6. Environmental ageing of insulating materials

The problem of assessing the ageing of solid insulating materials under the effect of environmental stresses, usually encountered in outdoor use, is addressed in French standard NF C 20-540. This standard, which can also be applied to smaller materials, involves the effect of solar radiation and weathering (humidity, rain, heat, cold). The test involves subjecting material specimens to a combined cycle of climatic stresses. Light radiation is produced by a xenon arc lamp combined with quartz and borosilicate glass filters to eliminate wavelengths below 290 nm. The test chamber is shown in figure 35 . The test is carried out on a weekly cycle, the diagram of which is shown in figure 36 .

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