[en] Considerations are made on system redundance in protection systems of the highest class of criteria (class 1, danger of personnel injury) with the result that a 1-out-of-2 closed circuit system is to be preferred to a 2-out-of-3 system. This protecting part may most probably be equally safely constructed from mechanical-hydraulic components as from electro-hydraulic ones. To follow, the criteria classes 2 and 3 are considered which are primarily concerned with the economic aspects. Faults of the 2nd criteria class can be well controlled by 1-out-of-2 open circuit systems, those of 3rd criteria class by 1-out-of-1 open circuit systems. (orig.)