Performance of epoxy casting compositions under outdoor weathering at accelerated voltage gradients

A series of epoxy casting compositions was exposed to outdoor weathering while under average voltage gradients of 0.8 and 1.6 kV/in. at five test sites exemplifying a variety of climatic conditions. Performance with respect to tracking and weathering was observed over an eight year period with times under voltage ranging from 40,000 to 60,000 hrs. It was found that bisphenol A epoxies filled with silica perform much better than had been expected, but that performance was upgraded by introduction of alumina trihydrate into the filler system. Introduction of mica or beryl was conducive to severe tracking. Cycloaliphatic epoxies filled with hydrated alumina do not, in general, track under the test conditions used. Hydantoin epoxies, even when filled with silica, have not tracked in exposure times ranging from two to three years. Performance of the test compositions was more erratic at the lower of the two voltage gradients used, but damage at the lower voltage gradient tended to be smaller. Variation in performance with climatic environment was not consistent from composition to composition.