I agree a high THD between the neutral and the earth could indicate a high impedance in the neutral-ground connection. However, other factors could also contribute to the harmonic distortion in the power system. One of them is the nature of the loads connected to the distribution boards. Non-linear loads, such as electronic devices, motors, and lighting systems, draw current in a non-sinusoidal manner, creating harmonic currents that distort the voltage waveform. Another factor is the balance of the three-phase system. If the phases have different impedances or loads, the resulting current imbalance can also generate harmonic currents. These harmonic currents can cause a voltage drop in the neutral conductor, which is reflected in the THD measurement.

I agree a high THD between the neutral and the earth could indicate a high impedance in the neutral-ground connection. However, other factors could also contribute to the harmonic distortion in the power system. One of them is the nature of the loads connected to the distribution boards. Non-linear loads, such as electronic devices, motors, and lighting systems, draw current in a non-sinusoidal manner, creating harmonic currents that distort the voltage waveform. Another factor is the balance of the three-phase system. If the phases have different impedances or loads, the resulting current imbalance can also generate harmonic currents. These harmonic currents can cause a voltage drop in the neutral conductor, which is reflected in the THD measurement.