Siemens Automation System S7-400 - Manual (Page 70)

Wiring the S7-400
4-10
Automation System S7-400 Hardware and Installation
A5E00850741-01
4.7 Assembling an S7-400 with Isolated Modules
Definition
In a configuration with isolated modules, the reference potentials of the control
circuit (M
internal
) and the load circuit (M
external
) are isolated (see also Figure 4-4).
Application
Isolated modules are used for:
• All AC load circuits
• DC load circuits with a separate reference potential
Examples of load circuits with a separate reference potential:
-- DC load circuits whose sensors have different reference potentials (for
example, when grounded sensors are used far from the programmable
controller and equipotential bonding is not possible).
-- DC load circuits whose positive terminal (L+) is grounded (battery circuits).
Isolated Modules and Grounding Concept
You can use isolated modules, regardless of whether or not the reference potential
of the programmable controller is grounded.