Siemens SIMATIC S7-1500 System Manual page 237

Application planning
6.8 System power supply
Note
Infeed via system power supplies only
To ensure that the power segment overview correctly displays the infeed via the system
power supplies only, you must configure the following option:
1. In STEP 7, open the "Properties" tab of the R/H CPU. Select "System power supply" in the
navigation.
2. Select the option "No connection to supply voltage L+".
Recommended configuration variant with redundant system power supplies and five or
six CPs
In a configuration with five or six CPs, you need to operate the H-CPU additionally externally
via a load current supply. The power fed in from the H-CPU and the two system power
supplies into the active backplane bus must be at least large enough that there is still a
positive power segment overview if a PS fails. The result can be seen in the power segment
overview in STEP 7.
Example: There are six CPs in a configuration variant. With an external supply (e.g. with
PM 70W 120/230V AC), the H-CPU feeds a maximum of 12 W into the active backplane bus.
Two redundant system power supplies PS 25W 24V DC feed 50 W into the power segment.
The active backplane bus and six CPs are supplied (-33.5 W) via the supplied power (62 W). In
the event of a PS (-25 W) or supply voltage failure, the remaining power (62 W - 33.5 W -
25 W = 3.5 W) is still greater than the power drawn. The power balance is positive (+3.5 W).
Note
Infeed via the H-CPU (load current supply) and via the system power supplies
To ensure that the power segment overview correctly displays the infeed via the H-CPU and
via the system power supplies, you must configure the following option:
1. In STEP 7, open the "Properties" tab of the R/H CPU. Select "System power supply" in the
navigation.
2. Select the option "Connection to supply voltage L+".
Power balance check by the CPU for overload
The CPU monitors compliance with a positive power balance:
• At every POWER ON
• At every change of the installed hardware
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S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF