidal conductor, measure mass and length so the area can be calculated. Grip the specimen and raise the load steadily. IS 10810-2 limits jaw separation to 100 mm per minute. Note the breaking load at fracture and divide by the cross-section to get tensile strength in N/mm2. Compare that figure with the IS 8130 minimum for the aluminium grade.