Circuit Breaker

What Is Circuit Breaker?

A circuit breaker is a market safeguard that temporarily halts trading when a stock index falls by a set percentage within a session. The pause is meant to interrupt panic selling, give investors time to absorb information, and let markets restore orderly pricing before trading resumes. Circuit breakers were introduced and later expanded largely in response to the 1987 Black Monday crash, when the Dow Jones Industrial Average fell about 22.6% in a single day — still its largest one-day percentage drop. Under modern U.S. rules descended from those reforms, a Level 1 halt is triggered when the S&P 500 falls 7% intraday.

Why It Matters

Circuit breakers matter as one of the most visible reforms born from a market crash. Black Monday, worsened by automated program trading and portfolio insurance selling, showed how quickly computer-driven orders could overwhelm markets, so regulators built in mandatory pauses. The mechanism was tested dramatically during the 2020 COVID-19 crash, when market-wide circuit breakers were triggered four separate times within about a ten-day span in March, an unprecedented frequency. Supporters say the halts curb disorderly cascades; critics debate whether pauses calm markets or merely delay selling. Either way, circuit breakers embody the lesson that market structure itself can amplify or dampen a crash.

Test Your Knowledge

Questions on this topic from the EconRecall fact bank:

• What market safeguard, which temporarily halts trading after large index declines, was introduced (or significantly expanded) largely in response to the 1987 crash?
  Circuit breakers
• Under the modern market-wide circuit-breaker rules that trace their lineage to reforms following Black Monday, a "Level 1" trading halt is triggered today when the S&P 500 falls what percentage intraday?
  7%
• What October 13, 1989 stock market decline, triggered by the collapse of a proposed leveraged buyout of United Airlines' parent company, tested the circuit-breaker reforms adopted after Black Monday?
  The "Friday the 13th mini-crash" (the Dow fell about 190 points)