Siemens S7-400 installation manual Five Basic Rules for Ensuring Electromagnetic Compatibility

Assembling and Installing Systems

Five Basic Rules for Ensuring Electromagnetic Compatibility

In many cases, you can ensure electromagnetic compatibility by observing the following five basic rules:

Rule 1: Large Area Grounding

When installing the programmable controllers, provide large-area good quality grounding of the inactive metal parts (see Section A.3).

•Make a large-area low-impedance connection of all inactive metal parts to chassis ground.

•For screw connections on painted or anodized metal parts, either use special contact washers or remove the insulating protective layers from the contact points.

•If possible, do not use aluminum parts for grounding. Aluminum oxidizes easily and is therefore less suitable for grounding.

•Make a central connection between chassis ground and the ground/protective ground conductor system.

Rule 2: Correct Cable Routing

Ensure proper routing of lines when wiring (see Sections A.7 and A.8).

•Arrange the cabling in line groups (AC power cables, power supply cables, signal lines, data lines).

•Always install AC power cables and signal or data lines in separate ducts or bunches.

•Route the signal and data lines as closely as possible to grounded surfaces such as cabinet elements, metal bars and cabinet panels.

Rule 3: Secure Cable Shields

Ensure that cable shields are properly secured (see Section 4.9).

•Only use shielded data lines. The shield must have a large-area connection to ground at each end.

•Analog lines must always be shielded. For the transfer of signals with low amplitudes, it may be advisable to connect the shield to ground at only one end.

•Provide the line shields with a large-area connection to a shield/protective ground bar immediately after the cabinet inlet, and secure the shields with cable clamps. Route the grounded shield as far as the module without interruption, but do not ground it there again.

•There must be a low-impedance connection between shield/protective ground bar and cabinet/housing.

•Use metal or metallized connector cases for shielded data lines.

Automation System S7-400	Hardware and Installation	A-7
A5E00850741-01