electrical installation harmonic problems part 2

Examples of harmonics-related malfunctions in electrical installations : case of  “Overloads in neutral conductors”

I come back here with an other case of malfunctions due to Harmonics

This article will present briefly the case of overloads in neutral conductors by third-order harmonics created by single-phase loads, leading to tripping, overheating and even cable damage

The third-order harmonic currents created by non-linear single-phase loads (IT, lighting) connected between phases and neutral accumulate in the neutral conductor.
In extreme cases, the current in the neutral conductor may be greater than the current in the phases.
This results in overloads and even damage of the neutral conductor, in particular if the neutral cross-section is half of that of the phase conductors.

A well-known example concerns the headquarters of Groupama in Paris.
In January 1992, a new computer system was installed.
Soon after commissioning, the main circuit breaker tripped, interrupting the operation of the entire system.
Following lengthy and costly investigations, it was established that the interruption was due to an overload in the neutral of the three-phase system, despite the fact that the system was perfectly balanced.
Strangely enough, the current in the neutral conductor was equal to 65% of the current in the phase conductors, whereas the protection relays had been set to 50%.

As the story goes, following the incident, all Groupama staff knew what harmonics were…

see you in 10 days with an other case
Jacques Schonek



  • This is an infarmatic for the professionals as a pocket dairy. and thanks for this info

  • is it bcoz of fault current or voltage swing due to new load instalation ??wy it had happen in single phase..i think 1ph is less dangerous than 3ph sys..
    harmonics r sine wave or cosine wave?

  • Hello their How u doing? I have really enjoyed your work.keep it up!! Pls send me electrical installation e books via my email address .Many thanks for your early reply .

  • please when you publish any case please put some single diagram or any dwg shown the as built system ,

  • hello please measure odd and even harmonics in c.c.p and to decided which harmoic rellay is caused like this phenomina. thanks

    • Basic & fundamental information. It is useful to all professional particularly for the Design & Planning Engineers of Electrical decilpine. Thanks a lot for Face book.

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