IEC 60112:2020 pdf free download – Method for the determination of the proof and the comparative tracking indicesof solid insulating materials
4 Principle
The upper surface of the test specimen is supported in a horizontal plane and subjected to anelectrical stress via two electrodes. The surface between the electrodes is subjected to asuccession of drops of electrolyte either until the over-current device operates，or until apersistent flame occurs, or until the test period has elapsed.
The individual tests are of short duration (less than 1 h) with up to 50 or 100 drops of about20 mg of electrolyte falling at 30 s intervals between platinum electrodes, 4 mm apart on thetest specimen surface.
An AC voltage between 100 v and 600 v is applied to the electrodes during the test.
During the test，specimens may also erode or soften，thereby allowing the electrodes topenetrate them. The formation of a hole through the test specimen during a test is to bereported together with the hole depth (test specimen thickness).Retests may be made usingthicker test specimens, up to a maximum of 10 mm.
NOTE The number of drops needed to cause failure by tracking usually increases with decreasing applied voltageand, below a critical value, tracking ceases to occur.For some materials, tracking also ceases to occur above anupper critical value.
5 Test specimen
Any approximately flat surface may be used, provided that the area is sufficient to ensure thatduring the test no liquid flows away from the test electrodes.
NOTE 1ln general flat surfaces of not less than 20 mm × 20 mm are used to reduce the probability of electrolytefiows away from the test electrodes although smaller sizes can be used，subject to no electrolyte loss,e.g.ISo 3i67,15 mm x 15 mm multi-purpose test specimens.
NOTE 2 In general separate test specimens for each test are used. lf several tests are to be made on the sametest piece,testing points can be sufficiently far from each other so that splashes， fumes,or erosion, from thetesting point will not contaminate or influence the other areas to be tested.
The thickness of the test specimen shall be 3 mm or more. Individual pieces of material maybe stacked to obtain the required thickness of at least 3 mm.
NOTE 3 The values of the CTl obtained on specimens with a thickness below 3 mm cannot be comparable withthose obtained on thicker specimens because of greater heat transmission to the glass support through thinner testspecimens. For this reason,stacked specimens are possible.
Test specimens shall have uniformly smooth and untextured surfaces which are free fromsurface imperfections such as scratches, blemishes,impurities，etc,unless otherwise statedin the product standard. lf this is impossible，the results shall be reported together with astatement describing the surface of the specimen because certain characteristics on thesurface of the specimen could add to the dispersion of the results.
For tests on parts of products,where it is impossible to cut a suitable test specimen from apart of a product,specimens cut from moulded plaques of the same insulating material maybe used. in these cases,care should be taken to ensure that both the part and the plaque areproduced by the same fabrication process, resulting in the same surface texture，whereverpossible. Where the details of the final fabrication process are unknown，methods given iniso 293,ISO 294-1 and lSO 294-3 and lSO 295 may be appropriate.