KiwiRail is investigating if new overhead lines in Wellington were badly installed and may have been the reason commuter trains ground to a halt for hours in early January.
At the time it said the problem was caused by days of hot weather but also that it was looking into whether there were faulty parts.
Documents released to RNZ under the Official Information Act also reveal heated conversations between KiwiRail staff about the break down.
The company says it is still looking into what happened and a report is due next month.
RNZ reporter Nick James has been looking at the documents.
