NORD Drivesystems BU0220 - Manual (Page 79)

8 Additional information
BU 0220 GB-0912 Subject to technical amendments 79
8.2 Cable glands and shielding connections
Nowadays, field bus systems are a normal part of plant technology. The sensitivity of these systems to
electromagnetic interference (EMC) means that it is essential to protect bus systems from outside interference
by means of uninterrupted or complete screening. Therefore the use of shielded cables and metal screw
couplings or plug connectors has become standard. Assuming correct installation (e.g.: 360° screen connection
- including at contact points, compliance with tightening torques, bending radii, IP-protection classes (
≥ IP66),…),
the operational reliability of the field bus system can be optimised.
The EMC effect of a cable shield is largely dependent on its contacts to the housing and its earthing on one or
both ends. The shielding effect of a housing must not be influenced by incoming or outgoing screened cables.
It is recommended that the shield is exposed directly at the point of entry and connection of the cable gland
with the reference potential surface and the use of an EMC cable. At the same time this opening in the housing
is "sealed" against the electromagnetic field. The connection from the cable shield to the housing must have a
DC and and inductive resistance which is as low as possible. This depends on the frequency. This low contact
resistance is achieved by the use of a ring-shaped 360° contacting of the cable shielding and short
connections to the housing via the connecting thread.
8.2.1 Fixed connection (cable gland)
Metallic EMC cable glands with a shielding concept should be used to minimise EMC problems.
These special M16 x 1.5 EMC cable glands must be fitted in the relevant connection unit (SK TI4-
…(-BUS)) of the
frequency inverter or the PROFIBUS DP module.
Mounting
For the M16 x 1.5 EMC cable gland, 5 mm of the shielding of the cable /conductor is exposed and slightly
spread out. The insulating foil of the Profibus cable must be cut off and must not be folded back.
Sealing ring
connection
thread
Double
nipple Sealing insert Cable
Cone Shielding mesh Pressure screw
Direction of assembly
Function
When the pressure screw is tightened, the sealing insert presses the shielding mesh onto the cone of the
earthing insert. The entire circumference (360°) of the shielding mesh is contacted. The mesh ends in the
cable gland. This produces a large area, low resistance conductive connection between the shield, the
earthing insert and the screw fitting and the housing.
For further information regarding the correct installation of EMC cable glands, please refer to the relevant
manufacturer´s data sheets.
1 Pressure screw
2 Earthing insert
3 Inner earthing cone
4 Metric fitting
5 O-ring mounted