Harmonics and flicker: how to verify compliance?

If your product draws current from the public mains network, it almost certainly needs to meet the harmonic and flicker requirements of the BS EN 61000 series before it can be declared compliant with the EU EMC Directive or the UK EMC Regulations, and carry a CE or UKCA mark.

These aren't optional extras — they're mandatory provisions intended to protect the reliability of the public electricity supply and products connected to it.

What are harmonics?

The waveform of the current drawn by most modern electrical and electronic equipment (e.g. switch-mode power supplies, LED drivers, and motor controllers) is not sinusoidal. Accordingly, in addition to the fundamental 50 Hz component, the current includes harmonic components at frequencies multiple of 50 Hz. Harmonics cause overheating of the mains network (transformers, cables) and can affect the reliability of other devices and equipment connected to it.

BS EN 61000-3-2 sets the limits for equipment drawing up to 16 A per phase. Equipment is classified into four categories (A, B, C, D), each with specific maximum harmonic current values up to the 40th harmonic.

A separate standard, BS EN 61000-3-12, covers equipment from 16 A to 75 A per phase.

What is flicker?

Any equipment that causes repetitive changes in current draw (e.g. compressors cycling, large motors starting and stopping, welding equipment) can produce fluctuations on the mains supply voltage that can make the light emitted by lighting equipment visibly flicker. It's more than an annoyance because prolonged flicker can cause headaches, fatigue and reduces workplace productivity.

BS EN 61000-3-3 limits the amplitude and rate of the voltage fluctuations based on the estimate of the mains network impedance. A combined measure of amplitude and repetition rate is provided by the short-term flicker (Pst) which must be ≤ 1. For equipment with long operation time the long-term flicker (Plt) is calculated and must be ≤ 0.65. The amplitude of individual voltage fluctuations is also checked and % limits applied.

Similarly, BS EN 61000-3-11 extends the requirements to equipment up to 75 A per phase. Due to the large current intake, equipment in the scope of this standard might need a supply line with a suitably low impedance. Therefore, if the equipment complies with a max impedance value, its connection is subjected to a verification that the actual supply line is not higher than this max value.

Why does this really matter to you?

The ability to verify compliance with harmonics and flicker standards at an early design stage can be crucial to meet project deadlines. It is known that failing tests at the certification stage means costly redesign, re-testing, and delays to market, but this is particularly the case for corrective actions to resolve issues with harmonics or flicker, which generally involve a revision of fundamental design concepts, like control methods and principles of operation.

Catching issues early, during development, saves time and money.

The PPS ECTS2 system

The Pacific Power Source ECTS2 (Electromagnetic Compliance Test System) is a complete, turnkey harmonics and flicker test solution — available from Caltest.

Power Range: 750 VA – 100 kVA

EUT Current: Up to 75 A/phase

Phases: Single or three-phase

Included in every system: precision programmable AC power source, high accuracy measurement module, lumped flicker reference impedance, input/output panels and PPS Harmonics & Flicker (HFA) test software — pre-configured for the standards you need.

The ECTS2 covers BS EN 61000-3-2, BS EN 61000-3-3, BS EN 61000-3-11 and BS EN 61000-3-12 and it is assembled to expand the test capability to cover mains line immunity tests of the IEC 61000-4 series (e.g. BS EN 61000-4-11 – dips and interruptions, BS EN 61000-4-13 – interharmonics).

One system, complete compliance coverage.

If you have any questions about the harmonics and flicker or the PPS ECTS2 system, please don't hesitate to contact us. We're here to help you with any questions you might have.