A classic example is related to the neutral conductor in three-phase systems. In a system with little distortion, little unbalance and a balanced (or slightly unbalanced) receiver, the current in the neutral conductor has the tendency to be much smaller that RMS phase currents. This has resulted in the temptation of some designers to obtain savings by installing neutral cabling with a smaller cross section than in phase conductors. Everything can go well until the appearance of odd harmonic orders which are multiples of 3 (third, ninth, etc.). These harmonic currents flowing in the neutral conductor might not zero in the neutral conductor and they may sum up. These high harmonic currents and skin effect contribute to the neutral conductor heating.