It is not a correct procedure to measure the voltage with respect to ground (earth) in drive, since it will measure the floating voltage in the circuit.
If we check correctly, during measurement we do not get any voltage between phase to phase measurement, hence the drive can be used without any problem. In all the VFD's the U,V,W output terminals are not fully insulated. Hence in Ready state even it do not deliver any power, an residual voltage still exist. The people must not touch them even if the product is Ready.

The voltage residual come from homopolar voltage when the neutral of transformer is connected to the earth, So it is normal to found 50Vac with 150Hz frequency. Regarding the DC voltage we may measure the value of 270Vdc(approx.)and it is normal floating voltage in all drives. We reconfirms that, it is a normal behavior of drive and you can continue using the drive without any problem due to this residual voltage.

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