Failures of rubber insulation caused by soil microorganisms

THE INVESTIGATION of the cause of the rare failures of nonleaded rubber-insulated cables buried directly in the ground was reported in an earlier paper.¹ These failures were characterized by localized regions of very low insulation resistance. The absorbed water content was no greater than in adjacent regions of high insulation resistance, and the physical properties were usually normal. Drying the failed insulation raised the resistance several decades, but brief exposure to moisture restored the low values. It was suspected that these failures had been caused by soil microorganisms.