Help me understand the principles behind this:
This means that the branch circuits to the range and dryer will carry current in the neutral (they are 3 wire) and then you are guaranteed to have current in the third uninsulated wire from the sub panel to the main box?
If this is the case, don't you have current in this third wire most of the time anyways from the 110 branch circuits out of the sub panel?
This third wire from the sub to the main panel is not insulated like the other two conductors are. It is bare and just enclosed in the woven fiber looking sheath of this "romex" type cable between the other two conductors. How dangerous is this since this wire is normally carrying current?
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.
Got it. Thanks! It all makes sense now.