Price Limit Circuit Filter

The Price Limit Circuit Filter (PLCF) is a protective mechanism used by Indian exchanges to curb excessive volatility in exchange‑traded currency derivatives. It defines the maximum price range within which a contract can trade during a session. Understanding PLCF is essential for NISM Series I because questions often test the calculation of price limits and the consequences when the circuit is triggered.

Learning Objectives

1Define Price Limit Circuit Filter and its purpose.
2Explain how price limits are calculated for currency derivatives.
3Describe the circuit‑breaker workflow and its impact on order execution.
4Apply PLCF calculations to typical NISM exam scenarios.

What is the Price Limit Circuit Filter?

The Price Limit Circuit Filter (PLCF) is a rule set by the Securities and Exchange Board of India (SEBI) and implemented by the National Stock Exchange (NSE) and Bombay Stock Exchange (BSE) for all exchange‑traded currency derivatives (ETCDs). Its primary aim is to prevent price manipulation and extreme price swings that could destabilise the underlying foreign‑exchange market.

When a contract’s price moves beyond a pre‑determined band, trading is automatically halted for a short interval (usually 5 minutes). After the pause, the price band is recalibrated based on the last traded price, and trading resumes. This process repeats if the price continues to breach the limits.

For the NISM exam, the PLCF concept appears in multiple choice questions that ask you to identify the correct limit, the duration of a halt, or the sequence of events after a circuit is triggered.

PLCF safeguards market integrity.
It is mandatory for all Indian currency futures and options.

ℹ️Exam Trap – Confusing Settlement Price with Last Traded Price

Students often use the last traded price of the current session to compute the limit. The correct base is the previous day's settlement price (or previous session's closing price for intra‑day contracts). Remember this distinction to avoid a common mistake.

How Price Limits are Determined

The exchange announces a fixed percentage limit for each currency pair, commonly 5% for major pairs like USD/INR and 10% for exotic pairs. The limit is applied symmetrically around the previous settlement price (PSP). The two boundaries are called the Upper Price Limit (UPL) and Lower Price Limit (LPL).

Mathematically, the limits are calculated as:

UPL = PSP × (1 + L%)
LPL = PSP × (1 – L%)

where L% is the price‑limit percentage set by the exchange. If the market price tries to move beyond either boundary, the circuit‑breaker activates.

In practice, the exchange publishes the exact numeric values of UPL and LPL before the market opens, and these values are displayed on the trading screen for participants.

∑Formula: Price Limit Calculation

UPL = P_{S} \times (1 + L) \quad\text{and}\quad LPL = P_{S} \times (1 - L)

Where:

P_{S}= Previous settlement price of the contract in rupees

L= Price‑limit percentage expressed as a decimal (e.g., 5% = 0.05)

UPL= Upper price limit in rupees

LPL= Lower price limit in rupees

Worked Example

Given PSP = 75.00 INR/USD and L = 5% (0.05): Step 1: UPL = 75.00 × (1 + 0.05) = 75.00 × 1.05 = 78.75 Step 2: LPL = 75.00 × (1 - 0.05) = 75.00 × 0.95 = 71.25 Verification: 75.00 × 1.05 = 78.75 and 75.00 × 0.95 = 71.25.

Circuit Breaker Workflow

When the market price reaches either the UPL or LPL, the exchange automatically pauses trading for a pre‑defined interval (normally 5 minutes). During this pause, no new orders are matched, but participants can still modify or cancel pending orders.

After the pause, the exchange recalculates the price band using the last traded price at the moment of the halt. The new UPL and LPL become tighter or looser depending on the direction of the price movement, ensuring that the market does not jump abruptly across a large gap.

If the price breaches the newly set limits again, another halt is triggered. The process can repeat up to three times in a session; after the third halt, trading may be suspended for the remainder of the day for that contract.

Key Stages of the PLCF Circuit Breaker

Stage	Trigger Condition	Action Taken	Duration
Normal Trading	Price within UPL‑LPL band	Orders matched continuously	N/A
First Halt	Price touches UPL or LPL	5‑minute trading pause	5 minutes
Second Halt	Price again reaches new limit	Another 5‑minute pause	5 minutes
Third Halt	Repeated breach	Trading suspended for the day	Rest of session

⚠️Remember the Re‑calibration Rule

After each halt, the price limits are recomputed using the last traded price, not the original settlement price. Forgetting this leads to wrong limit calculations in scenario‑based questions.

Impact on Order Execution and Margin Requirements

During a halt, all pending limit orders that lie outside the newly formed price band are automatically cancelled by the exchange. Market orders are rejected, and traders must re‑submit them after the halt with prices inside the refreshed limits.

Margin requirements may increase temporarily because the exchange perceives higher risk when the price is near a circuit. Participants are required to maintain the stipulated Initial Margin (IM) and Exposure Margin (EM) based on the revised price.

For the exam, remember that a breach of the price limit does NOT change the contract’s lot size or expiry; only the trading window and price band are affected.

Sample Price Movement with PLCF Halts for USD/INR Futures

Exam‑Focused Question Types

Typical NISM questions present a previous settlement price, the applicable limit percentage, and ask you to compute the Upper and Lower Price Limits. Sometimes the question adds a scenario where the market price hits the limit, and you must identify the correct subsequent action (e.g., a 5‑minute halt).

Another common format provides a time‑stamped price series and asks how many halts occurred, or what the revised limits would be after the first halt. These questions test both calculation skill and procedural knowledge.

Key to scoring well is to write down the formula, substitute the numbers carefully, and then interpret the result in the context of the scenario.

Example: NISM‑Style Scenario: Calculating Revised Limits After a Halt

Scenario

The previous settlement price of the EUR/INR futures contract is 88.00 INR. The exchange‑defined price‑limit percentage is 5%. At 10:15 am, the market price reaches 92.40 INR, triggering the first halt. The last traded price before the halt is 92.40 INR.

Solution

Step 1: Compute the initial limits using PSP = 88.00 INR. UPL₁ = 88.00 × (1 + 0.05) = 92.40 INR LPL₁ = 88.00 × (1 – 0.05) = 83.60 INR Since the price touched 92.40 INR, a 5‑minute halt is triggered. After the halt, the exchange recalculates limits using the last traded price (92.40 INR). Step 2: Revised Upper Limit = 92.40 × (1 + 0.05) = 96.02 INR Revised Lower Limit = 92.40 × (1 – 0.05) = 87.78 INR Thus, after the first halt, the new trading band becomes 87.78 – 96.02 INR. Step 3: If the price later reaches 96.10 INR, a second halt would occur because it exceeds the revised UPL.

Conclusion

The example illustrates how limits are recomputed after each halt. Remember to use the last traded price, not the original settlement, for every subsequent calculation.

Common Mistakes to Avoid

Many candidates mistakenly apply the price‑limit percentage to the current market price instead of the previous settlement price. This yields a higher or lower limit and leads to an incorrect answer.

Another frequent error is ignoring the re‑calibration step after a halt. The exam may present a multi‑step scenario; failing to update the base price will produce a wrong second‑level limit.

Finally, some learners forget that the halt duration is fixed (5 minutes) and assume it varies with the magnitude of the breach. The duration is constant across all currency derivative contracts in India.

ℹ️Quick Memory Aid

Remember: "PSP +‑ 5% = Limits, Halt = 5 min, Re‑calc with Last Trade". This three‑part mnemonic helps you answer most PLCF questions.

⭐Exam Takeaways

Price Limit Circuit Filter caps the daily price range of ETCD contracts to protect market stability.
Upper and Lower Limits are calculated using the previous settlement price: UPL = PSP × (1 + L), LPL = PSP × (1 – L).
When price touches a limit, trading halts for 5 minutes; limits are then recomputed using the last traded price.
After each halt, pending orders outside the new band are cancelled and margin may be adjusted.
Common exam trap: using the current market price instead of the previous settlement price for limit calculation.
Mnemonic – "PSP ± 5% = Limits, Halt = 5 min, Re‑calc with Last Trade" aids quick recall.

Practice Questions

8 questions on Price Limit Circuit Filter

What is the primary purpose of the Price Limit Circuit Filter (PLCF) in Indian currency derivatives markets?

When the market price reaches the Upper Price Limit (UPL) or Lower Price Limit (LPL), how long is trading paused?

A USD/INR futures contract has a previous settlement price (PSP) of 80.00 INR and a price‑limit percentage of 5%. What is the Upper Price Limit (UPL)?

After a 5‑minute halt is triggered, which price does the exchange use to recompute the new price band?

For an EUR/INR futures contract, PSP = 88.00 INR and L = 5%. The price reaches 92.40 INR, triggering the first halt. Using the last traded price of 92.40 INR, what is the revised Lower Price Limit (LPL) after the halt?

How many circuit‑breaker halts can occur for a contract in a single trading session before trading is suspended for the remainder of the day?

Which Indian exchanges implement the Price Limit Circuit Filter as mandated by SEBI?

During a 5‑minute halt, what happens to pending limit orders that lie outside the newly formed price band?

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