Something that I wondered for a long time is why not just use the neutral to ground the metal case. After all it's at the same potential as ground, right? Why not save copper? There's a good reason of course: if the neutral wire ever gets severed anywhere between the service panel and the appliance, it would cause the appliance case to become live, even without any short anywhere. Like let's say the appliance is a stove, with a heating element between live and neutral. You turn it on, not realizing that the neutral wire is broken; because of that, there's no current through the load, so there's no potential drop across the heating element, so the disconnected neutral line gets energized to live voltage, and if the appliance case is "grounded" by the neutral you get a shock. That's why the appliance case needs its own ground connection independent of the neutral.
![Grounding, Objectionable Current [250.6, 2020 NEC]](/img/n.gif)
Something that I wondered for a long time is why not just use the neutral to ground the metal case. After all it's at the same potential as ground, right? Why not save copper? There's a good reason of course: if the neutral wire ever gets severed anywhere between the service panel and the appliance, it would cause the appliance case to become live, even without any short anywhere. Like let's say the appliance is a stove, with a heating element between live and neutral. You turn it on, not realizing that the neutral wire is broken; because of that, there's no current through the load, so there's no potential drop across the heating element, so the disconnected neutral line gets energized to live voltage, and if the appliance case is "grounded" by the neutral you get a shock. That's why the appliance case needs its own ground connection independent of the neutral.