Hitachi WJ200 Series Quick Reference Manual page 99

Important notes
1. Input choke or other equipment is required if necessary to comply with EMC directive
from the harmonic distortion point of view (IEC 61000-3-2 and 4).
2. If the motor cable length exceeds 20m, use output choke to avoid unexpected problem
due to the leakage current from the motor cable (such as malfunction of the thermal
relay, vibration of the motor, etc..).
3. As user you must ensure that the HF (high frequency) impedance between adjustable
frequency inverter, filter, and ground is as small as possible.
 Ensure that the connections are metallic and have the largest possible contact
areas (zinc-plated mounting plates).
4. Avoid conductor loops that act like antennas, especially loops that encompass large
areas.
 Avoid unnecessary conductor loops.
 Avoid parallel arrangement of low-level signal wiring and power-carrying or
noise-prone conductors.
5. Use shielded wiring for the motor cable and all analog and digital control lines.
 Allow the effective shield area of these lines to remain as large as possible; i.e., do
not strip away the shield (screen) further away from the cable end than absolutely
necessary.
 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 ground + PE-potential),
connect the shields of the control lines to ground + PE (protective earth) 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
always must connect to ground + PE at both ends.
 To achieve a large area contact between shield and ground + PE-potential, 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.
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