Siemens S5-135U/155U appendix Installation of Programmable Controllers for EMC

Installation Guidelines

3.2Installation of Programmable Controllers for EMC

Measures for suppressing interference voltages are often applied only when the control system is already operational and proper reception of a useful signal is impaired. The reason for such interference is usually inadequate reference potentials caused by mistakes in equipment assembly. Described in the following sections are:

SBasic rules for grounding the inactive metal parts

SExamples of cabinet assembly for EMC

SExample of rack and wall mounting for EMC

3.2.1Basic Rules for Assembling and Grounding the Inactive Metal Parts

Ensure wide-area chassis grounding of the inactive metal parts when mounting the equipment. Properly implemented grounding creates a uniform reference potential for the control system, and reduces the effects of picked-up interference.

Chassis grounding is understood to mean the electrical connection of all inactive parts. The entirety of all interconnected inactive parts is the chassis ground.

Inactive parts are conductive parts which are electrically isolated from active parts by basic insulation, and can only develop a voltage in the event of a fault.

The chassis ground must not develop a dangerous touch voltage, even in the event of a fault. The ground must therefore be connected to the protective ground conductor. To prevent ground loops, locally separated ground elements such as cabinets, structural and machine parts, must always be connected to the protective ground system in star configuration.

Ensure the following when chassis grounding:

SConnect the inactive metal parts with the same degree of care as the active parts.

SEnsure low-impedance metal-to-metal connections, e.g. with large-area good quality contact.

SWhen you are incorporating painted or anodized metal parts in the grounding, these insulating protective layers must be penetrated. Use special contact washers or remove the insulating layer.

SProtect the connection points from corrosion, e.g. with grease.

SMovable grounded parts such as cabinet doors must be connected via flexible grounding strips. The grounding strips should be short and have a large surface because the surface is decisive in providing a path to ground for high-frequency interference.

3-8	System Manual
	C79000-G8576-C199-06