Photo: ODT.

Ageing power poles are a multimillion-dollar headache in New Zealand.

Inquiries by ODT Insight have found New Zealand’s 29 lines companies are spending millions dealing with tens of thousands of ageing wooden power poles.

And the companies’ costs are set to rise as more of the poles — some dating back to the 1950s — come up for replacement.

That included Powerco, in the North Island, which is New Zealand’s largest network by area.

Nearly 40,000 of the company’s 265,000 poles were wooden and many were reaching the end of their useful lives, the company’s asset management plan showed.

The network included "significant numbers of defected poles", 11,000 of which needed to be replaced over the next decade, the plan said.

That would require "large investment" covered by Powerco, nearly doubling its capital spending, from $100million a year to $191million a year, by 2021, it said.

But Powerco was not alone, as other lines networks responding to ODT Insight questions detailed their pole replacement plans.

In the South, Aurora has already revealed a $30million plan to accelerate the replacement of almost 3000 poles by the end of next year.

Mainpower planned to spend $3.8million in the next year replacing 500 poles across North Canterbury.

Network Waitaki would spend $1.2million in the same period monitoring and replacing parts of its network, which included about 13,000 wooden poles.

PowerNet, which managed The Power Company, Electricity Invercargill and OtagoNet, would replace 1220 of its 37,535 wooden poles in the next year across Otago and Southland.

Chorus, which took poles with it when it split from Telecom, has spent $33million replacing 16,000 across New Zealand, including 6000 in Otago, in the past five years.

That included poles that had been red-tagged, but figures were not available as the company aimed to replace them within seven days, a spokesman said.

Despite that, Chorus’ spending would ramp up over the next five years, with another $65million earmarked to address the pole problem.

Those problems appeared to be at their worst on Aurora’s network, with more than 1181 "condition zero" red-tagged poles still standing, prompting allegations of network neglect.

But similar concerns have also emerged overseas, including in Australia, where neglected power poles were blamed for starting bushfires that destroyed homes.

The Australian regulator, EnergySafety, found "serious problems" with Western Power’s management of wooden poles in 2005 and 2006, ABC reported.

Two years later, as an audit found the company had "failed to address the critical safety issues" identified, a bush fire that destroyed 38 homes at Toodyay, near Perth, was blamed on a failed pole.

Western Power escaped an EnergySafety prosecution, but still faced civil proceedings and was forced to spend $A620million ($NZ651million) replacing or reinforcing 170,000 power poles.In New Zealand, seven lines companies have together breached quality-price regulations, set by the Commerce Commission, 12 times since 2011.

Written warnings have been issued to three companies — Aurora, Wellington Electricity and Eastland Network — since 2014.

Aurora was warned in 2012, but was already facing a second investigation when the latest power pole concerns prompted fresh investigations by the commission, Energy Safety and Deloitte.

Strata Energy Consulting, which investigated the networks for the commission, also criticised Aurora’s inadequate asset management in a 2013 report.

Strata also found fault with the maintenance practices of Eastland Network, which covered Gisborne, Wairoa and the East Coast, and suggested the ageing state of Wellington Electricity’s network could be partly to blame for storm outages in 2012, 2013 and 2014.

However, all companies contacted insisted they were on top of maintenance, while the Electricity Networks Association said $1.23billion was spent in the year to March 2015 on network assets, including power poles.