Description of device
33
09/15 MN03407003Z-DE/EN
Safety analysis
The following functional safety characteristics were deter-
mined for the motor overload relay ZE/XTOM:
For low demand operating mode with a 1oo1 architecture,
consisting of type A subsystems and a hardware fault toler-
ance (HFT) of 0 (see Table 3 in EN 61508 Part 1 and Table 2
in EN 61508 Part 2) for the overload relays at an ambient
temperature of 50 °C:
Motor protection (overload)
– Safety integrity level
– Safe Failure Fraction (SFF)
– Failure rate for undetected safe failures
(
l
su
)
– Failure rate for detected safe failures
(
l
sd
)
– Failure rate for undetected dangerous failures
(
l
du
)
– Failure rate for detected dangerous failures
(
l
dd
)
SIL 1
89 %
372 x 10
-9
/h
868 x 10
-9
/h
199 x 10
-9
/h
426 x 10
-9
/h
