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 US$460 at 3.07pm yesterday when an order for 400 shares and 200 shares were both executed at US$919.18, followed by 166 shares at US$929.18.

These transactions along with various orders of 100, 200 and 500 shares between US$456.91 and US$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% inside a period of 5 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.

The NYSE finalized its roll-out of the S&P 500 circuit breakers yesterday and the Washington Post Company was included in the last group of companies..—Paul A. Ebeling, Jnr. www.livetradingnews.com

Posted by Shayne Heffernan on Jun 17th, 2010and filed underEquities, Latest News, Markets, USA.You can follow any responses to this entry through theRSS 2.0You can leave a response by filling following comment form or trackback to this entry from your site