A new approach to electrical safety testing

| Environmental Testing

Electric strength test on a television
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Jonathan Newell explains why now is the time to prepare for compliance to the IEC 62368-1:2014 hazard based safety standard for audio/visual (A/V) and information technology equipment (ITE).

Having received its first release as far back as 2010, the electrical safety standard from the International Electrotechnical Commission (IEC) had its most recent update in 2014. This version has been accepted as the mandatory standard to meet in order to receive CE marking in the EU after a five-year adoption period. In parallel, the US version (UL 62368-1) is the national version defining the standards required to gain certification for electrical equipment for IT, office and telecoms equipment.

Replacing existing standards

The five year adoption period ends in 2019, defined as the Date of Withdrawal (DoW) of the old standards which EN 62368-1 will replace. These are IEC 60950-1 for Information and Communications Technology and 60065 for A/V equipment.

The replacement of these well-established standards might imply some form of convergence where the two old documents are merged into one new one that encompasses all the relevant technologies. But this is far from the case. Companies which supply products which currently meet either of these old standards are well-advised to start making the transition to conform to the new version.

Changing landscape

There are fundamental differences between the old and the new standards – these represent a complete change in thinking in the approach to specifying the safety of electrical equipment.

IEC 60950-1 and IEC 60065 are “prescriptive” standards which set out how the objectives are to be achieved; whereas the new standard is “hazard-based” using a more flexible model for protecting users, operators and trained maintenance personnel from hazardous energy sources.

To illustrate how these approaches differ, a glance at the IEC 60950-1 standard will reveal the way in which certain values are prescribed in the form of a specification, such as the minimum size of protective bonding conductors based on the protective current rating of the circuit. This is a typical approach taken by prescriptive standards.

The hazard-based standard classifies electrical energy sources and their hazard levels relating to the people likely to be exposed to them, whether they are ordinary people (consumers), skilled people (eg service engineers) and instructed people (those working under the supervision of skilled people).

Electrical Energy Source Class 1 (ES1) describes the exposure limit that an ordinary person will encounter, ES2 sets the limit for instructed people and ES3 represents energy sources above the ES2 limit and which may be encountered by skilled people.

Different safeguards are required against exposure to different energy sources depending on the user. Generally, this means that for an ordinary person, no safeguards are required for ES1, one safeguard is needed for ES2 and there should be at least two safeguards in place to prevent the exposure of an ordinary person to class 3 electrical energy sources (ES3).

The thresholds between ES1, ES2 and ES3 depends on the nature of the energy source. For example, a charged capacitor of 170nF capacitance has an ES1 threshold of 75V and an ES2 threshold of 150V. For AC energy sources with a frequency over 100kHz, the ES2 limits are 140V RMS and 100mA RMS.

Electronic assembly courtesy of NXP

Flexibility

According to the international certification and testing organisation Underwriters’ Laboratory (UL), the use of a hazards-based standard instead of a prescriptive one offers greater flexibility to manufacturers of electronic equipment.

This flexibility stems from the ability to introduce new design concepts and construction techniques for the equipment with having to first require any corresponding amendments to the relevant standards in order to accommodate them. The manufacturer needs to demonstrate compliance to the new standard which has more flexibility to accommodate changes than the standards it replaces.

Misconceptions

According to the IEC, some confusion still persists regarding the nature of the standard and, despite the fact that hazard based safety engineering was used as the means of drawing it up, it is not based on risk analysis concepts and therefore risk-based considerations are not within the scope of the standard. The IEC makes it clear that although some risk analysis was performed in the development of the standard itself, there is no risk analysis involved in the application of the standard to individual products.

Similarly, this is not a generic hazard-based safety engineering standard and is very specific to the closely related technologies of IT and A/V systems, which must meet compliance criteria in detail. Although the new standard is based on a new approach, it is nonetheless very clear in its requirements to ensure consumer products meet very exacting safety criteria.

The standard achieves this by:

* Identifying and classifying energy sources
* Identifying the safeguards required for protection of different classes of personnel against these energy sources
* Qualifying the safeguards based on compliance criteria

Making the transition

With the DoW of the old standards expected to be the middle of 2019, just under four years remain for manufacturers to become compliant in Europe, Canada and the USA which allows some time but in some cases less than it would seem. As International compliance and testing company TÜV SÜD explains, one of the legacy standards is nearing the DoW for its current version as early as 2016. Companies developing products for release beyond July 2016 that fall within the scope of EN 60950-1, need to make a choice between adopting the new standard or adapting to meet the latest version of what will soon become a legacy standard.

There is also some leeway with the provision that components which were previously certified under the legacy standards will remain compliant when used in higher assemblies seeking certification under the new standard. This will significantly reduce the compliance burden on manufacturers of higher level assemblies.

Before 2019, manufacturers should consider two additional factors when deciding whether to adopt the hazard-based standard:

1 The need for dual certification before the DoW of the old standards, particularly in markets which haven’t yet signed up to IEC 62368-1

2 There could be advantages in starting the learning curve of compliance early to make the transition to the new standard smoother.

This latter point should be considered carefully, as TÜV SÜD believes that the new approach adopted by the hazard-based standard relies on expertise to identify potential hazards followed by the application of tests as set out in the standard to prove the effectiveness of safeguards designed to protect against those hazards.

“IEC 62368-1 introduces a completely new methodology, turning on its head the well-established and prescriptive approach of product safety compliance. A different mind-set is now required when applying the standard,” said TÜV SÜD Product Service’s Senior Manager, Richard Poate, emphasising the need to start now on the preparations for IEC 62368-1.  “While the two old standards closely dictate product designs, the new approach is to define hazard-based requirements, using engineering principles and taking into account relevant IEC equipment standards and pilot documents. To a large extent this makes IEC 62368-1 a technology independent safety standard, which allows for more design freedom.”

Jonathan Newell

Jonathan Newell

Jonathan Newell is a graduate of Loughborough University and has three decades of experience in engineering as well as broadcast and technical journalism.
Jonathan Newell

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