Siemens SIMATIC S7-1500 System Manual page 42

Application planning
3.2 System and load power supply
Infeed via CPU/interface m odule and system power supply
For larger hardware configurations, infeed into the backplane bus by the CPU/interface
module alone no longer suffices. If the modules consume more power in total than the power
supplied by the CPU/interface module, you must insert an additional system power supply.
Supply the system power supply with the permissible supply voltage and the CPU/interface
module with 24 V DC.
Both the system power supply and the CPU/interface module feed current into the backplane
bus. The supplied power is summed.
Power addition: "Infeed power of the system power supply" + "Infeed power of the
CPU/interface module"
Procedure
To set up the supply by means of the CPU/interface module and system power supply,
follow these steps:
1. Open the "Properties" tab of the CPU/interface module in STEP 7 and select the "System
power supply" in the navigation.
2. Select the option "Connection to supply voltage L+".
Figure 3-7
Infeed via system power s upply only
As a further possibility you can supply the required power to the backplane bus using only a
system power supply (in slot 0). In this case, the CPU/interface module is not supplied with
24 V DC, and draws its supply from the backplane bus. The system power supply must be
inserted to the left of the CPU/interface module for this.
In general, you can use system power supplies with AC or DC infeed for the configuration.
If no supply voltage with 24 V DC is present (and e.g. only CMs/CPs are inserted next to the
CPU), you can use a system power supply with 230 V AC because the CMs/CPs are
supplied via the backplane bus.
42
Supply voltage via the CPU/interface module and system power supply
Automation system
System Manual, 09/2016, A5E03461182-AD