80 Unidrive M/HS Frame 5 to 6 Power Installation Guide
Issue Number: 9
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 4-25 and Figure 4-26.
If a digital port experiences a severe surge its protective trip may operate (I/O Overload trip). For
continued operation after such an event, the trip can be reset automatically by setting Pr 10.034 to 5.
Figure 4-25 Surge suppression for digital and unipolar inputs and outputs
Figure 4-26 Surge suppression for analog and bipolar inputs and outputs
Signal from plant Signal to drive
0V 0V
30V zener diode
e.g. 2xBZW50-15
Signal from plant Signal to drive
0V 0V
2 x 15V zener diode
e.g. 2xBZW50-15
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