The intent of arc resistance testing is to distinguish between solid electrical insulating materials. It examines the specimen’s ability to resist an arc with high voltage and low current exposed to the material’s insulating surface. The ASTM arc resistance test for dry and uncontaminated materials centers on the time elapsed until tracking paths form.
Arc Resistance Calculation
ASTM-D495 expresses arc resistance as the number of seconds that a material resists forming a surface-conducting path when exposed to a high-voltage, low-current arc occurring intermittently. Results obtained from a nominal 3 mm thickness are meant to represent the material’s reaction in any thickness.
Purpose of the ASTM-D495 Test
Due to its short and convenient duration and use in isolated laboratory conditions, this test method suits:
- Preliminary screening.
- Quality control testing after field experience and other types of simulated service arc tests to establish a correlation.
- Detecting the results of changes in formulation.
Field testing and other simulated service tests should be completed before making any strong conclusions.
Test Procedures for Arc Resistance
Among various materials, ASTM-D495 distinguishes the resistance of a high-voltage, low-current arc close to the insulation surface. The arc forms a conducting path inside the surface of insulation or makes the material become conducting as a result of chemical and thermal erosion and decomposition.
Two electrodes rest on the surface of the material that create an intermittent high-voltage, low-current arc. To distinguish among materials with low arc resistance more easily, this test method’s stages become more severe successively. The earlier stages increase severity by reducing the delay between arc flashes. In the latter stages, increases in arc current represent severity instead.
Four failure types can happen during the test:
- An inorganic compound becomes incandescent and can conduct the arc current, but it reverts to its earlier degree of insulation after cooling.
- An organic compound ignites without an apparent conducting path forming.
- “Tracking” occurs, or a thin and wiry line forms between the electrodes.
- Surface carbonization occurs until there is enough carbon for the current to be carried.
Many materials fail the test within a few seconds of transitioning to the next stage of severity. When comparing arc resistance measurements, time that overlaps two stages have a larger significance than the same amount of time within the same stage.
ASTM-D495 for Arc Resistance of Polymers
While ASTM-D495 evaluates dry, uncontaminated samples, Test Method ASTM D 2132, D 2303, and D 3638 involve wet, contaminated specimens. The ASTM recommends these additional tests for engineering purposes. They should help ASTM-D495 determine some amount of significance for the purposes of quality control.
The ASTM-D495 test does not apply to materials that cannot create a conductive path in response to an electric arc. Materials that form fluid residues or that melt should not be used because they prevent a conductive path from forming.
Arc Resistance Testing From NTS
ASTM standards greatly enhance material performance and create reliable products and equipment. Tests in accordance with ASTM are just a few of the services that NTS engineers perform. Request a quote today for arc resistance testing from NTS. Our team will get in contact to discuss your needs.