An installer was troubled to find that a wire run with numerous LED fixtures was tripping the secondary breaker (retrofit LED MR-16's were used). After spending a lot of time troubleshooting the problem, he found one LED was the culprit. When he removed that one lamp, all the others went back on and the breaker didn't trip. It turned out that the LED had failed and its components shorted out - creating a dead short for the entire wire run. As we know, when incandescents fail, the result is always an open circuit, causing no problems (except for a voltage bump) to the other fixtures. LED's can go either way - they can short and take down an entire system. Not that this is common, but it does happen.