Product safety certification—which users have come to expect in electrical products in North America—also is the first step on the road to compliance for information technology equipment (ITE) manufacturers. Yet, it is not just an easy, rubber-stamp operation to qualify a product for the market.
In the United States, electrically based products must be listed by a Nationally Recognized Testing Laboratory (NRTL) or the manufacturer could be hit with a hefty fine. Although you can obtain information about U.S. and Canadian safety requirements in the binational standard UL 1950/CSA C22.2 No. 950-95, do you know what you as the manufacturer can do to ensure your products will comply before you go to an NRTL?
Advanced planning is the best recommendation for achieving product safety certification, said Tom Else, laboratory director for product safety at Northwest EMC. Consider safety issues from the earliest stages of design. Companies planning to market products here or abroad should think about a preliminary design review with a consultant or testing lab.
Another helpful strategy uses the risk-analysis process in the design stage, said Mr. Else. The risk-analysis process evaluates the overall product and identifies any large or significant safety risks. The evaluation should indicate the likeliness, severity of the event, the risk type, and how it can be controlled. Risk analysis is a requirement for the product’s technical file. “Undergoing a risk analysis before production results in a superior, safer product,” he added.
To help obtain safety approval, your product should be classified according to category and then the specific standard, said Eric Tenody, product safety manager for Instrument Specialties. If the product will be marketed internationally, obtain a list of the appropriate certification programs and agencies for those foreign countries.
Armed with this information and details such as electrical specifications, intended use, and a sample, the manufacturer and the lab can step through a constructional critique that highlights noncompliance areas, continued Mr. Tenody. This gives you a good indication if the essential safety requirements were designed into the product.
To assist in obtaining a safety approval, Pryor McGinnis, president of Compliance Test Laboratories, recommends that you:
Select the appropriate standards and directives for the end product and marketplace. If you are uncertain, consult the appropriate agency or a testing house. Become intimately familiar with the requirements and apply them to the product design.
Consider using the Certified Body (CB) Scheme, the international approval procedure, if the product is targeted for outside North America. A CB certificate and test report will help gain entry into numerous countries around the world.
Select components and modules suitable for the intended application. Critical parts should be UL listed or recognized and certified by CSA and a European safety agency. Critical components are defined as those used in the primary circuits such as EMI filters, fuses, and transformers; internal wiring; interconnecting cables, and interlock switches. Obtain documentation from the manufacturer that verifies agency approval of critical components.
Use materials such as plastics with the correct flame ratings. Have the supplier mold the plastic identification into the part to facilitate follow-up inspections.
Design the markings, labels, and symbols in accordance with the requirements of the applicable standard.
Include safety-related instructions, information, and statements in the user manual in accordance with the requirements of the appropriate standard.
Translate user manuals into the language of the country where the product will be marketed.
When preparing to obtain a safety certification, choose your certifier with care and be ready to make the necessary changes to meet regulation requirements, said Ken Boyce, engineering group leader at Underwriters Laboratories. The certifier is the subcontractor in the product development cycle, and the manufacturer must be confident of the certifier’s qualifications.
A qualified provider has the resources and experts on staff to complete the product safety checks, said Mr. Boyce. The provider should be on top of any changes in requirements and continually refine the services to meet the evolving needs of the customer.
To significantly expedite the certification work, provide information on the target markets and schedules for the certifier, said Mr. Boyce. UL has found that open communications in the design phase, use of thorough preliminary investigation reports, and interactive preparatory training make the evaluations more efficient.
To minimize the risk of noncompliance late in the development cycle, the manufacturer also should review the requirements before submitting a product for certification, added Mr. Boyce. A complete list of safety-critical components, including alternate vendors, schematics, samples, and instruction manuals (preferably draft versions), should be supplied as soon as possible.
When you have incorporated safety designs and know the required safety agencies you are ready to create a comprehensive test plan, said Instrument Specialties’ Mr. Tenody. Find out what basic tests are needed and the specific details to focus on, such as an awareness of temperature limits for components, isolation and magnetic barriers, and insulation requirements. Determine your needs for normal and abnormal conditions, any excessive leakage currents, potential shock and energy hazards, and
deliberate abnormal fault conditions such as overloads of power-supply circuits.
If the product is destined for the international marketplace, also coordinate the EMC requirements for radiated and conducted emissions and immunity, said Rod Morgan at National Technical Systems (NTS). Changes or the addition of components to meet RF requirements can adversely affect product safety if they are not properly coordinated.
Recommended Tests
The applicable construction and performance requirements for your products are contained in the relevant safety standards, said UL’s Mr. Boyce. The facility demands, equipment specifications, and test methodology also will be based on these requirements.
For any company developing product lines, it makes sense to have the resources to perform appropriate preliminary testing for its products, added Mr. Boyce. It will give the company a clear edge in identifying potential problems and prevent an impact on the production process.
The product requirements in the standards also dovetail with installation requirements, such as the National Electrical Code and those demanded by the European Union. The challenge for many manufacturers, especially when exporting their product, is to identify all the relevant standards. A full-service certifier can help you find the correct standards and generate test reports that are acceptable to other certification bodies.
Several tests for ITE, said CTL’s Mr. McGinnis, should be conducted by the manufacturer before the products are submitted to the appropriate regulatory agency:
Input Current—Generally, steady-state input current cannot exceed rated current by more than 10%.
Capacitor Discharge—There should be no risk of electric shock from stored charges on capacitors connected to the power line circuit. The discharge circuit for capacitors exceeding 0.1 µF must have a time constant not exceeding 1 s for plug-in equipment that connects to the building supply via nonindustrial plugs and socket outlets or appliance couplers.
For permanently connected and plug-in equipment intended for connection to the building supply wiring via industrial plugs and socket outlets, the time constant must not exceed 10 s. Additionally, voltage must decay to 37% of the original value within one time constant.
Ground Continuity—Resistance between the protective earth terminal and the parts that must be grounded to earth must not exceed 0.1 W . The test current must be 1.5 times the current capacity of any hazardous voltage circuit at the point where failure of basic insulation would make it a live part. Test voltages must not exceed 12 V; and the test current can be AC or DC, but not more than 25 A.
Stability—Under conditions of normal use, equipment must not become physically unstable or a hazard to operators. Specifically, the unit must not lose balance when tilted to an angle of 10° from upright. The unit must not lose balance when a force equal to 20% of the unit’s weight but not more than 250 Newtons is applied in any direction except upward and not exceeding 2 m from the floor.
Leakage Current—Equipment must not have a ground leakage current that exceeds 0.25 mA for Class II products; 0.75 mA for Class I hand-held, 3.5 mA for Class I movable but not hand-held, 3.5 mA for Class I stationary, plug-in Type A equipment, and 3.5 mA for Class I stationary, permanently connected or plug-in Type B equipment.
U.S. vs European Standards
In the United States, the Occupational Safety and Health Act helped create the laws for a safe work environment. The laws are found in the Code of Federal Regulations, Number 29. These volumes detail the qualifications for an NRTL such as UL or CSA. The laws also mandate that an employer use electrical devices that are certified as safe by an NRTL. This means that the responsibility lies with the employer, not the manufacturer, to find and use certified safe equipment.
Product safety in the European Union is covered under the Low-Voltage Directive (LVD), said Mr. Morgan of NTS. The terminology is somewhat deceiving because low voltage means 1,000 VAC or less. For ITE, the safety standard is the European Union’s EN 60950 document, which refers to IEC Publication 950 Safety of Information Technology Equipment, Including Electrical Business Equipment.
Products evaluated to North American standards that existed prior to the harmonization of IEC-based documents generally do not comply with the European EN-standards for the LVD, said Mr. Tenody from Instrument Specialties. Although the LVD has been in place since 1973, its enforcement through the CE-Marking process has put many North American manufacturers in a dilemma, struggling to design products for these sometimes more stringent requirements.
The ITE requirements for North America fortunately have harmonized the U.S. and Canadian versions, which resulted in the binational UL 1950/CSA950 version. A transitional period was implemented for North American manufacturers to partially comply with the IEC 950 product safety document while still using the older, less stringent UL/CSA requirements.
The latest version of the binational document has only a few deviations from the IEC-950, continued Mr. Tenody. For example, the use of approved Class 2 power supplies per CSA223/UL 1310 or transformers per CSA66/UL 1585 does not necessarily meet the EN 60950 requirements.
The basis by which these components are proven to be safe by the North American standards is very different than the IEC-based philosophy. There are contrasting constructional requirements with differing temperature limits that result in a different criteria for a fire hazard.
Because the CE Marking indicates conformance to all the applicable EN Directives, conformance to EN 60950 typically is a major element toward the CE Marking, said UL’s Mr. Boyce. However, some countries in the EU have their own national deviations, relevant only within that country.
UL 1950 has code differences and component and telecommunications deviations when compared to either the IEC or EN safety regulations, said Mr. Boyce. The North American code requirements that affect the electrical connection to the power lines are more stringent than the European counterpart. Safety-critical component requirements that are more severe in North America must conform to the U.S. or Canadian version rather than the European regulations. Telecommunications product safety also is more stringent in the United States and Canada than Europe.
A manufacturer and importer must sign a Declaration of Conformity to gain access to an EU country. A certified product safety lab is not mandated, and a manufacturer may declare compliance without using an internationally certified lab. Typically, however, manufacturers will obtain international certification to show due diligence to prevent any challenges to the validity of their CE Marking.
Acknowledgments
These companies provided information for this article:
Compliance Test Laboratories……………………(864) 843-1604
Euro EMC Service………………………….(011) 49 3328 430 141
Instrument Specialties……………………………….(717) 424-8510
National Technical Systems……………………….(818) 591-0776
Northwest EMC………………………………………..(888) 364-2378
Underwriters Laboratories………………………….(847) 272-8800
Wyle Laboratories…………………………………….(205) 837-4411
Copyright 1998 Nelson Publishing Inc.
May 1998