There was a time when ground pins were not common, and "double insulated" devices were not as common as today. Some of those devices grounded the chassis to th

There was a time when ground pins were not common, and "double insulated" devices were not as common as today. Some of those devices grounded the chassis to the neutral in the receptacle. The only device I know that I've encountered which fit this was the oscilloscope in my high school physics lab. If you plugged it in the wrong way (which could happen but I don't recall how that was possible), and you touched the metal body of the scope, you'd get a little zap out of it.