74
Unidrive M Modular Installation Guide
Issue Number: 2
Figure 6-23 Grounding of signal cable shields using the
grounding bracket
6.10.6 Variations in the EMC wiring
Interruptions to the motor cable
The motor cable should ideally be a single length of shielded or armored
cable having no interruptions. In some situations it may be necessary to
interrupt the cable, as in the following examples:
•
Connecting the motor cable to a terminal block in the drive enclosure
•
Installing a motor isolator/disconnect switch for safety when work is
done on the motor
In these cases the following guidelines should be followed.
Terminal block in the enclosure
The motor cable shields should be bonded to the back-plate using
uninsulated metal cable-clamps which should be positioned as close as
possible to the terminal block. Keep the length of power conductors to a
minimum and ensure that all sensitive equipment and circuits are at
least 0.3m (12 in) away from the terminal block.
Figure 6-24 Connecting the motor cable to a terminal block in the
enclosure
Using a motor isolator/disconnect-switch
The motor cable shields should be connected by a very short conductor
having a low inductance. The use of a flat metal coupling-bar is
recommended; conventional wire is not suitable.
The shields should be bonded directly to the coupling-bar using
uninsulated metal cable-clamps. Keep the length of the exposed power
conductors to a minimum and ensure that all sensitive equipment and
circuits are at least 0.3 m (12 in) away.
The coupling-bar may be grounded to a known low-impedance ground
nearby, for example a large metallic structure which is connected closely
to the drive ground.
Figure 6-25 Connecting the motor cable to an isolator/disconnect
switch
Surge immunity of control circuits - long cables and
connections outside a building
The input/output ports for the control circuits are designed for general
use within machines and small systems without any special precautions.
These circuits meet the requirements of EN 61000-6-2:2005 (1 kV
surge) provided the 0 V connection is not grounded.
In applications where they may be exposed to high-energy voltage
surges, some special measures may be required to prevent malfunction
or damage. Surges may be caused by lightning or severe power faults in
association with grounding arrangements which permit high transient
voltages between nominally grounded points. This is a particular risk
where the circuits extend outside the protection of a building.
As a general rule, if the circuits are to pass outside the building where
the drive is located, or if cable runs within a building exceed 30 m, some
additional precautions are advisable. One of the following techniques
should be used:
1.
Galvanic isolation, i.e. do not connect the control 0 V terminal to
ground. Avoid loops in the control wiring, i.e. ensure every control
wire is accompanied by its return (0 V) wire.
2. Shielded cable with additional power ground bonding. The cable
shield may be connected to ground at both ends, but in addition the
ground conductors at both ends of the cable must be bonded
together by a power ground cable (equipotential bonding cable) with
cross-sectional area of at least 10 mm
2
, or 10 times the area of the
signal cable shield, or to suit the electrical safety requirements of the
plant. This ensures that fault or surge current passes mainly through
the ground cable and not in the signal cable shield. If the building or
plant has a well-designed common bonded network this precaution
is not necessary.
3. Additional over-voltage suppression - for the analog and digital
inputs and outputs, a zener diode network or a commercially
available surge suppressor may be connected in parallel with the
input circuit as shown in Figure 6-26 and Figure 6-27.
If a digital port experiences a severe surge its protective trip may operate
(O.Ld1 trip code 26). For continued operation after such an event, the
trip can be reset automatically by setting Pr
10.034
to 5.
From the Drive
To the motor
Back-plate
Enclosure
Isolator
Coupling bar
From the
Drive
To the
motor
(If required)
Summary of Contents for 09201760D
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