Test 23: Pin Hole Test For Enameled Wire

The intent of this test is to find insulation defects after treatment with a salt water solution.

A wire specimen approximately 1,5 m in length is taken for onductors of nominal diameter less than 0,07 mm, and approximately 6 m in length for conductors of nominal diameter equal to 0,07 mm or more.
For a nominal diameter less than 0,07 mm, 1 m ± 0,05 m of wire shall be wound in a round shape with a diameter of 100 mm ± 50 mm.
For a nominal diameter of 0,07 mm or more, 5 m ± 0,2 m of wire shall be wound in a round shape with a diameter of 300 mm ± 100 mm.

The specimen is placed in an air circulation oven at 125 ºC ± 3 ºC for 10 min (see note 1 below) (if not otherwise specified in the relevant specification). After this heat treatment, without any bending or stretching (see note 2 below), the specimen after cooling to room temperature shall be immersed in an electrolytic solution of sodium
chloride (2 g/l) added with a proper quantity of phenolphthalein  lcohol solution (30 g/l) for the easy evidence of any pin holes
typically pink streams in the solution), with the conductor of
the wire and the solution connected to an electrical circuit with an open-circuit d.c. test voltage of (12 ± 2) V.

The voltage shall be applied for 1 min with the specimen as negative electrode relative to the solution and, in order to avoid excessive heating, the short-circuit current shall be limited to 500 mA.

The number of observed pin holes, without magnification (normal vision), shall be reported.
NOTE 1 Without heat treatment the results cannot be significant.
NOTE 2 Elongation of the wire may lead to the creation of pin holes in the electrolytic solution.
NOTE 3 Because this test is done in an aqueous solution, misleading results may be found for specific enamel types, which show crazing behaviour in water.