Siemens S5-135U/155U appendix Installation with, Floating Modules, Isolated

Installation Guidelines

Note

For 24 V DC digital output modules with electronic short-circuit protection, you must ensure that the reference potential of the load power supply is connected to terminal L- of the module. If this connection is missing (e.g. open-circuit), a typical current of 15 mA can flow at the outputs. This output circuit is sufficient

Sto prevent energized contactors or relays from being released

Sand to energize high-resistance loads (e.g. miniature relays).

Installation with	With floating modules the control circuit and load circuit are metallically
Floating Modules	isolated.

An arrangement with floating modules is required

Sfor all AC load circuits and

Sfor DC load circuits which cannot be coupled. The reasons are, for example, different reference potentials of the sensors or grounding of the positive terminal of a battery.

Shown in the following figure is a simplified installation with floating modules. The arrangement is independent of the grounding concept. The connections for grounding are therefore not drawn.

			Uint
			Data
			0 V
PS	CPU	DI	DQ
1L+
1L±
PE
24 V DC Control Power Supply
2L+			L1
2L±
			N
24 V DC Load Power Supply			230 V AC Load Power Supply

Figure 3-12 Simplified Representation of an Arrangement with Floating Modules

System Manual	3-27
C79000-G8576-C199-06