How does the 4th pole switching reduce harmonic voltages ?
Conductors like copper cables are not perfect conductors of electricity and they have some loss when carrying the currents. They have a DC resistance or volt drop. Similarly for AC currents there is an additional Impedance drop (inductive) caused by the fields produced by the currents flowing. If the cables are well grouped (e.g. R, W, B & N in a tight trefoil configuration) then this inductive impedance is reduced because the fields cancel reducing the effective inductance. Once separated the field no longer effectively cancel. Impedance drops are inevitably several orders larger than the resistive drops and contribute to the end voltage at the point of usage especially if the cable runs are long. The larger the current harmonics caused by the load the greater the voltage distortion caused by the series impedance introduced by the separation of currents. Hence by switching the neutral as w3ell as the active conductors (e.g. 4-pole), it is possible to steer the currents back to their s
