Understanding the impact of 60601 3rd edition on power design

July 19, 2013 // By Jeff Schnabel, CUI

 

Designers of medical systems are faced with changes and challenges as safety-standards legislation is updated around the world. Over the past couple of years, governments in Europe and North America have decided to move to the 3rd edition of the IEC 60601-1 standard, which has important ramifications for the power supplies they incorporate.

Covering many aspects of medical-systems safety, the IEC 60601-1 standard was first published in 1977, to be replaced by the 2nd edition, which was developed in the late 1980s. In 2005, the IEC published its 3rd edition. The 2nd edition has, in a number of jurisdictions, been in force for many years, but several key regions globally have recently made the move to adopt the 3rd edition standards.

The European Union withdrew the 2nd edition standard at the start of June 2012, replacing it with the 3rd. Products already on sale as well as products new to the market now must conform to the regional version of the IEC standard, EN 60601-1:2006. If 3rd edition assessments are missing for products currently on sale government agencies in the European Union can order sales of the affected equipment to be stopped.

Canada originally planned to move to IEC 60601-1 3rd edition at the same time but delayed introduction to April of this year.

The most recent change has come with the US, which set the cessation date for UL 60601-1:2003 – based on the 2nd edition of IEC 60601-1 – at the end of June 2013. Like Canada, only new products have to meet the 3rd edition criteria.

Some of the requirements of IEC60601-1 2nd edition are in potential conflict with the 3rd. Thus, complying with the latest edition may put a product out of compliance with the 2nd, and so make a product unmarketable in regions that still adhere to the earlier version. Countries still mandating IEC 60601-1 2nd edition include Japan, Australia, New Zealand and China. As a result, many vendors are working to meet both versions in the same design, which requires additional cost and effort.

Figure 1: IEC 60601-1 3rd edition adoption

The first edition of the standard established several levels of protection to handle the different types of equipment used in medicine, as well as setting requirements for power supplies that were more stringent than those use in more generic standards such as IEC 60950-1. Equipment needing to be designed to IEC 60601-1 was classified as anything operated in an area where patients reside.

The first edition specified a number of requirements for power supplies, such as the adoption of dual-fused inputs with leakage currents of 300µA or less to earth, or 500µA in North America, and 100µA or less to the chassis, providing the effective limit for a fault condition. Other criteria included minimum creepage of 8mm and clearance of 4mm in order to prevent shorts developing between PCB tracks and air gaps, respectively.

Electrical safety parameters for different types of medical equipment are highlighted in the 2nd edition standard with the most basic form, Type B, covering non-patient systems and those with no

Earlier this year the US followed the EU and Canada in moving to the 3rd edition of the IEC 60601-1 medical device standard. This change presents several challenges and adds layers of complexity for medical device designers. Here we look at the changes and their effect on implementing power supplies in medical devices.
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CUI, power supply design, IEC60601-1 standard, medical