A maintenance technician at an Ausgrid facility in a Canterbury substation is suspected of causing the power blackout that struck large parts of Sydney on Thursday afternoon, closing roads and rail lines and triggering another peak hour nightmare for tens of thousands of commuters.
The fault at the Canterbury subtransmission substation occurred at 4.35pm, at the same time an Ausgrid employee was conducting what a spokesman described as ''urgent'' but unrelated maintenance work.
The fault caused a power outage that shut electricity to about 60,000 homes and businesses in the inner west and inner south, suspended services on the Bankstown train line and closed the M5 tunnels at peak hour.
It was not until about 6.20pm that both eastbound and westbound M5 tunnels had reopened and by then traffic had banked up deep into the city.
The Bankstown line did not reopen until 6.45pm, by which time crowds at Sydenham station had become so crushing the Transport Management Centre was advising people to avoid the area.
The failure was the second peak-hour collapse in Sydney's public transport network this week. On Tuesday afternoon, train signals broke down at Wynyard station, prompting delays of up to an hour for commuters travelling home on the Western and Northern lines.
An Ausgrid spokesman said: ''Given that a technician was on site where we know the fault occurred, we do suspect there is a link between his work and the interruption.
''But we want to make sure we conduct a full investigation,'' he said.
The fault at Canterbury caused power to be cut from three Ausgrid ''zone'' substations, affecting a large swath of the inner west roughly bordered by Petersham, Ashfield, Earlwood, Belmore and Enfield.
Power was restored to homes and businesses about 5.20pm, but it took longer to reboot the safety systems in the M5 tunnels and to restore power along the Bankstown line's substations.
Waiting at Redfern station just before 6pm, Greg Paterson said he had been delayed by 25 minutes after his train to Dulwich Hill was forced to stop early at Sydenham.
''You just come to expect it,'' Mr Paterson said. ''That's just Sydney trains.''
At Sydenham almost an hour later, Lisa Cumming from Bankstown was waiting in the cold at a bus stop long after she should have been home. ''All up I reckon it'll be a two-hour delay,'' she said.
''There was just a sea of people, it was amazing,'' she said of the overcrowded station.
The breakdown in public transport opened opportunities for taxi drivers, but they also found the situation difficult.
''It's great business but I can't move anywhere,'' cab driver George Tannous said. ''I'm like a fox who can't get in the garden.''