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HVAC Drive H300 103
Issue Number: 3
A complete 360
°
termination of the shield to the terminal housing of the
motor is beneficial.
From an EMC consideration it is irrelevant whether the motor cable
contains an internal (safety) ground core, or if there is a separate
external ground conductor, or where grounding is through the shield
alone. An internal ground core will carry a high noise current and
therefore it must be terminated as close as possible to the shield
termination.
Figure 4-40 Grounding the motor cable shield
Unshielded wiring to the optional braking resistor(s) may be used
provided the wiring runs internally to the enclosure.
If the control wiring is to leave the enclosure, it must be shielded and the
shield(s) clamped to the drive using the grounding bracket as shown in
Figure 4-41. Remove the outer insulating cover of the cable to ensure
the shield(s) make direct contact with the bracket, but keep the shield(s)
intact until as close as possible to the terminals
Alternatively, wiring may be passed through a ferrite ring, part number
3225-1004.
Figure 4-41 Grounding of signal cable shields using the
grounding bracket
4.11.7 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 0.3 m (12 in) away from the terminal block.
Figure 4-42 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 4-43 Connecting the motor cable to an isolator /
disconnect switch
Isolator
Coupling bar
From the
Drive
To the
motor
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