2 Function description
BU 0630 en-2020 25
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2.4.5 Exclusion of wiring faults
In the examples above, a separate shielded cable, with the shield connected at both ends is used for
each of the inputs which are used to implement the safety function (also refer to the following
illustration). These measures are used to rule out faults as per DIN EN ISO 13849-2 in case of a short
circuit between any of the conductors.
This exclusion of faults is necessary in order to fulfil the requirements of safety category 4 as per
DIN EN ISO 13849-1. This means that, neither a single detected fault or an accumulation of
undetected faults can result in the loss of the safety function. A short circuit from an external voltage,
e.g. from a 24V control cable, to the 24V input of a safe shut-down method could lead to the loss of a
safety function I.e. this fault must be prevented by means of suitable measures.
It is not essential to use a separate shielded cable for each input. For example, the cables for the
Safety Digital Input and the Safe Pulse Block may be jointly run in a shielded cable if the monitored
safety outputs of the switching device are equipped with cross-circuit detection (refer to the following
illustration). If necessary, the effectiveness of the cross-circuit detection must be demonstrated.
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