Siemens S7-400 Choosing the Load Current Power Supply, Load Current Power Supplies

Wiring the S7-400

4.3Choosing the Load Current Power Supply

Choosing the Load Current Power Supply

The input and output circuits (load current circuits) as well as sensors and actuators are powered by the load current power supply. Listed in the following are the characteristics of the load current power supplies required in special applications for choosing the load current power supplies.

Characteristics of	Required for ...	Remarks
the Load Current
Power Supply
Safe isolation	Modules which must be	The Siemens SITOP power load current
	supplied with voltages	supplies have this characteristic.
	≤ 60 VDC
	or ≤ 25 VAC.
	24 VDC load circuits
Tolerances of the		If the output voltage tolerances are
output voltages:		exceeded, you should provide an energy
20.4 V to 28.8 V	24 VDC load circuits	storage capacitor. Rating: 200 μF per 1 A
40.8 V to 57.6 V	48 VDC load circuits	load current (with bridge rectification).
51 V to 72 V	60 VDC load circuits

Load Current Power Supplies

The DC load current power supply must meet the following requirements:

Only a safe, isolated extra-low voltage of ≤ 60 VDC may be used as the load current supply. Isolation may be implemented according to the requirements of the following, amongst other publications:

VDE 0100-410 / HD 384-4-41 S2 / IEC 60364-4-41 (as a functional extra-low voltage with isolation) or VDE 0805 / EN 60950 / IEC 60950

(as a safety extra-low voltage SELV) or VDE 0106 Part 101.

Determining the Load Current

The required output load current is determined by the accumulated current of all sensors and actuators connected to the outputs.

IN the case of a short-circuit, a current of two to three times the rated output current flows briefly at DC outputs before the switched electronic short-circuit protection becomes effective. When selecting the load current power supply, therefore, you must ensure that the increased short-circuit current is available. With unregulated load current power supplies, this excess current is generally ensured. With regulated load current power supplies, particularly at low output levels (up to 20 A), you must ensure a suitable excess current.

4-4	Automation System S7-400	Hardware and Installation
		A5E00850741-01