In an intelligent centralized control panel, in particular for motors in which case it is known under the name of iMCC, communications with the outside are performed by powerline carrier current or PLC. The wiring of the control panels can thereby be greatly reduced. To enable this type of communication to be used in dense systems containing a large number of line starters and therefore a large number of parallel-connected carrier current interfaces, the invention proposes inserting a preferably electronically adjustable impedance in series with the PLC conversion device. Advantageously, an adjustment algorithm enables the values of the added impedances to be optimized according to the geometry and position of the different interfaces.