Jan. 5 (Bloomberg) -- Rio Tinto Group, the world’s second- biggest aluminum producer, said a production line at its New Zealand smelter is still closed after a transformer failure in November cut capacity by about 30 percent.

An assessment of the so-called potline at the Tiwai Point plant is continuing and no date has been set for a restart, Diane Collier, spokeswoman for Rio Tinto’s Alcan aluminum unit, said today by telephone from Brisbane. “We are still assessing our options,” she added.

The fault on Nov. 9 shut one of four potlines at the 350,000 metric-ton-a-year smelter, reducing monthly capacity by about 8,500 tons, operator New Zealand Aluminium Smelters Ltd. said Nov. 10.

Tiwai Point, 79 percent-owned by Rio Tinto Alcan, makes the world’s purest aluminum and supplies metal for almost half the hard-drives and capacitors in the world’s computers and LCD screens. Sumitomo Chemical Co. owns the other 21 percent.

To contact the reporter on this story: Brett Foley in Melbourne at bfoley8@bloomberg.net

Last Updated: January 5, 2009 04:12 EST