The invention relates to a current collecting bus-bar comprising electrode housings for accommodating a multiplicity of electrodes in electrical contact therewith. Probes for measuring the electric potential locally established in correspondence of the electrical contacts during the passage of electric current are also connected to the bus-bar. The invention further relates to a permanent monitoring system allowing the continuous evaluation of current distribution on each electrode of electrolysis cells of metal electrowinning or electrorefining plants, connected to an alerting system and to means for disconnecting individual electrodes in case on non-compliance with preset values.