NVF5 Series User Manual Chapter 3 Installation and Wiring
grounding to realize 360-degree circular connection. It is prohibited to twist the shielding
layer before connecting it to the inverter in case that the shielding effect is lowered greatly
or even lost.
A shielding cable or an independent cable tray shall be adopted between the inverter
and the motor. One end of the shielding layer of the motor cable or the metal shell of the
cable tray is connected nearby the inverter, and the other end is connected with motor
shell.
The grounding cable shall be as short and thick as possible so as to lower grounding
impedance, grounding cables shall be far away from the input side and the output side of
noise-sensitive devices.
3.7.3 Leakage Current Suppression
Leakage currents include line leakage currents and grounding leakage currents. The
magnitude of a leakage current depends on distributed capacitance of the system in the
wiring process and the carrier frequency of the inverter. The leakage current can be
effectively lowered by reducing the carrier frequency and using motor cables as short as
possible. When the motor cable is long (50m or above), an AC output reactor or a sine
wave filter shall be installed at the output side of the inverter; when the motor cable is
longer, it is supposed to install one reactor at a certain distance.
Two classification and expression modes of leakage currents are：
Grounding leakage current: means the leakage current flowing through a common
grounding cable. It may flow into the inverter as well as other devices through the
grounding cable. The leakage current may cause malfunction to a residual-current circuit
breaker, a relay or other devices.
Lines leakage current: means the leakage current flowing through distributed
capacitors among the cables at the input side and the output side of the inverter. The
magnitude of the leakage current is relevant to the carrier frequency of the inverter, the
length of the motor cable and the sectional area of the cable. The higher the carrier
frequency of the inverter, the longer the motor cable and the larger the sectional area of
the cable, the larger the leakage current is.
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