A friend wants to install a tankless water heater under the kitchen sink for faster hot water and plans to use a 40A circuit near the sink that is meant for an electric range. The house was built in the 90s, so the wire to the range is 8/3 with no ground.
The tankless is a pure 240v device and is adamant about requiring a ground, so it requires two hots and a ground. Now, I know that electrically, he has 3 wires available for the device, and the neutral goes to the same place as the grounds. The heater will work, and it should be safe, but is there a reason to not just use the neutral in place of a ground?
Aside from the wire being white instead of green, what are the problems with this install?