Auckland's power hangs by a thread

One of the broken earth wires which triggered yesterday's power chaos. Picture / Richard Robinson

National electricity grid operator Transpower was under fire from political, business and civic leaders last night over the huge power cut that brought chaos to Auckland yesterday.

The cause was a small earth wire which a wind gust snapped off a high-voltage pylon near the Otahuhu B substation, short-circuiting lines supplying electricity for 700,000 or more people throughout central, east and southwest Auckland.

Prime Minister Helen Clark was among those who questioned the city's reliance on a single gateway substation between Otara and Otahuhu, saying the Government would seek answers from Transpower.

Four loud bangs heard by road builders several hundred metres away at 8.32am signalled a day of disruption not only to the main 220,000-volt power feed to Auckland's central business district, but also to three of line company Vector's local substations.

The earth wire, designed to protect pylons from lightning strikes, flicked off the main link and on to 110,000-volt switching equipment at Transpower's Auckland gateway substation.

That cut all the substation's output, and also threw the Otahuhu B and Southdown generating stations off the national grid.

A second 220,000-volt line running power to Waitakere, North Shore and Northland was undamaged, letting Transpower feed some load back to central Auckland by late morning, although it took until after 4pm to restore supplies to the rest of the region.

Vector, which receives bulk supply from Transpower, had to take care to restore electricity gradually for safety reasons after separate lines feeding 55,000 customers fell in storm conditions.

'Traffic lunacy' after 300 traffic lights disabled

Commuters faced what the police called "traffic lunacy" after 300 sets of intersection lights were knocked out of action, thousands of workers were left with little to do in darkened offices and factories, shops were shut and university exams cancelled.

Some schools also closed and sent children back early to darkened homes.

Despite some minor collisions and near-hits, the police were thankful nobody was seriously injured in Auckland, although a Chinese sailor was swept off an oil tanker in heavy swells off Wellington as big seas and gales swept up from a snow-blanketed South Island.

Winds also gusted to 80km/h at Auckland Airport and to 130km/h in the outer Hauraki Gulf as contractors scaled the stricken 40m power pylon to secure the two ends of the snapped earth wire.

About 2000 households and businesses also lost power at various times in the Waikato, but lines company WEL Networks said that was from storm damage unrelated to the Transpower disruption.