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With integrated systems (for example, when the adjustable frequency inverter is
communicating with some type of supervisory controller or host computer in the
same control cabinet and they are connected at the same protective ground),
connect the shields of the control lines to protective ground at both ends. With
distributed systems (for example the communicating supervisory controller or host
computer is not in the same control cabinet and there is a distance between the
systems), we recommend connecting the shield of the control lines only at the end
connecting to the adjustable frequency inverter. If possible, route the other end of
the control lines directly to the cable entry section of the supervisory controller or
host computer. The shield conductor of the motor cables must always be
connected to protective ground at both ends.
To achieve a large area contact between shield and protective ground, use a PG
screw with a metallic shell, or use a metallic mounting clip.
Use only cable with braided, tinned copper mesh shield (type “CY”) with 85%
coverage.
The shielding continuity should not be broken at any point in the cable. If the use of
reactors, contactors, terminals, or safety switches in the motor output is necessary,
the unshielded section should be kept as short as possible.
Some motors have a rubber gasket between terminal box and motor housing. Very
often, the terminal boxes, and particularly the threads for the metal PG screw
connections, are painted. Make sure there is always a good metallic connection
between the shielding of the motor cable, the metal PG screw connection, the
terminal box, and the motor housing. If necessary, carefully remove paint between
conducting surfaces.
6.
Take measures to minimize interference that is frequently coupled in through
installation cables.
Separate interfering cables with 0.25m minimum from cables susceptible to
interference. A particularly critical point is laying parallel cables over longer
distances. If two cables intersect (one crosses over the other), the interference is
smallest if they intersect at an angle of 90°. Cables susceptible to interference
should therefore only intersect motor cables, intermediate circuit cables, or the
wiring of a rheostat at right angles and never be laid parallel to them over longer
distances.
7.
Minimize the distance between an interference source and an interference sink
(interference- threatened device), thereby decreasing the effect of the emitted
interference on the interference sink.
You should use only interference-free devices and maintain a minimum distance of
0.25 m from the adjustable frequency inverter.
8.
Follow safety measures in the filter installation.
If using external EMC filter, ensure that the ground terminal (PE) of the filter is
properly connected to the ground terminal of the adjustable frequency inverter. An
HF ground connection via metal contact between the housings of the filter and the
adjustable frequency inverter, or solely via cable shield, is not permitted as a
protective conductor connection. The filter must be solidly and permanently
connected with the ground potential so as to preclude the danger of electric shock
upon touching the filter if a fault occurs.
To achieve a protective ground connection for the filter:
Ground the filter with a conductor of at least 10 mm
2
cross-sectional area.
Connect a second grounding conductor, using a separate grounding terminal
parallel to the protective conductor. (The cross section of each single protective
conductor terminal must be sized for the required nominal load.)
