Conforming with Worldwide Safety and EMC/EMI Standards

Nov 1, 2010 12:00 PM
Don Tuite Analog & Power Editor, Electronic Design

Find a downloadable version of this story in pdf format at the end of the story.

Many designers think meeting the worldwide safety standards for power supplies in mains-powered products involves following a simple checklist to ensure their designs don't run into distribution problems in some countries due to a lack of dotted i's or crossed t's. But that's a naÏve perspective. The truth is that most designers need some serious hand-holding during their first several designs. This task can't be addressed with a checklist and a positive attitude.

Also, safety is critical, since you don't want to electrocute your end user. Yet basic safety is the least of your worries. In fact, it isn't too difficult to demonstrate conformity if you use already-approved components, except in the case of medical products.

The catch is that the safety requirements are in the same standards as electromagnetic-compatibility (EMC) and electromagnetic-interference (EMI) requirements. You won't know if your product has any problems in those areas until you run the tests at the testing labs, and then you have to solve the problems ad-hoc in real time.

That's why you should ask experts questions about your specific situation and follow their recommendations. Your best bet is simply to find an OSHA-certified (Occupational Safety and Health Administration) nationally recognized testing laboratory (NRTL) or the equivalent overseas. One NRTL is Underwriters Laboratories (UL) itself. However, a number of others can be found on the UL Website, any of which can test for UL certification. There's a parallel path for overseas approval. Allowing for deviations that are familiar to the experts, the fundamental requirements remain the same.

The markings for your product will differ in each country. Core standards for power supply safety and electromagnetic compatibility and interference are the European IEC 60601 (Measurement, Control, and Lab Equipment) and 60950 (Information Technology Equipment) standards, including their various dash-numbered subparts. In the U.S., they get “UL” prefixes. In Europe, they get “EN” (for “European Norm”) prefixes.

EMC AND EMI PROTECTION

There's more to these marks than electrical safety. Industry guru Derek Krous, who has gone through a number of certifications, said obtaining UL's approval for the electrical safety of a new product using an approved power supply is usually much easier than meeting the specs for EMC and EMI.

For a detailed description of the challenges involved, check out “EMC Testing/ Immunity Testing for the CE Mark,” an article by Rodger Gensel, in the March 15, 2007, issue of Conformity at www.conformity.com/artman/publish/printer_166.shtml. Gensel's article focuses on European EMI requirements. But as in the case of electrical safety, there's more overlap than difference these days.

Essentially, Gensel said the European Union requires manufacturers of electronic equipment to meet the EMC guidelines of EC Council Directive 89/336/EEC. Thetest requirements are issued by CENELEC, the European Committee for Electro-technical Standardization.

Generic immunity standards are called out in EN 61000-6-1 and EN 61000-6-2, and generic emission requirements in EN61000-6-3 and EN 61000-6-4, and sometimes there may be specific test requirements as well. The International Electrotechnical Commission (IEC) creates “Basic Standards” that define the specific tests, test methods, setups, and test equipment.

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