A circuit breaker is a threshold set by a financial exchange to temporarily halt trading when prices decline rapidly in order to prevent panic selling.
Mechanism and application of circuit breakers
Stock exchanges and commodity markets use circuit breakers to pause trading activity when prices drop by a predetermined percentage within a single trading session. These mechanisms give traders time to assimilate information and reassess their positions rather than acting on immediate market momentum. Exchanges establish these parameters to maintain orderly markets and reduce extreme volatility.
Circuit breakers are implemented globally, though the specific trigger levels and duration of the pauses vary by jurisdiction and exchange. The New York Stock Exchange in the United States uses a tiered system based on drops in the S&P 500 index. The Tokyo Stock Exchange in Japan applies static price limits to individual stocks based on the closing price from the previous day. Exchanges in China use a system tied to the CSI 300 Index, though the rules are adjusted based on historical market conditions.
When a benchmark index or individual security hits the designated limit, the exchange suspends trading for a set period. This pause ranges from a few minutes to the remainder of the trading day. During this pause, orders can still be routed to the exchange, but executions do not occur until the halt is lifted.
Example
Imagine a fictional international commodity exchange where traders buy and sell futures contracts for elephant grass. A sudden news report suggests a severe drought will halve the supply of elephant grass across Africa and Asia. Traders begin dumping related agricultural contracts in a panic. This causes the index price of elephant grass futures to plummet by 10 percent within the first hour of trading.
The exchange rules stipulate a circuit breaker at a 10 percent decline. Once the price crosses this threshold, the exchange halts all trading on elephant grass contracts for 15 minutes. During this pause, Elephants trading on the exchange have time to read the actual weather reports and realize the drought predictions were exaggerated. When the exchange lifts the trading halt, the panic has subsided, and the contracts begin trading at a stable price.