KEY POINTS:
An Onehunga community group is challenging a planning decision it says threatens public health by letting Transpower pump too much electricity along overhead power lines to Northland.
Auckland City commissioners have allowed the power grid operator to boost by up to 45 per cent the maximum current it can push along 220,000-volt transmission lines spanning residential, recreational and industrial areas through Onehunga and Mt Roskill.
They said they were satisfied adverse effects would be minor and outweighed by a need to ensure secure supply to North Auckland and Northland until 2013, when Transpower intends having a second high-voltage link in place, possibly running across the harbour bridge and under the Northern Busway.
The six existing lines are carried as two circuits over 92 steel transmission towers between the Otahuhu and Henderson substations, each with a maximum loading which Transpower has until now been allowed to exceed only three times a year.
But the state-owned organisation has won approval, against at least 430 opposing submissions, to exceed the maximum on any one circuit whenever there is a "forced outage" affecting the other.
Although Transpower insists such forced occurrences are rare, the Onehunga Enhancement Society intends appealing to the Environment Court as it says the decision effectively allows the current on each circuit to be increased by 31 per cent on a normal daily basis.
Society chairman Jim Jackson, who owns an electrical manufacturing business beneath the transmission lines, says that is because current can be increased permanently on each circuit to more than half its maximum load without putting Transpower at risk of exceeding the limit when having to double-up in an emergency.
Transpower has also won the right to boost the maximum load by up to 45 per cent for an unlimited number of 15-minute periods.
Mr Jackson, who has refused an offer of $15,000 from Transpower to replace computer screens hampered by interference from the power lines, says no minimum gap has been stipulated between each 15-minute period.
He says the increases in electro-magnetic field strength have long-term health implications for those living and working under the transmission lines - including himself and his 40 staff.
Transpower acknowledged to the commissioners that concentrating electricity current on one set of lines would produce more magnetic radiation. That could create "wobbly or fuzzy" pictures on computers and televisions with cathode ray tubes over an extra 31ha.
But Transpower said the maximum magnetic field would still be only about half the safe radiation limit of 100 microtesla endorsed by the World Health Organisation.
