Expanding powerlines — due to “consecutive days of hot weather” — led to an outage and shut down Wellington’s train lines yesterday afternoon, KiwiRail says.

Thousands of commuters were left stranded yesterday when power outages across the network halted trains. Busses were called in to replace the stopped trains.

This afternoon, KiwiRail’s metros general manager Jon Knight revealed: “Consecutive days of warm weather had caused the overhead power lines that run our passenger trains to expand.”

The faults were related to “insulation and weight tension mechanisms” exceeding limits, resulting in the outages.

KiwiRail has since “rectified all faults” and has deployed standby response crews.

“KiwiRail is conducting a full and detailed technical investigation into the case of the faults, which will take time,” Knight said.

“The network remains fully operational, and there are no safety or compliance risks. It is safe for trains to operate.”

It comes as scorching hot weather has been baking much of the country this weekend.

The city is currently in temperatures of 23C, while rural parts of Wellington, like Lyall Bay, Lower Hutt and Wainuiomata are experiencing 25C heat, according to MetService.

It’s currently 24C in Upper Hutt and 23C in Porirua.