Lets say you have copper piping for your water supply and your piping is used as a grounding electrode from your service. Your bare neutral corodes and causes a bad connection back to your service. You touch the frame of your dryer or range and the water pipe at the same time. you then could become a low impedance path back to the main service. Your 120v items do not usually have accessable parts for you to ground yourself out to become that path. At least the ones made today. Hopefully this basic explanation helps.