Raghunathan wrote:

Yes the right way would have been : A.Power down the ...

Ah, the certitude of 20/20 hindsight. There is a principle in physics that unless there is a law prohibiting an event, eventually (given sufficient time) that event will occur. You and/or your co-worker simply fell prey to that law today. There's a saying in this part of the world. If you've never fallen off of a horse, you've never ridden one. I suspect there is an Indian equivalent. No matter what "the right way" might have been, there is no one in this forum who hasn't done something exactly analagous to what you or your coworker tried to do. The only difference is that we haven't slipped yet (or at least not lately).

Moreover, I am more a researcher than an engineer. This means that I think about such problems in much broader strokes. For instance, I use terms like "honking-huge" to describe the capacitance rating of a capacitor. I don't start nailing down part numbers and µFs until much later in the process. This also means that where most people on this forum start out to design a finished project, I start out by doing "proof of principle" tests. And this means that I kluge together "test setups" that would force OSHA (Occupational Safety and Health Administration, government safety inspectors) to shut down a commercial production facility. In other words, I understand perfectly what happened.

In the final analysis, it would be nice to beef up your circuits to withstand such an event. But I think the best advice might have been from the guy who suggested physical dielectric barriers over the 415V terminals. A few boards, however expensive, notwithstanding, this could have been a lot worse if you or the guy had been touching the blade of the screwdriver.