Siemens SIMATIC S7-1500 System Manual page 47

Response of the CPU to negative power balance or failure of system power supplies
As soon as a negative power balance/overload is detected by the CPU in a power segment,
the following actions are executed:
● CPU stores the retentive data
● CPU enters the event in the diagnostics buffer
● CPU carries out a restart and repeats this until the cause of the negative power balance
is resolved
Response of the interface m odule to negative power balance or failure of system power supplies
As a result of the overload, the interface module switches off all power segments. The I/O
controller or DP master can no longer access the I/O modules. The interface module
provides diagnostic information and periodically checks the connection to the backplane bus
and re-establishes it.
Exception: In the case of a voltage drop or a hardware fault in power segment 2 or 3, the
corresponding system power supply module switches off its power segment (and possibly
the following segments), and generates a diagnostic alarm, if possible.
More information on the behavior of the system power supply (PS) in the event of a fault can
be found in the manuals for the system power supplies.
Automation system
System Manual, 09/2016, A5E03461182-AD
Application planning
3.4 Power balance calculation
47