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Motor-protective circuit-
breaker PKE12 and PKE32
46
06/10 MN03402004Z-DE/EN
The hardware fault tolerance (HFT) for motor-protective
circuit-breaker PKE is 0, since any fault causes the loss of its
safety function. The motor-protective circuit-breaker’s
proportion of non-hazardous faults, which lies between 60
and less than 90 %, yields SIL 2 according to IEC 61508-2,
Table 2.
EN 61508-6 Table C.3 yields a diagnostic coverage of 0.7.
This applies to the CPU of the trip block’s built-in
measurement electronics. The CPU is responsible for
performing the test function, i.e. all input signals from other
components are used for the test function in the CPU. This
lowest diagnostic coverage value has been selected to cover
the worst-case scenario.
Failure rates
• The trip block’s failure rates at 40 °C ambient air
temperature are:
– Failure rate of safe failures
– Failure rate of dangerous failures
– Failure rate of detected safe failures
– Failure rate of dangerous but detected failures
133 FIT = 1.33 x 10
-7
/h
711 FIT = 7.11 x 10
-7
/h
30 FIT = 3 x 10
-8
/h
473 FIT = 4.73 x 10
-7
/h
Summary of Contents for PKE12 Series
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