For CE, UKCA, or UKNI marking, we now probably need to apply Magnetic Field tests (Merely applying the 'relevant harmonised standards' is no longer sufficient)

23 Jun 2025

Keith Armstrong, www.cherryclough.com, 11 April 2025

Traditionally, magnetic fields were only considered to be caused by mains power currents, which is why most generic, or product EMC standards require applying the IEC 61000-4-8 immunity test at 50Hz. Also, a traditional niche has long existed in professional audio applications, which are exposed to strong magnetic fields over 50Hz - 10kHz, hence the reason for the magnetic field tests in EN 55103-1 (emissions) and EN55103-2 (immunity, being replaced by EN 55035 in July 2022).

But nowadays, we are increasingly driving powerful motors from variable frequency drives (VFDs), and using Electronic Article Surveillance (EAS) in retail shops. Also, we are increasingly using Wireless Power Transfer (WPT) and Radio Frequency Identification (RFID) just about everywhere. These all create powerful magnetic fields in the range 1kHz to 26MHz, causing new risks to the correct operation of our products and equipment.

The military have long tested magnetic field immunity using MIL STD 461’s RS101, or DEF STAN 59-411’s DRS01 – but they only went up to 100kHz. But now we can test magnetic field immunity up to 26MHz by using IEC 61000-4-39.

But why am I writing about this? After all, very few generic or product-family test methods ‘harmonised’ under the EMC Directive in the Official Journal of the EU (OJEU) call up IEC 61000-4-39 testing. (But note that the latest version of the Medical EMC standard, IEC 60601-1-2, does require such magnetic field immunity tests.)

We should be concerned, because the traditional approach of declaring EMC compliance by choosing the most relevant generic or product-family EMC standards listed in the OJEU – then passing the tests they specify, and listing them on your Declarations of EMC Conformity – is 5 years out of date!  Products might suffer costly delays in EU and UK customs as a direct result.

Since the EMC  Directive 2014/30/EU (and the UK’s EMC Reg’s) came into force in 2016, we have been required to perform, and document, an “adequate analysis and assessment of the risks” of our products’ complying with the Directive’s Essential Requirements.

The purpose of these “EMC risk assessments” is to specify the EMC standards, specifications, guidelines, etc., – or parts of them – to apply to our products to help ensure their EMC compliance in real life.

Magnetic field tests such as IEC 61000-4-39 are an increasingly necessary requirement in these risk assessments.

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