The subject matter of the invention is a terminal block (1) as part of a high or mean voltage plant with at least one converter and at least one transformer, said terminal block (1) comprising several terminal ports (5, 6) disposed side by side, each terminal port (5) having two contacting terminal tongues (5a), an electric circuit being closed by the contacting terminal tongues (5a), there being provided a plug (20) that comprises at least one electrically non conductive plug tongue (22) for disconnecting said terminal tongues (5a) in one terminal port (5) in order to open an electric circuit.