Monitoring a converter (1) includes detecting whether a value of an input variable (2) for the converter (1) assumes a first prescribed input reference value (41) and checking whether an output variable (3) from the converter (1) likewise assumes a corresponding, second prescribed output reference value (61). This means that the operation of the converter is tested only at occasional instants, specifically only using individual, prescribed values. The fact that only prescribed values (41, 61) are compared with instantaneous values of the input and output variables (2, 3) means that the invention can be implemented using very simple means. The method is particularly suitable for monitoring the operation of a converter (1) in a control or protective device for an electrical switchgear assembly. In this context, when a malfunction in the converter (1) is detected, all protective functions which are dependent on the converter (1) are preferably turned off.