Configuration system for reconfiguring a switch cabinet, comprising: (a) a detection unit configured to detect functional units of an electrical circuit which are mounted within a switch cabinet by way of characteristic features of the functional units, which have unique identifying features which are read out by the detection unit, and the detection unit being formed to detect the electrical circuit implemented by the functional units; (b) a configuration unit including a processor configured to calculate an electrical circuit diagram of the electrical circuit on the basis of the functional units of the electrical circuit which are detected by way of the characteristic features and on the basis of the detected implemented electrical circuit, and automatically to replace the detected functional units of the calculated circuit diagram with associated replacement functional units, which are stored in a database of the configuration system, with a view to at least one optimisation criterion, wherein the optimisation criterion includes: a required installation space of the replacement functional units within the switch cabinet, a development of heat by the replacement functional units within the switch cabinet, a dissipation of heat by the replacement functional units, fulfilment of predetermined certification requirements by the replacement functional units, fulfilment of predetermined power requirements and/or location requirements by the replacement functional units; (c) an output unit configured to output the determined replacement functional units. (a) a detection unit configured to detect functional units of an electrical circuit which are mounted within a switch cabinet by way of characteristic features of the functional units, which have unique identifying features which are read out by the detection unit, and the detection unit being formed to detect the electrical circuit implemented by the functional units; (b) a configuration unit including a processor configured to calculate an electrical circuit diagram of the electrical circuit on the basis of the functional units of the electrical circuit which are detected by way of the characteristic features and on the basis of the detected implemented electrical circuit, and automatically to replace the detected functional units of the calculated circuit diagram with associated replacement functional units, which are stored in a database of the configuration system, with a view to at least one optimisation criterion, wherein the optimisation criterion includes: a required installation space of the replacement functional units within the switch cabinet, a development of heat by the replacement functional units within the switch cabinet, a dissipation of heat by the replacement functional units, fulfilment of predetermined certification requirements by the replacement functional units, fulfilment of predetermined power requirements and/or location requirements by the replacement functional units; a required installation space of the replacement functional units within the switch cabinet, a development of heat by the replacement functional units within the switch cabinet, a dissipation of heat by the replacement functional units, fulfilment of predetermined certification requirements by the replacement functional units, fulfilment of predetermined power requirements and/or location requirements by the replacement functional units; (c) an output unit configured to output the determined replacement functional units.