Siemens S7-400 Ground Connections, Protective Ground, Device Grounding Method

Wiring the S7-400

4.9Grounding

Introduction

Grounding in accordance with regulations and conscientiously implemented is the prerequisite for proper functioning of a programmable controller.

Each individual component of the S7-400 and of the controlled system must be properly grounded.

Ground Connections

Low-resistance ground connections reduce the risk of electric shock in the event of a short-circuit or faults in the system. Moreover, proper grounding (low-impedance connections: large surface area, wide-area bonding) together with the effective shielding of lines and devices reduces the effect of interference on the system and the interference signal emissions.

Note

Always ensure that operating currents do not flow via ground.

Protective Ground

All equipment of Safety Class I and all large metal parts must be connected to the protective ground. This is essential to ensure that the user of the installation is reliably protected from electric shock.

Furthermore, this serves to discharge interference transferred via external power supply cables, signal cables, or cables to I/O devices.

Shown in Table 4-2 are the grounding methods required for the individual components.

Table 4-2 Methods of Protective Grounding

Device	Grounding Method
Cabinet/frame	Connection to central ground point, e.g. ground bus, via
	cable with protective conductor quality
Racks	Connection to central ground point via cable with
	10 mm2 min. cross-section, when racks are not installed in a
	cabinet and not interconnected via large metal parts
Module	None; automatically grounded via backplane bus when fitted
I/O device	Grounded via power plug
Shields of connecting	Connection to rack or central ground point (avoid ground
cables	loops)
Sensors and actuators	Grounding according to specifications applying to the
	system

Automation System S7-400	Hardware and Installation	4-13
A5E00850741-01