The changes follow the publication of the second edition of IEC 62368 in 2014, legislation that, in the power supply world, refers to safety regulation for both industrial and instrumentation (60950), and audio and video equipment.
Although IEC 62368-1 is a revision of the first edition published in 2010, it is one that brings with it major changes in approach to safety regulation. Most manufacturers will today use standards such as EN 60065 and EN 60950-1 for safety certification. The European Union expects to withdraw these standards on 20 June 2019 in favour of EN 62368-1, which is based on the original IEC version. The same date has been adopted by Underwriters’ Laboratories (UL) in the US for its own introduction of a safety regime based on IEC 62368-1.
Recognising the wide range of applications for digital devices, the shift to the second edition of IEC 62368-1 sees a change in the way in which safety engineering is performed. It is increasingly difficult to set rules that can cover the enormous spectrum of devices that now comprise IT and audio and video equipment. It is a range that spans portable music players through to computer servers and audio video projectors. The shift away from traditional safety standards mirrors similar changes in standards such as IEC 60601 for medical devices where prescriptive rules are removed in favour of approaches based on risk or hazard analysis.
Because of the radical change in approach, it is important that the design community understands the new regime. The core of IEC 62368-1 is its approach to hazard-based safety engineering (HBSE). Conceptually, it divides the analysis in three components: the hazardous energy source; the transfer mechanism; and the parts of the body likely to be affected. To ensure effective safety engineering, the key is to place a safeguard between the energy source and the body.
The energy sources are classified according to intensity. Class 1 covers energy sources that are safe to touch by ‘ordinary persons’ – the systems’ intended users. For electrical hazards, these have voltage and current limits and are roughly analogous to the SELV circuits described in IEC 60950.
However, energy sources need not only be electrical. The standard covers chemical and mechanical sources among others to be as comprehensive as possible. If it can be hazardous, it needs to be considered.
A Class 2 source is an energy source with levels exceeding Class 1 limits but with its own upper limit. Contact with the body may be painful but not likely to cause an injury. The energy in a Class 3 source, when it comes into contact with a body part, is one that is capable of causing injury. If the energy source is fire or one that can cause ignition, the Class 3 source is one that will lead to the spread of flames where fuel is available. Further criteria for Class 1 are that abnormal operating conditions do not lead to a single fault condition and that single-fault conditions do not lead to Class 2 limits being exceeded.
To work with HBSE, the