Siemens S5-135U/155U appendix Connecting the Programmable Controller and Load Power, Main Switch

Installation Guidelines

Ratings of Load Power Supplies

Load Power

Supply for

Non-Floating

Modules

Load Power Supply for Floating Modules

The electronic short-circuit protection of digital output modules only responds when 3-times the rated current is exceeded. You should therefore so design the load power supply units that the unit can supply the current required for shutting down in the event of a short-circuit at one output.

In the event of short-circuits at digital outputs, if the load power supply is not adequately rated, a current which is higher than the rated current can flow for a longer period without responding of the electronic short-circuit protection of the DQ module. Operation in the overload region can destroy the module.

If you use non-floating modules, you must create a common reference potential for the internal control circuits of the PLC and for the load circuits. The reference potential of the load power supply should therefore be connected to the ground terminal of the PLC (PE or protective conductor terminal). The ground terminal is permanently connected to the internal reference potential of the controller.

Note

If you use switched-mode power supply units for floating analog modules and BEROs, you must fit an AC system filter to the input of the power supply.

3.4.2Connecting the Programmable Controller and Load Power

Each of the following figures shows a circuit example for connecting the control and load power supplies as well as the grounding concept for operation from:

SGrounded supplies

SCentrally grounded supplies

SUngrounded supplies

When assembling the control system, observe the following explanations.

The text contains identification numbers relating to Figures 3-8 to 3-10.

Main Switch and

ProtectionS For the programmable controller, sensors and actuators, you must fit a main switch À to DIN VDE 0113, Part 1, or an isolating device to DIN VDE 0100, Part 460. If an AC plug is used as the isolating device, the socket must be in the vicinity of the central controller and must be easily accessible (VDE 0805, 1.7.2). These devices are not required in the case of a subsystem where the appropriate devices are fitted at a higher level.

SThe circuits for sensors and actuators can be given group protection for short-circuit and/or overload ￿. According to VDE 0100, Part 725, single-phase protection is required; and all-phase protection to DIN VDE 0113, Part 1.

System Manual	3-21
C79000-G8576-C199-06