It would take a breathtaking crash of 900 points in the Dow Jones industrial average to activate the new circuit breakers at the New York Stock Exchange.

Federal regulators in April approved steeper limits to the point drops that halt trading. The new rules impose 10 percent, 20 percent and 30 percent limits and are recalculated quarterly.A 900-point drop before 2 p.m. would stop trading for an hour. The halt would last 30 minutes if the drop occurred between 2 p.m. and 2:30 p.m. There would be no halt if the 10-percent drop occurred in the last 90 minutes of trading.

The NYSE would halt trading for two hours if the index lost 1,750 points - about 20 percent - before 1 p.m. Trading would stop for an hour if the index lost 1,750 points before 2 p.m., and for the rest of the day if the Dow lost 1,750 points during the last two hours of trading.

A 2,650-point loss at any time would halt trading for the remainder of the day.

Long-standing limits on computer-run program trading kick in when the market swings 50 points in either direction.