Summary Box: SEC issues ‘circuit breaker’ rules aimed to prevent repeat of May 6 stock plunge

Summary Box: SEC puts in new trading halts

NEW RULES IN RESPONSE TO “FLASH CRASH”: The Securities and Exchange Commission has put in new “circuit breaker” rules aimed at preventing a repeat of the May 6 stock market plunge, when the Dow industrials lost nearly 1,000 points in less than a half-hour.

HOW IT WORKS: U.S. stock exchanges will briefly halt trading of some stocks that mark big swings. Trading of any Standard & Poor’s 500 stock that rises or falls 10 percent or more in a five-minute period will be halted for five minutes.

POSSIBLE EXPANSION: The rules will apply for six months. Afterward, their scope could be expanded to securities beyond the S&P 500, including exchange-traded funds.