Wiring the S7-400
4-3
AutomationSystem S7-400 Hardwareand Installation
A5E00850741-01
4.2 Choosing the Power Supply Module

Estimating the Power Requirement

Youshould make an estimate of the power requirement for each rack of your
S7-400 system in order to select the appropriate power supply module for the rack.
Current consumption and power dissipation of the individual modules can be found
in the relevant data sheets.

Calculation Example

The following modules are to be fitted in a CR with 18 slots:
•1 CPU 414-1
•3 analog input modules SM 431;AI 16 x 16 bits
•5 digital input modules SM 421;DI 32 x 24 VDC
•6 digital input modules SM 422;DO 32 x 24 VDC/0.5A
•1 send IM, IM 460-0
Youcan calculate Current Consumption I in this rack as follows, with the data from
the individual data sheets:
Module Quantity +5VDC (Max. Current Consumption
Values)
I / Module ITotal
CPU 417-4 12600 mA 2600mA
SM 431; AI 16 x 16 bits 3700 mA 2100 mA
SM 421;DI 32 x 24 VDC 530 mA 150 mA
SM 422;DO 32 x 24 VDC/0.5A 6200 mA 1200 mA
IM 460-0 1140 mA 140mA
Tota l 6190 mA
From the data in the table, you can see that you must install a power supply
module PS 407 10A (for connection to 120/230 VAC)or PS 405 10A (for
connection to 24 VDC) in the rack, to cover the current consumption calculated
here.
Note
If you wish to connect an ER to the CR via a send IM with current transfer,you
must also take the current consumption of this ER into account when choosing the
power supply module.