Circuit Breaker
The index-level safety valve on NSE and BSE that pauses all trading — equities and derivatives — when markets move beyond 10%, 15%, or 20% in a single session.
Definition
A circuit breaker is an exchange-mandated mechanism that automatically halts trading across all segments — equities, futures, and options — when a benchmark index breaches a predefined percentage threshold from its previous day's closing value. In India, the system is co-ordinated between NSE and BSE and is triggered on the higher absolute percentage move of either the Nifty 50 or the Sensex. Circuit breakers apply market-wide and are distinct from individual stock circuit limits (upper and lower circuits), which freeze trading only in a specific security. The mechanism was introduced by SEBI to prevent cascade failures in settlement systems and give participants time to reassess positions during extreme volatility events.
Why it matters
During a circuit breaker halt, no new orders can be placed or modified, and all pending orders are cancelled on resumption (exchanges re-open with a pre-open call auction phase). For F&O traders, this is particularly significant: open interest positions continue to exist but cannot be closed during the halt, meaning hedges cannot be adjusted and delta exposures cannot be managed. Options that were deeply in- or out-of-the-money before the halt can be dramatically re-priced when trading resumes, causing sudden large profits or losses. Traders with naked short positions face the greatest risk, as a violent gap through their strike after the halt reopens can trigger margin calls before they can exit. Understanding circuit breaker conditions is therefore essential for sizing overnight positions responsibly in Indian markets.
How it works
The three-tier system works as follows. A 10% move triggers a 45-minute halt if it occurs before 1:00 PM; a 15-minute halt between 1:00 PM and 2:30 PM; and no halt if after 2:30 PM. A 15% move triggers a 1 hour 45 minute halt before 1:00 PM; a 45-minute halt between 1:00 PM and 2:00 PM; and no halt after 2:00 PM. A 20% move halts trading for the rest of the day regardless of timing. After each halt, markets reopen with a 15-minute pre-open call auction session before normal trading resumes. The thresholds are computed at the beginning of each quarter using the previous quarter's closing index level. Both equity and F&O segments on NSE and BSE are halted simultaneously, as are currency derivatives and any related segments.
Example
Suppose the Nifty 50 closed at 22,000 on the previous day. The circuit breaker thresholds for the next session would be set at approximately 19,800 (10% down), 18,700 (15% down), and 17,600 (20% down), as well as equivalent levels on the upside. If, hypothetically, a major geopolitical event causes Nifty to fall 10% to 19,800 at 11:30 AM, a 45-minute trading halt is triggered. All open orders are cancelled. Markets reopen at 12:15 PM with a 15-minute call auction. A trader who held a short put at 20,000 strike cannot close it during the halt; on resumption, the put's premium may have surged dramatically, requiring immediate attention to manage the position or post additional margin.
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