Voltage distortion at your service, caused by nonlinear loads down the line (even from neighbors), can absolutely be caused by both line-to-line and line-to-neutral loads. Your initial thought is likely incorrect. Here's why: Harmonic Currents

Nonlinear loads (like variable frequency drives, electronic ballasts, computers, etc.) draw current in a non-sinusoidal fashion. This creates harmonic currents – currents at frequencies that are multiples of the fundamental frequency (60 Hz in North America).

Impedance and Voltage Drop

When these harmonic currents flow through the impedance of the utility's distribution network (transformers, conductors, etc.), they create voltage drops at those harmonic frequencies. This voltage drop, when added to the fundamental voltage, results in voltage distortion.

Line-to-Neutral vs. Line-to-Line and the Neutral Conductor



Line-to-Neutral Loads

These are very common in residential and commercial settings. Especially single-phase loads that connect between a phase and neutral. The key here is that

single-phase, nonlinear loads (connected line-to-neutral) produce significant third-harmonic currents. Third harmonic currents are particularly problematic because they are additive in the neutral conductor in a three-phase, four-wire system. Since the neutral wire has impedance, this elevated third-harmonic current causes voltage distortion on all three phases because they all share that neutral. Line-to-Line Loads

These nonlinear loads can produce a wider range of harmonic currents. These harmonics affect the line-to-line voltages directly.

Three-Phase, Four-Wire System

The common configuration for many distribution systems is a three-phase, four-wire system (three phases and a neutral). In this system, line-to-neutral loads are connected to one of the phases and the neutral. This allows for both 120V (phase-to-neutral) and 208V (line-to-line) or 240V(line-to-line) circuits.

Why are third harmonics so important? Neutral Overload

In a balanced three-phase system with only linear loads, the neutral current is ideally zero. However, with third harmonics, the currents don't cancel out; they add together in the neutral. This can lead to: Overheating of the neutral conductor Elevated neutral-to-ground voltages (sometimes called "neutral shift") Increased voltage distortion across the system.

Transformer Problems

Third harmonic currents in the primary winding of a delta-wye transformer get trapped in the delta winding, causing core saturation, heating, and potential transformer damage.

In summary

Both line-to-line and, especially, line-to-neutral nonlinear loads can contribute to voltage distortion on your service. The additive nature* of third harmonic currents in the neutral of a three-phase, four-wire system makes line-to-neutral single-phase nonlinear loads a major source of voltage distortion. Don't underestimate their impact, especially in buildings with a high density of electronic equipment.

To diagnose the source of voltage distortion, consider these steps


Voltage and Current Harmonic Analysis

Use a power quality analyzer to measure the voltage and current waveforms at your service and at suspect loads. This will show the amplitude and frequency of the harmonics present.2.

Load Monitoring

Monitor the current draw of various loads to identify the major contributors to harmonic distortion.3.

Consider Harmonic Mitigation: If the voltage distortion is excessive, consider installing harmonic filters or using harmonic-mitigating equipment. Flag for review