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By Michael Mackenzie
The S&P 500 circuit breakers, which began operating this week, were triggered for the first time on Wednesday afternoon when shares in the Washington Post Company doubled in price inside the space of one second.
Shares in the publisher were trading at about $460 at 3.07pm yesterday when an order for 400 shares and 200 shares were both executed at $919.18, followed by 166 shares at $929.18.
These transactions along with various orders of 100, 200 and 500 shares between $456.91 and $462.85 all took place within one second.
The trades were executed on the New York Stock Exchange’s Arca electronic trading platform and they automatically triggered the newly implemented circuit breakers.
Under the new rules, trading in an S&P 500 stock is halted if the price either rises or falls by 10 per cent inside a period of five minutes.
“There was a trading halt of five minutes and it was determined that there was an erroneous print for the 766 shares that traded,” said Ray Pellecchia, spokesman for NYSE Euronext.
“We are waiting to find out what caused the prints,” he added.