I had posted this question before, but never received an answer, so I deleted it and reposted a more complete question.
These are the three wires that go into a 240v Stiebel Eltron DHC 6-2 Electric Tankless Water Heater. Even though it's 240v, one of the things the electrician told me when he installed it was that the heater wouldn’t heat the water as well because the existing connection’s 120v. The breaker is two-pole.
With that wiring I want to install a regular outlet from this installation. This is the link to the Leviton outlet I'll be buying at home depot.
Three wires go into the heater, but I'm not sure what the 3rd wire is (the one without the plastic cover)
Any help is appreciated.