Siemens SIMATIC S7-1200

Fail-Safe CPU and signal module (SM) installation
4.2 Fail-Safe system electrical design rules
S7-1200 Functional Safety Manual
96 Manual, 02/2015, A5E03470344-AA
4.2.2.3
Calculating your power requirement
Form for calculating your power budget
Use the following table to determine how much power (current) is available from the fail-safe
CPU and how much is needed by the central rack modules for your system. Refer to the
technical specifications in this manual for the power ratings of your fail-safe CPU model
(1214FC (Page 149) or 1215FC (Page 160)) and the power requirements of the fail-safe
digital input and output signal modules (SM 1226 F-DI 16 x 24 VDC (Page 172), SM 1226 F-
DQ 4 x 24 VDC (Page 178), or SM 1226 F-DQ 2 x Relay (Page 185)). Refer to the technical
specifications in the S7-1200 Programmable Controller System Manual
(http://support.automation.siemens.com/WW/view/en/91696622) for details about standard
S7-1200 modules.
Table 4- 8 CPU power budget
5 VDC distributed by
internal bus when
modules are installed
24 VDC distributed by connec-
tion to fail-safe CPU terminals
L+ and M, (identified by arrow
pointing away from the fail-
safe CPU)
24 VDC supplied by connection to
external power supply (separate
external supply power budget
required)
Minus
System components
5 VDC CPU loads
24 VDC CPU loads
24 VDC external power supply
loads
Total requirements
Equals
Current balance
5 VDC CPU power
24 VDC CPU power
24 VDC external power
Current balance total