In England we have to have our machines PAT tested by a qualified electrician so that we can take them to workshops etc. One of them told us that the machines are usually fine, but the testing is more for the foot pedals as that's where the problems usually begin. I've known a couple of instacnes where the foot pedal can burst into flames. We were advised to also unplug our machines from the socket, not just switch off the the switch on the wall, so that if there is a power surge your machine is protected.