Hitachi NES1-004SB Quick Reference Manual page 15

Chapter 1 Safety Instructions
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 connected 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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