DIN VDE 0100-520 Beiblatt 3:2012-10

Requirements for the erection of cables are contained in DIN VDE 0100-520 (VDE 0100-520). They shall contribute to proper operation of electric installations and prevent, in consideration of suitable measures, that persons and livestock are placed in danger in the case of neutral conductors additionally stressed by harmonic currents or that a fire hazard results. Non-linear 1-phase consumers have harmonic content in the load current. For symmetrical distribution of these 1-phase loads to the 3 line conductors of an upstream three-phase AC system the 50 Hz currents in the neutral conductor extinguish themselves. This does not apply for the higher frequency currents that are caused by non-linear loads. An additional current load results in the neutral conductor of the distribution circuit due to these harmonic currents. This supplement contains information about the load of the neutral conductor due to harmonic currents and the effect on the current-carrying capacity of cables in three-phase distribution currents. Moreover it is explained which measures shall be selected if the harmonic proportion of the line conductor is so high that the current in the neutral conductor can exceed the continuous current-carrying capacity of this conductor. The responsible committee is UK 221.2 "Schutz gegen thermische Auswirkungen/Sachschutz" ("Protection against thermal effects/Property protection") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.