What is harmonic distortion in EV charging?
Harmonic distortion is a change in the shape of an electrical current or voltage waveform caused by harmonic components [S1]. Chargers and inverters can make it relevant to your connection application. ENA G5/5 uses a 3-stage assessment framework for individual and total harmonic voltage distortion [S2]. Ask which assessment your proposed equipment needs before ordering it. Checked October 2026.
What does harmonic distortion mean?
Harmonic distortion is a departure from the normal electrical waveform caused by harmonic components in current or voltage [S1]. Power electronics in charging and inverter equipment make waveform quality a connection-design issue [S3].
Why it matters for your site: distorted current can contribute to overheating, losses and malfunctioning controls [S1]. A charger power rating alone does not establish that the proposed installation is acceptable.
What does ENA G5/5 limit at the connection point?
G5/5 is Engineering Recommendation G5 Issue 5. It sets planning and compatibility levels for individual and total harmonic voltage distortion, with a three-stage connection assessment process [S2]. In plain English, your proposed equipment must fit within the network’s available allowance for distortion; there is no single catalogue percentage that proves every site acceptable.
Ask your distribution network operator (DNO), the company running your local network, to identify the assessment point, applicable limits and equipment data required. Use the DNO application guide for the wider connection process.
When might the DNO request an assessment?
Network research identifies high-capacity chargers among loads that may require harmonic assessment before connection [S3]. ENA’s equipment guidance specifically discusses G5/5 assessment for equipment above 75 amperes per phase [S1]. This is not a universal exemption for smaller installations.
Request the manufacturer’s harmonic test data and a report covering the combined proposal. Ask which existing loads, chargers and inverters were included, which operating conditions were tested and whether mitigation is needed. Keep power factor separate from harmonic assessment: a satisfactory value for one does not document the other.
Next step
Collect the connection offer and equipment schedule for the site-power tool. Use the charging cost tool for separate energy-cost calculations, then get matched with an installer that covers your area.
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Common questions
Is this the same as using too much power?
No. Harmonics concern waveform distortion and power quality. ENA identifies overheating and control maloperation among potential effects, rather than treating them simply as excessive demand [S1].
Does every charger need a detailed network study?
No. ENA describes product-standard routes and staged assessments. Give the network the equipment data and ask it to confirm the applicable route [S1].
What does THD stand for?
Total harmonic distortion. G5/5 addresses total and individual harmonic voltage distortion; ask whether a reported result describes voltage or current before comparing it with a limit [S2].
Can a low current-distortion figure prove site compliance?
It is only part of the evidence. G5/5 assesses connections using individual and total voltage-distortion planning and compatibility levels; request the assessment for the proposed arrangement [S2].
Which operating condition should the equipment data cover?
Request the most onerous condition. ENA's equipment guide seeks harmonic emissions across operating power levels, rather than relying solely on a full-output result [S1].
Ask about your site
Sources
- Heat pump and EV chargepoint database guide, Energy Networks Association,Last checked 19 October 2026
- Engineering Recommendation G5 Issue 5 scope, Energy Networks Association,Last checked 19 October 2026
- LCT harmonic limits project, Energy Networks Association,Last checked 19 October 2026