This technical article describes a neutral current overload problem caused by harmonic currents in a modern electrical installation. It further highlights how monitoring at a resort site helped identify the issue and why neutral conductors can become the most heavily loaded conductors in harmonic-rich systems.
How the issue was identified and addressed
Power quality monitoring was carried out at a resort site to measure phase currents, neutral currents, and voltages. The logged data showed a very high neutral current caused by harmonics. This allowed the issue to be quantified and corrective actions to be planned. Elliot Ajose, Regional Sales and Technical Manager for CA UK, reviewed the data and confirmed the harmonic-induced neutral load condition as he explains below.
Monitoring Data from a Resort Site
Phase currents, neutral current, and voltages were recorded using a Chauvin Arnoux power and energy logger installed at the main distribution board supplying guest rooms, lighting, HVAC, and common facilities.
The neutral current averaged nearly double the typical phase current and peaked at 410.3 A, higher than any individual phase maximum. This pattern, shown in Figure 1, is a classic sign of harmonic-induced neutral overload, common in modern setups where most equipment is non-linear and draws current in small, abrupt pulses.
The data shows that the neutral conductor was heavily loaded even when phase currents were moderate – indicating significant Triplen harmonics in the system.
Harmonic Multiplication Effect on the Neutral Conductor
The green fundamental currents at 50Hz are separated by 120 degrees and canceled in the neutral. The red harmonic alignment effect as seen in Figure 2., harmonic currents at 150Hz (3rd harmonic) align in phase and add in the neutral. The same effect occurs for the 9th,15th 21st and all other triplen harmonics.
This harmonic multiplication effect on the neutral can overload the neutral conductor. Many neutral conductors are the same size as phase conductors, which are no longer suitable in harmonic rich environments. In older installations, the neutral was sometimes reduced in size, which is dangerous in modern systems.
If the neutral overheats, insulation can fail, connections can burn, and the neutral can be lost. This can cause serious problems for the entire electrical system and connected equipment.
Voltage Monitoring Results
Site data showed stable phase to neutral voltages with averages of:
Although voltage was stable during monitoring, the high neutral current indicates a potential failure risk. Without monitoring, a neutral failure could go undetected until equipment damage occurs. Continuous monitoring is required to detect abnormal neutral current and voltage imbalance conditions.
Harmonic Observations
Analysis of consumption showed a strong third harmonic component on all three phases, with ninth and fifteenth harmonics also present but at lower levels. The third harmonic was clearly the dominant component, which explains why the neutral current was so high.
The captured waveforms were heavily distorted, with sharp current peaks. This is typical of LED drivers, switched-mode power supplies, and other electronic loads. Harmonic distortion was not constant and increased during the evening period, when lighting and guest room loads were at their highest.
Daily Load Profile and Neutral Behaviour
Load trends showed that phase currents followed expected daily patterns, with peaks during morning HVAC operation and evening guest activity. Neutral current followed a different pattern. Neutral current remained high even when phase currents were moderate, indicating that neutral loading was driven by harmonic content rather than fundamental load imbalance.
During low occupancy periods, neutral current remained elevated due to continuous electronic loads such as servers, networking equipment, security systems, and control systems. This behaviour is typical in modern commercial facilities where electronic loads operate continuously.
To be noted – the CA 6117 multifunction tester is a good alternative to run harmonic analysis. It was recently used at a large manufacturing plant, where the maintenance team noticed overheating of the neutral conductor in one of the main distribution boards.
Using the CA 6117 Multifunction Tester and clamp, they checked the three-phase supply for harmonics:
- Voltage and current harmonics up to the 50th order were measured.
- 56% of the load profile was identified on the 3rd harmonic adding in the neutral conductor.
- The 9th and 15th harmonics were found at a smaller magnitude but still present, causing significant neutral overload.
- Harmonics issues pinpointed towards the UPS system, and a passive harmonic filter was fitted.
Protection and monitoring limitations
Most protective devices are installed on phase conductors only. Neutral conductors often have no overcurrent protection. Residual current devices detect leakage but not neutral overload. Overcurrent relays typically do not measure neutral currents.
This means neutral overload can exist without triggering alarms or trips. Monitoring equipment is required to measure neutral current directly. Permanent monitoring systems or a Chauvin Arnoux PEL113 Power and Energy Logger can provide alarms when neutral current exceeds thresholds and helps prevent failures.
The progress made
Power and energy monitoring was carried out at the resort site to measure phase currents, neutral current and voltages. The monitoring identified very high neutral current caused by harmonics. The data confirmed that the neutral conductor was overloaded and at risk of overheating or even worse a lost neutral.
Want the full story on field insights, operational and safety compliance tips, and how customers can benefit from locating harmonic issues? View the complete case study on our website: cauk.net
This article appeared in the March 2026 issue of Energy Manager magazine. Subscribe here.