The invention relates to a monitoring system (13) for monitoring electrical devices (A, B, C, D, K) like luminaires. An assignments providing unit (7) provides assignments between the electrical devices and behavior classes defining expected behaviors, wherein a deviation determination unit (9) determines a deviation a) between a monitored behavior of an electrical device assigned to a behavior class and an expected behavior defined by a behavior class and/or b) between a monitored behavior of an electrical device and a monitored behavior of another electrical device, wherein an output unit (10) provides an output depending on the determined deviation. The deviation can be indicative of a commissioning error, i.e., for instance, of an assignment of an electrical device to a wrong room within a building. The monitoring system can therefore allow for an automatic detection of commissioning errors in a building which may have thousands of electrical devices.