GE AF-650 GP Design Manual page 153

7.8.2 Earthing
The following basic issues need to be considered when installing a frequency converter, so as to obtain electromagnetic compatibility (EMC).
• Safety earthing: Please note that the frequency converter has a high leakage current and must be earthed appropriately for safety reasons. Apply local
safety regulations.
• High-frequency earthing: Keep the earth wire connections as short as possible.
Connect the different earth systems at the lowest possible conductor impedance. The lowest possible conductor impedance is obtained by keeping the conductor
as short as possible and by using the greatest possible surface area.
The metal cabinets of the different devices are mounted on the cabinet rear plate using the lowest possible HF impedance. This avoids having different HF voltages
for the individual devices and avoids the risk of radio interference currents running in connection cables that may be used between the devices. The radio
interference will have been reduced.
In order to obtain a low HF impedance, use the fastening bolts of the devices as HF connection to the rear plate. It is necessary to remove insulating paint or
similar from the fastening points.
7.8.3 Safety Earth Connection
The frequency converter has a high leakage current and must be earthed appropriately for safety reasons acording to EN 50178.
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The earth leakage current from the frequency converter exceeds 3.5 mA. To ensure a good mechanical connection from the earth cable to
the earth connection (terminal 95), the cable cross-section must be at least 10 mm
7.9 EMC-correct Installation
7.9.1 Electrical Installation - EMC Precautions
The following is a guideline to good engineering practice when installing frequency converters. Follow these guidelines to comply with EN 61800-3 First environ-
ment. If the installation is in EN 61800-3 Second environment, i.e. industrial networks, or in an installation with its own transformer, deviation from these guidelines
is allowed but not recommended. See also paragraphs CE Labelling, General Aspects of EMC Emission and EMC Test Results.
Good engineering practice to ensure EMC-correct electrical installation:
• Use only braided screened/armoured motor cables and braided screened/armoured control cables. The screen should provide a minimum coverage
of 80%. The screen material must be metal, not limited to but typically copper, aluminium, steel or lead. There are no special requirements for the mains
cable.
• Installations using rigid metal conduits are not required to use screened cable, but the motor cable must be installed in conduit separate from the control
and mains cables. Full connection of the conduit from the drive to the motor is required. The EMC performance of flexible conduits varies a lot and
information from the manufacturer must be obtained.
• Connect the screen/armour/conduit to earth at both ends for motor cables as well as for control cables. In some cases, it is not possible to connect the
screen in both ends. If so, connect the screen at the frequency converter. See also Earthing of Braided Screened/Armoured Control Cables.
• Avoid terminating the screen/armour with twisted ends (pigtails). It increases the high frequency impedance of the screen, which reduces its effectiveness
at high frequencies. Use low impedance cable clamps or EMC cable glands instead.
• Avoid using unscreened/unarmoured motor or control cables inside cabinets housing the drive(s), whenever this can be avoided.
Leave the screen as close to the connectors as possible.
The illustration shows an example of an EMC-correct electrical installation of an IP 20 frequency converter. The frequency converter is fitted in an installation
cabinet with an output contactor and connected to a PLC, which is installed in a separate cabinet. Other ways of doing the installation may have just as good an
EMC performance, provided the above guide lines to engineering practice are followed.
If the installation is not carried out according to the guideline and if unscreened cables and control wires are used, some emission requirements are not complied
with, although the immunity requirements are fulfilled. See the paragraph EMC test results.
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or 2 rated earth wires terminated separately.