A protection switching system in a power supply distribution system, comprises at least one protection switch (25) comprising a controllable semiconductor arranged to conduct current through the power supply line in a normal mode, a control unit (27) arranged to place the at least one protection switch in a test mode in which the current is reduced compared to the normal mode, registration means (28, 29) for registering a test mode value of at least one electrical characteristic in the power supply line that will be affected when the test mode is applied, a monitoring unit (30; 47) arranged to evaluate the at least one electrical characteristic and determine, based on the evaluation, whether or not an action should be taken. If a malfunction is detected an alarm is issued to indicate to service personnel that the protection switch should be replaced.