Siemens Power Supply Units, An S7-400 Configured with Ungrounded Reference Potential

Wiring the S7-400

4.6Assembling an S7-400 with Ungrounded Reference Potential (Ungrounded Configuration)

Application

In large installations, it may be necessary to configure the S7-400 with an ungrounded reference potential, for example, for ground fault monitoring. This is the case in the chemical industry or in power plants, for example.

Discharge of Interference Currents

With the S7-400 in an ungrounded configuration, any interference currents are discharged to the chassis ground via an RC network integrated in the rack.

Terminal Connection Model

Shown in Figure 4-3 is an S7-400 configured with ungrounded reference potential. In this case you must remove the jumper between reference potential M and the frame element terminal on the rack. The reference potential M of the S7-400 is then connected via the RC network to the chassis ground terminal. When you connect this terminal to the chassis ground, RF interference currents will be discharged and static charges will be avoided.

RC network

Detached jumper

6.8 nF 10 MΩ

M

Frame element terminal

Reference potential M

Chassis ground terminal

Figure 4-3 An S7-400 Configured with Ungrounded Reference Potential

Power Supply Units

When using power supply units, ensure that the secondary winding is not connected to the protective ground conductor.

4-8	Automation System S7-400	Hardware and Installation
		A5E00850741-01