Calculating Your Power Requirement - Siemens SIMATIC S7 Functional Safety Manual

Fail-Safe CPU and signal module (SM) installation
4.2 Fail-Safe system electrical design rules
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
System components
Total requirements
Current balance
Current balance total
96
5 VDC distributed by
internal bus when
modules are installed
5 VDC CPU loads
5 VDC CPU power
24 VDC distributed by connec-
tion to fail-safe CPU terminals
L+ and M, (identified by arrow
pointing away from the fail-
safe CPU)
Minus
24 VDC CPU loads
Equals
24 VDC CPU power
24 VDC supplied by connection to
external power supply (separate
external supply power budget
required)
24 VDC external power supply
loads
24 VDC external power
S7-1200 Functional Safety Manual
Manual, 02/2015, A5E03470344-AA