Chapter 1 Introduction | VFD-ED
Isolating main power from ground
When the power distribution system for the motor drive is a floating ground system (IT Systems) or an
asymmetric ground system (Corner Grounded TN Systems), you must remove the RFI switch. Removing
the switch also cuts off the internal RFI capacitor (filter capacitor) between the system's frame and the
central circuits to avoid damaging the central circuits and reduces the ground leakage current.
Important points regarding ground connection
To ensure the safety of personnel, ensure proper operation, and reduce electromagnetic radiation,
you must properly ground the motor and drive during installation.
The diameter of the grounding cables must meet the size specified by safety regulations.
You must connect the shielded cable to the motor drive’s ground to meet safety regulations.
Only use the shielded cable as the ground for equipment when the above points are met.
When installing multiple sets of motor drives, do not connect the motor drives’ grounds in series. See
the following image.
Pay particular attention to the following points
Do not remove the RFI switch while the power is ON.
Make sure the main power is OFF before removing the RFI switch.
Removing the RFI switch also cuts the capacitor conductivity. Gap discharge may occur once the
transient voltage exceeds 1000 V.
NOTE: If you remove the RFI switch, you remove the reliable electrical isolation. In other words, all
controlled inputs and outputs become low-voltage terminals with basic electrical isolation. Also, when
you remove the internal RFI switch, the motor drive is no longer electromagnetic compatible (EMC).
Do not remove the RFI switch if the main power is a grounded power system.
You must remove the RFI switch when conducting high voltage tests. When conducting a high
voltage test for the entire facility, disconnect the main power and the motor if the leakage current is
too high.
Floating Ground System (IT Systems)
A floating ground system is also called an IT system, ungrounded system, or high impedance/resistance
(greater than 30 Ω) grounding system.
Disconnect the ground cable from the internal EMC filter.
In situations where EMC is required, check for excess electromagnetic radiation affecting nearby low-
voltage circuits. In some situations, the adapter and cable naturally provide enough suppression. If in
doubt, install an extra electrostatic shielded cable on the power supply side between the main circuit
and the control terminals to increase shielding.
Do not install an external RFI/EMC filter. The external EMC filter passes through a filter capacitor and
connects power input to the ground. This is very dangerous and damages the motor drive.
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