KiwiRail has confirmed warm weather caused the fault which shut down the Wellington region's trains and left some passengers stranded onboard.
On Wednesday afternoon, all rail services in and out of the capital were replaced by buses due to an overhead powerline failure.
Nearly 140 passengers were stuck onboard three trains stopped between stations. For some, it took almost an hour to disembark.
KiwiRail metros general manager Jon Knight said consecutive days of warm weather caused the overhead powerlines to expand.
The faults were related to insulator and weight tension mechanisms, which had exceeded their operating limits and resulted in outages, Knight said.
KiwiRail had rectified all faults, meaning there were no safety risks, but the operator was conducting a full investigation into Wednesday's shut down, he said.
RNZ
