A motor-compressor unit for sub-sea applications, comprising: - a pressure casing comprising a motor compartment and a compressor compartment a control system compartment structurally connected to and supported by the pressure casing; - an electric motor housed in the motor compartment formed in the pressure casing; - a compressor housed in the compressor compartment formed in the pressure casing; - a shaft drivingly connecting the electric motor and the compressor; - at least one magnetic bearing (21, 23, 25, 27) rotatingly supporting the shaft; - a control system (37A-37D) for controlling the magnetic bearing (21, 23, 25, 27); wherein the control system (37A-37D) is housed inside said control system compartment; - wherein the pressure casing is comprised of a main casing portion and at least an auxiliary casing portion sealingly connected to one another to form at least a part of the pressure casing; - the control system compartment being arranged in said auxiliary casing portion; and - a partition wall separating the control system compartment from the motor compartment and the compressor compartment; - wherein the partition wall is between the auxiliary casing portion and the main casing portion to sealingly isolate the control system compartment formed in the auxiliary casing portion from the motor compartment and the compressor compartment; - the motor-compressor unit being characterised in that the partition wall comprises first electric connectors on a first surface of the partition wall and second electric connectors on a second surface of the partition wall, the first surface facing the auxiliary casing portion and the second surface facing the main casing portion, each of the first electric connectors being electrically coupled to a respective one of the second electric connectors; and - wherein said partition wall is connected to a cooling medium duct extending therethrough. - a pressure casing comprising a motor compartment and a compressor compartment a control system compartment structurally connected to and supported by the pressure casing; - an electric motor housed in the motor compartment formed in the pressure casing; - a compressor housed in the compressor compartment formed in the pressure casing; - a shaft drivingly connecting the electric motor and the compressor; - at least one magnetic bearing (21, 23, 25, 27) rotatingly supporting the shaft; - a control system (37A-37D) for controlling the magnetic bearing (21, 23, 25, 27); wherein the control system (37A-37D) is housed inside said control system compartment; - wherein the pressure casing is comprised of a main casing portion and at least an auxiliary casing portion sealingly connected to one another to form at least a part of the pressure casing; - the control system compartment being arranged in said auxiliary casing portion; and - a partition wall separating the control system compartment from the motor compartment and the compressor compartment; - wherein the partition wall is between the auxiliary casing portion and the main casing portion to sealingly isolate the control system compartment formed in the auxiliary casing portion from the motor compartment and the compressor compartment; - the motor-compressor unit being characterised in that the partition wall comprises first electric connectors on a first surface of the partition wall and second electric connectors on a second surface of the partition wall, the first surface facing the auxiliary casing portion and the second surface facing the main casing portion, each of the first electric connectors being electrically coupled to a respective one of the second electric connectors; and - wherein said partition wall is connected to a cooling medium duct extending therethrough.