Together with the introduction of the floor and ceiling trading limits, SET also implemented a circuit breaker system to curb any excessive volatility in the market that may cause investor panic.
The circuit breaker functions as follows:
First stage: If the SET index falls by 10% from the previous day's close, all trading in listed securities will be halted for 30 minutes.
Second stage: If the SET index falls by 20% from the previous day's close (i.e., another 10%), trading in all listed securities will be halted for one hour.
After second stage, SET will continue matching orders until market close session and no more halted market.
If the trading time remaining in a session is less than 30 minutes or one hour (as the case may be) after the circuit breaker comes into effect, trading will be halted until the closing time of that session, and trading will then resume in the next session.