Shielding cables
Electrical, magnetic or electromagnetic interference fields are weakened and damped by shielding. Interference currents on cable shields are diverted to ground via the shield bus connected conductively to the housing. Ensure that the connection to the protective earth is low-impedance, as the interference currents themselves will otherwise become the interference source.
Observe the following points when shielding cables:
- Only use cables with braided shield.
- The coverage of the braided shield must exceed 80%.
- Always ground the cable shields at both ends of cables. High frequency interference can only be suppressed effectively by grounding cables on both ends.
- Apply the shield to one side only in exceptional cases. In such cases, you will only achieve damping of low frequencies. A shield connection on one side can be more favorable in the following cases:
- An equipotential bonding cable cannot be routed.
- Analog signals (some mV or µA) are transmitted.
- Foil shields (static shields) are used.
- Always use metallic or metalized connectors for signal lines for serial links. Connect the shield of the signal line to the connector housing. Do not connect the shield to pin 1 of the connector strip on an I/O module!
- For stationary operation, we recommend that you fully strip the insulation from the shielded cable and attach it to the shield bus/PE rail.
- Connect the braided shields using metallic cable clamps. The cable clamps must have a large surface contact with the shield.
- Attach the shield of a cable to the shield bus directly where the cable enters the control cabinet.
INFORMATION
- If there is a potential difference between the grounding points, a compensating current can flow through the shield when connected on both sides.
- Ensure adequate equipotential bonding in accordance with relevant VDE regulations in such a case.
