After the overnight plummet in U.S. stock index futures, investors are bracing for potential stock drops Wednesday that could trigger a trading halt.



Marketwide circuit breakers kick in when the falls 7 percent (Level 1), 13 percent (Level 2) and 20 percent (Level 3) from the previous day's close. The S&P closed up 8 points at 2,139.56 on Tuesday.

For Wednesday, Nov. 9, those marketwide circuit breaker levels are:



Level 1, around 1,989.79

Level 2, around 1,861.42

Level 3, around 1,711.65

A U.S. market decline that triggers a Level 1 or Level 2 circuit breaker from the market open at 9:30 a.m., EST, "up to and including" 3:25 p.m. will halt marketwide trading for 15 minutes.

A 20 percent intraday drop at any point in the trading session would trigger a Level 3 circuit breaker and stop market trading for the day.