Safety Design and Certification for Test and Measurement Products Part 1

Have you ever designed a product that you thought was ready to ship only to have it fail testing by not meeting safety requirements? Months can be lost and mistakes repeated if a company doesn’t have a first-class safety design philosophy and certification process in place.

Before embarking down the safety design and certification path, an understanding of the important role standards and certification play is essential. When designers become familiar with safety design issues and institute a safety certification process, delays in the shipment of products can be avoided.

Safety certification marks are commonplace in the United States and Europe for household appliances (HHA) and information technology (IT) equipment (computers) due to long-time consumer awareness of potential hazards from electronic products. Safety marks include UL and CSA for North America and VDE, TUV, and Demko for Europe.

Safety awareness among test and measurement product users is increasing because of new high-voltage measurement categories and extra precautions required for safe operation. For example, test and measurement products may see voltages of 1,000 V or higher, which can be accessible during measurement operations via test probes.

In addition to high-voltage potentials, test and measurement products are used in commercial establishments, laboratories, industrial areas, or hazardous locations that require extended operating conditions such as higher temperatures, pollution, or potentially explosive atmospheres. Test and measurement products generally need special installation procedures, labeling requirements, and operating instructions.

Compliance Standards

Standards are the cornerstone of compliance and the technical rules for product safety design and testing. Areas covered by safety standards include components, enclosures, grounding, insulation, classification, temperature limits, labels and markings, documentation, flammability, and testing.

International technical committees (TC) such as TC66 for test and measurement products develop International Electrotechnical Commission (IEC) standards with inputs from industry, test bodies, and other interested parties. IEC standards are the basis for most standards including UL/CSA and European Norms (ENs).

Standards are considered the minimum acceptable criteria. When a product conforms to the relevant standards, a presumption of conformity exists for the CE Marking. There is no presumption of conformity when standards are not used.

The IEC 61010-1 standard for test and measurement equipment specifies safety requirements for electrical products and associated accessories intended for professional, industrial-process, and educational use when used for test and measurement, control, and in laboratories.

Certification Bodies and Marks

Many countries require proof of safety conformity for electrical products either by a manufacturer’s self-verification or a third-party certification mark. Some laws make safety conformity a legal requirement. And with U.S. building codes (NEC), state safety laws, and so many product liability suits, safety conformity is a must for manufacturers in North America.

Certification is an attestation from an accredited third-party verifying that a product or component complies with the relevant standards. Certification allows marks to be affixed to products as visual evidence of conformity. European testing laboratories and certification organizations, known as Notified Bodies for safety, are third parties for product certification in the EU. VDE, TUV, and Demko are examples of EU Notified Bodies. Nationally Recognized Testing Laboratories (NRTLs) are sanctioned by the Occupational Safety and Health Administration (OSHA) for certification of products in North America. UL and CSA are NRTLs. Table 1 shows examples of safety conformity marks.

The product manufacturer/supplier ultimately is liable for product safety. But a safety mark can enhance a company’s sales and limit the manufacturer’s risks should the product’s compliance come into question.

At first, certification may seem complicated. But once you establish a working relationship with a test and certification body, the rewards of certification marks are seen through increased customer confidence in your products.

CE Marking

Since the introduction of the CE Marking as a mandatory requirement in Europe, past barriers to trade have been lowered, but the public’s confusion surrounding the meaning of the mark persists. In addition, market-surveillance audits show that many products bearing only the CE Marking often do not meet the directives. Consumers are beginning to question the CE Marking, especially as it relates to product safety and due diligence.

The European Conformity (CE) Marking is the manufacturer’s or importer’s self-declaration (self-test) symbol signifying that a product meets applicable EU directives and standards. The CE Marking is for customs authority control, allowing products to circulate freely within Europe.

The CE Marking is the supplier’s self-declaration marking for EMC and safety. It allows products to be placed on the market and ensures the free movement of goods, and it encourages authorities to audit and withdraw nonconforming products. It is not a third-party approval, certification, safety mark, or quality mark; it is not appropriate for most components; and it is not intended for sales or marketing purposes.

Due diligence means taking all reasonable steps to ensure conformity. Proving due diligence is difficult under the CE Marking approach. Even though it’s the manufacturer’s or importer’s responsibility, customers have the right to ask if safety conformity was verified by a certification body. Safety marks on products are the manufacturer’s best defense of due diligence should a product’s conformity come into question.

Product Classifications

Several safety classes relate to test and measurement products depending on the product’s working voltage or rating and the operating environment. The classifications that follow apply internationally.

Measurement Category

The measurement category, also referred to as the installation category, establishes standardized impulse-withstand voltage levels that may occur in an electrical distribution system. Figure 1 depicts the correlation of parts of a building to measurement category. Higher measurement categories mean larger spacing distances on PCBs and, often, larger components. The following definitions are based on IEC 61010-1:

  • Measurement Category I—The most benign category with less severe transients. CAT I is for measurements on circuits not directly connected to the AC supply wall outlet such as protected secondaries, signal level, and limited energy circuits.

  • Measurement Category II—For measurements performed on circuits directly connected to the electrical distribution system such as provided by a wall outlet (115/230 VAC). Examples are measurements on household appliances or portable tools.

  • Measurement Category III—For measurements performed in the building installation at the distribution level such as on hardwired equipment in fixed installation and circuit breakers.

  • Measurement Category IV—For measurements performed at the primary electrical supply (<1,000 V) such as on primary overcurrent protection devices, ripple control units, or meters.

Pollution Degree

Conductive dust or moisture can reduce the surface resistivity and voltage-withstand capability of materials, increasing the potential for voltage arc-over. Pollution degrees measure the insulation capability of plastic materials or insulators based on the amount of conductive dust, ionized gas, and moisture. A higher pollution degree translates into larger PCB spacing distances and components. Offices generally are a degree 2 environment. Some industrial areas are degree 3.

  • Pollution Degree 1—No pollution or only dry, nonconductive pollution which has no influence.

  • Pollution Degree 2—Normally only nonconductive pollution or temporary conductivity caused by condensation.

  • Pollution Degree 3—Conductive pollution or dry, nonconductive pollution which becomes conductive due to condensation.

Part 2

Part 2 of this article focuses on the underlying safety principles needed to design products that are not hazardous to the user. It includes a handy design checklist that outlines important safety considerations for enclosures; grounding, wiring, and connections; labels and markings; and flammability of materials. Part 2 will appear in EE’s December issue.

About the Author

David Lohbeck is a senior safety engineer at National Instruments. Previously, he worked for Motorola, Memorex, Dell, and TUV in the field of international product safety and EMC. Mr. Lohbeck is the author of the CE Marking Handbook: A Practical Approach to Global Safety Certification. He received a B.S. from Arizona State University and an M.A. from the University of Phoenix. National Instruments, 11500 N. Mopac Expressway, Bldg. C, Austin, TX 78759, 512-683-8474, e-mail: [email protected]

FOR MORE INFORMATION

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Published by EE-Evaluation Engineering
All contents © 2003 Nelson Publishing Inc.
No reprint, distribution, or reuse in any medium is permitted
without the express written consent of the publisher.

November 2003

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