A switchable longitudinal voltage source has a first feed connection for feeding in a first current, a first output connection for outputting the first current, a second feed connection for feeding in a second current, and a second output connection for outputting the second current. An electrical energy store has a first connection and a second connection coupled to the output connections. The switchable longitudinal voltage source further has a center terminal of a first series circuit which directly forms the first output connection or terminal and a center terminal of a second series circuit which directly forms the second output connection or terminal.