There are three levels of circuit breaker mechanisms that can trigger a trading halt in the U.S. market:
Level 1: A 7% decline in the S&P 500 Index from the previous day's closing price triggers a 15-minute trading pause.
Level 2: A 13% decline in the S&P 500 Index from the previous day's closing price triggers another 15-minute trading pause.
Level 3: A 20% decline in the S&P 500 Index from the previous day's closing price results in the suspension of trading for the remainder of the day.
It is important to note that Level 1 and Level 2 halts can only occur once per trading day. This means that if the S&P 500 Index falls 7% (leading to a 15-minute pause), trading will only stop again if the decline reaches 13% or more. Similarly, if the S&P 500 Index falls 13% (resulting in another 15-minute pause), trading will only halt again if the decline reaches 20% or more.
For more details, you can refer to this article: https://school.gugu.fund/blog/american-stock-basis/5051242469
Updated