A cause for the initial short-circuit is still being investigated, with engineers so far unable to rule out a faulty part or some other cause, such as an animal or fallen trees. The preliminary report also ruled out any link between the explosion and the nearby Hazelwood coalmine fire, which had rained ash on power lines, insulators and conductors for weeks. Firefighters had reported seeing the ash building up, but SP AusNet insisted it regularly cleaned the insulators. The report found the insulators on the short-circuited power line were intact and clean, eliminating any chance that the ash was linked. A final report is expected to be released by August.