SAN FRANCISCO - California businesses braced themselves Thursday for a second consecutive day of rolling blackouts, and the list of banks that were forced to shut down cash terminals or work with customers in the dark continued to grow.

The state's largest banks, Wells Fargo & Co. and Bank of America Corp., had the biggest problems in the power reductions, which hit a smattering of towns and neighborhoods in northern and central California from about 11:30 a.m. to 2:00 p.m. PST Wednesday.

About 100 of Wells' ATMs and 30 of its branches lost power for up to one hour, said spokeswoman Mary Trigg. The bank's data centers have backup generators, she said.

At Bank of America Corp., the state's largest depository institution, 49 ATMs and 12 branches lost power.

Bank representatives said branches stayed open even if they lost power, though customers were unable to complete transactions that used bank computers. In most cases ATMs shut down automatically.

Some companies instituted special security measures. For instance, Washington Mutual Inc., the Seattle thrift company, allowed only one or two customers into branches at a time, said spokeswoman Nova Hunn-Barnett. During Wednesday's outages 16 Wamu branches and 20 ATMs lost power.

Banks are required to have contingency operating plans, said Carol Eckert, a spokeswoman for the Federal Reserve Bank of San Francisco.

Certain locations, such as Bank of the West's branch in Grass Valley, Calif., knew about the blackouts in advance, and some banks had already instituted power-reduction policies. Wells Fargo began to fit its 983 branches with fluorescent fixtures, which it estimates should save $650,000 a year.

California's financial institutions say they expect more blackouts for a day or so.

"We're anticipating that this may continue for a while," said John Stafford, a spokesman for Bank of the West, a BancWest Corp. subsidiary.

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