After Power Out/On, my S7-400-CPU only starts up, when the power
failure does not exceed a certain duration. The diagnosis buffer
displays an event ID 16#4555 that states that a hot restart is not
possible since the monitoring time limit has been exceeded.
Check the hardware configuration to see if hot restart is
configured as startup option after power on and if a monitoring
time for hot restart has been defined.
Monitoring time means that if the duration of the state Power
off exceeds the time entered in this field the CPU remains in stop
mode and displays above message.
If you do not want to monitor the time, choose the setting "0".
Now the duration of the state power off will not be monitored.
Figure 1: Settings window for configuration of CPU
The numerical value entered is multiplied with factor 100 ms,
which for example results in a monitoring time of 1,2 seconds when
entering a value of 12 (12*100 ms = 1,2 s).