When preparing projects and implementing electrical installations, it is crucial to select conductors with the appropriate cross-section and length. When preparing non-linear circuits, one of the most important elements of the installation is the natural conductor, which, for example, in three-phase circuits should have zero electric charge. Do you want to know what the cross-section of the neutral conductor should be for installations with a non-linear circuit? Learn more and carry out installation work in accordance with applicable standards.
Check the installation cables at the Onninen wholesaler
The influence of the third harmonic current on the actual current-carrying capacity of the conductor
The presence of the third harmonic current in electrical circuits significantly affects the actual load capacity of conductors, especially the neutral conductor. The third harmonic, which is one of the most common harmonics, does not disappear in the neutral conductor, but is added to the harmonics coming from other phases.
In a three-phase power system, this can lead to excessive current in the neutral wire, which results in overload and overheating. As a result, it may be necessary to increase the cross-section of the neutral wire to avoid the dangerous effects of overheating.
What cross-section of a natural conductor in non-linear circuits will be optimal?
The PN-HD 60364-5-52 standards indicate that the cross-section of the neutral (N) conductor should be equal to or greater than the phase conductor . In this case, the level of harmonic distortion of the current and the actual load capacity of the conductors are of key importance.
In practice, we distinguish between two situations in which cables and electrical wires of different cross-sections are used:
- The cross-section of the natural conductor is equal to the cross-section of the phase conductor – this method of selecting conductors is used in circuits where the third-order harmonic level is on average up to 33%. Then the diameter of the N conductor should be at least the same as the phase conductor, e.g. 16 mm2 for copper and 25 mm2 for aluminum.
- The cross-section of the natural conductor is larger than the cross-section of the phase conductor – such installation conductors are used when third-order harmonic circuits exceed the level of 33% of the distortion factor. By using a thicker N conductor, we avoid overloads in the network.
As an installer, you need to know which power cables will be the optimal solution in electrical installations. With a natural conductor with higher harmonic deviations, a larger cross-section is necessary.
The Difference Between the Third Harmonic in Neon Lighting and Electronic Power Supply
The cross-section of the neutral wire is incredibly important, especially when it comes to non-linear receivers. When it comes to the cross-sections of wires in neon lighting and electronic power supplies, we can talk about the following differences:
- Neon Lighting – Here the third harmonic is created by nonlinear current flow through the cables in the lamp. The nonlinearity causes the third harmonic to generate interference in the system and reduce the efficiency of current flow in the circuit.
- In electronic power supplies – a good example are SMPS power supplies, where the third harmonic is the result of the current conversion process. The device draws current non-sinusoidally, which increases the currents in natural conductors. This means that, according to the applicable standards, a larger cross-section should be found in N conductors.
Therefore, harmonics are currents or voltages with frequencies that are integer multiples of the fundamental power frequency.