High Frequency Shielding - KEB COMBIVERT F5 Instruction Manual

1.4.10 High Frequency Shielding

Use of shielded cable is recommended when high frequency emissions or easily
disturbed signals are present. Examples are as follows:
- motor wires connected to inverters: connect shield to ground at both the
inverter and motor, NOTE the shield should never be used as the protective
ground conductor required by NEC. Always use a separate conductor for this.
- digital control wires: connect shield to ground at both ends.
- analog control wires: connect shield to ground only at the inverter.
The connection of meshed shields to the ground connection should not be done
through a single strand of the shield, but with metallic clamps to provide 360° contact
around the surface of the shield to the ground point. Connection with a single wire
bundle from the braided shield reduces the effectiveness of the shield 70%. Metal
conduit clamps work well for this. Be sure the fit is tight.
Ridged metal conduit can be used as the shield of the motor wires. Always observe
the following points :
- remove all paint from the control cabinet and motor housing where the conduit
is fastened
- securely fasten all conduit fittings
- run only the motor wires through the conduit, all other wires, high voltage AC
and low voltage signal, should be pulled through a separate conduit.
- connect the control panel to the Sub-panel with a heavy ground strap.
If EMI filters are used, they should be mounted to the inverter or as close as possible
to the inverter and on the same sub-panel as the inverter. Good metallic surface
contact to the sub-panel is required to provide adequate high frequency grounding of
the filter. Always use the shielding plate provided with the filter when connecting the
filter to the inverter.
Shielding of control wires:
If digital signal wires are terminated on a terminal block in the control panel, the
shields should be firmly connected to the sub-panel on both sides of the terminal
block.
The shields of digital signal wires originating outside the control cabinet which are
not terminated on a terminal block, must be connected to the sub-panel at the point
where the cable enters the control panel and at the inverter.
If the shield is terminated to the sub-panel within 8 inches (20cm) of the inverter,
then the shield no longer needs to be connected to the inverter.
When using un-shielded signal wires, they should always be installed as a twisted
pair (signal and common).
Low voltage signal wires should cross high voltage wires at right angles.
General
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