Circuit Breaker
A safety device that briefly halts the market when prices plunge, to cool overheating and panic — named after an electrical breaker tripping on overload.
In plain terms
When too much electricity suddenly flows, the breaker trips to prevent a fire. A circuit breaker is the same. When prices plunge too fast, it briefly halts trading to prevent the market from collapsing in panic.
In the US, the market halts for 15 minutes each at S&P 500 drops of 7% and 13% in a day, and closes for the day at a 20% drop. It lets the market catch its breath and lets fear settle.
What it tells you
A circuit breaker is "a brake that prevents the market from collapsing in an instant of fear." It gives panicked investors a moment to stop and think.
A circuit breaker triggering signals "the market is plunging at a historically rare pace right now." It is not a common occurrence.
Formula
circuit breaker = a system that temporarily halts trading (or closes for the day) when an index plunges past thresholds (US S&P 500: 7%, 13%, 20%)
What high or low means
A circuit breaker triggering means a phase of severe fear. But whether it falls further or settles after resuming is not set.
On such days volatility (VIX) spikes. The system quells panic, but it does not resolve the root cause of the plunge.
Do not declare "it's the bottom" because a circuit breaker triggered. A halt only buys time; it does not change direction. There have been cases of falling further after resuming.
While trading is halted you cannot buy or sell, so you may not be able to get out when you need to. Along with the system's protection, it is worth knowing this constraint.
In March 2020, as US stocks crashed on COVID-pandemic fear, circuit breakers triggered four times in just ten days. A device almost unused for some 30 years since its 1988 introduction triggered several times in a week.
That is how historic the fear was at the time. Trading halted and resumed several times as the market swung, and it ultimately fell over 30% in about a month. It is a case showing that a circuit breaker can briefly cool panic but cannot stop the plunge itself.
Metrics to read alongside
See it in real stocks
Search US stocks on Stocklore to see Circuit and other financial metrics alongside the sector average.
This explanation is for information and reference only and is not a recommendation to buy or sell any security. Investment decisions and their consequences are your own.