Third-harmonic (triplen) neutral conductor loading
A phenomenon where, with non-linear single-phase loads (LED drivers, computers, variable-frequency drives), the third harmonic and its multiples (triplens) in the three phases are in phase with each other rather than cancelling out, so they add up in the neutral conductor instead of disappearing. This can make the current in the N conductor higher than in any individual phase conductor, even though the neutral traditionally has the same (or a smaller) cross-section. NEN 1010-5-52 therefore requires an oversized or duplicated neutral conductor, or a derating factor on cable current-carrying capacity, where significant third-harmonic loading is present.
Bij een kantoorverdieping vol led-verlichting en pc's meet de installateur met een stroomtang een N-stroom die 40% hoger is dan de gemiddelde fasestroom, en past daarom een verzwaarde nulgeleider toe.
Aannemen dat de nulgeleider bij een gebalanceerde driefasenbelasting altijd stroomloos of laagbelast is — bij veel niet-lineaire eenfasige apparatuur geldt dit juist niet.
See also
- → §523.6 (IEC 60364-5-52 Annex E) The neutral conductor under third-harmonic loading — why "it's unloaded anyway" is wrong
- → §411 Automatic Power Off (AUV)
- → NEN-EN-IEC 61439-1/-2 (3e editie) Group rated current replaces the simultaneity factor — sizing the main cable and distribution board
- → §413.3 Electrical separation (§413.3) — an isolating transformer as a protective measure without earthing
- → §528 (IEC 60364-5-52) §528 — Proximity to non-electrical services: why a cable should not just run next to a gas pipe
- → §543 (IEC 60364-5-54) Sizing the protective conductor — the adiabatic formula versus the simplified table