Safety model for electrical equipment

Abstract

A testing procedure is proposed that is based on the dependability, KU, which is defined as the negative logarithm of the safety-specific failure state probability of the safety-relevant components. In order not to exceed a negligibly low risk of accident, the safety-relevant components must have a reliability that increases with the magnitude of the contact voltages or currents. The main task of safety approval is to verify that the dependability of the safety-relevant components meets the specified values. The dependability of the safety-relevant components normally depends on the load. This load can be increased by other components in the failing circuit. Although such critical combinations of such component failures are rare events, they have to be taken into account to a certain degree lest the risk assume inadmissibly high values. In additional test step it is therefore verified that the dependabilities of the individual safety-relevant component do not fall below a specified value. The fact that the KU values of the components must be known does not put additional requirements on the procedure. The proposed procedure is also suitable for safety approval with respect to risk other than electrical shocks, such an excessive heating or flammability.<>