Many questions arise about the Low-Voltage Directive, its product safety requirements, and the CE Marking. What do they mean to a manufacturer of electrical and electronic products, and what is necessary to comply?
The Low-Voltage Directive
The Low-Voltage Directive (LVD) 73/23/EEC, a council directive dated February 1973, provides a single set of requirements and a single approval for many countries in the European Community (EC). Article 2 of the Low-Voltage Directive states:
“The Member States shall take all appropriate measures to ensure that electrical equipment may be placed on the market only if, having been constructed with good engineering practices in safety matters in force in the Community, it does not endanger the safety of persons, domestic animals or property when properly installed and maintained and used in applications for which it was made.”
The directive also indicates that harmonized product safety standards must be drawn up by common agreement between the bodies notified by the Member States. It also shall be kept up to date in the light of technological progress and the development of good engineering practice in safety matters.
Any electrical products designed for use with a voltage rating of between 50 V and 1,000 VAC and between 75 V and 1,500 VDC must comply with these unified standards if the products are to be marketed in the EC after Jan. 1, 1997. The following equipment is exempt from the directive:
Electrical equipment for use in an explosive atmosphere.
Electrical equipment for radiology and medical purposes.
Electrical parts for goods and passenger lifts.
Electrical meters.
Plugs and sockets outlets for domestic use.
Electric-fence controllers.
Radio-electrical interference.
Specialized electrical equipment used on ships, aircraft, or railways, which comply with the safety provisions drawn up by international bodies in which the Member States participate.
Prior to the LVD, if a company wanted to sell electrical products into the United Kingdom, its products had to be approved by the government-approved agency, the British Standards Institute. If they wished to market the same products in Germany, they had to be constructed and approved under VDE or TÜV safety standards established by the Association of German Electrical Engineers.
The safety-agency standards and test methods differed from one country to another. This complicated the safety approval process since one agency would not recognize the test data from another.
Under the LVD, harmonized safety standards provide one certification to comply with and be recognized by all members of the EC. This achieves one of the goals of the EC—to provide a standardized means of allowing commerce between member countries.
However, the LVD is not an all-encompassing standard that covers all electrical products. The harmonized product safety standards of the LVD typically are selected from the International Electrotechnical Commission (IEC) or the regional body CENELEC European Norm (EN) standards.
Like the Underwriters Laboratories in the United States, these standards cover product safety related to the operator and the user. They help ensure that products are constructed following good engineering practices and that appropriate tests are performed on the product certifying that the safety requirements have been met.
A Technical Construction File must be maintained on the product, which contains applicable test and technical data on the product’s conformance. If these requirements are met, the manufacturer then may prepare a Declaration of Conformity. The Declaration of Conformity must accompany each shipment the manufacturer makes. This signals to the receiving country that the products have met the requirements of the LVD and then may have the CE Marking applied to them.
Product Safety Requirements
Since the product safety requirements differ from one specification to another, let’s examine one specific product, a computer monitor, to identify some of the typical tests and how they are performed.
First, the computer monitor must be designed and tested in accordance to the European Norm Standard EN 60950 Standard Safety of Information Technology Equipment Including Electrical Business Equipment. The product must be designed and constructed to protect the user from electrical shock and serious injury from fire originating in the equipment under normal use and under likely fault conditions.
Where safety is involved, components and subassemblies chosen for use within the monitor must comply with the safety aspects of the relevant IEC or EN component standards. All components shall be checked for correct application and use in accordance with their ratings. They must be subjected to the applicable tests of this standard as a part of the equipment with the exception of those tests that are a part of the relevant IEC component standard. A component not certified for compliance with a relevant standard shall be checked for correct application and use at its specific rating.
EN 60950 specifies performance or type tests on a representative sample of the product to determine if it, as designed and manufactured, can meet the requirements of the standard. All of the tests are designed to ensure the safe operation of the product.
The routine or production tests are detailed in the EN 50116 Standard Information Technology Equipment, Routine Electrical Safety Testing in Production. It defines the tests that must be performed on each device during or after manufacture to detect manufacturing failures or unacceptable tolerances in manufacturing and materials.
Three of the most common electrical safety tests are specified under EN 60950. The ground-bond and dielectric-withstand tests are routine production-line tests under EN 50116.
Ground-Bond Test
This test verifies that the resistance between accessible parts required to be reliably grounded for safety reasons and that the protective grounding terminal or grounding contact is not greater than 0.1 W . A properly grounded product provides a necessary level of protection should the first protection level—the insulation—fail.
The test current should be 1.5 times the current capacity of any hazardous voltage circuit at the point where failure of the basic insulation would make the grounded part live. The test voltage must not exceed 12 V, and the test current can be either AC or DC but should not exceed 25 A.
The voltage drop between the protective ground terminals or ground contact and the part to be grounded is measured, and the resistance is calculated by measuring the voltage drop. The resistance of the protective grounding conductor of the power supply cord should not be included in the resistance measurement.
This test is specified as both a type test and a routine production test that must be performed on every product. Figure 1 shows a diagram of how the test is performed.
Leakage Current Test
Figure 2 shows the test circuit for performing the ground leakage test on a single-phase product, such as the computer monitor. The measuring instrument is switched in each position, and the readings are recorded for each position of all primary power switches that control the input power to the device under test.
Depending on the type of equipment being tested, the maximum allowable leakage currents can range from 0.25 mA for Class II (double-insulated) products to 3.5 mA for stationary products permanently connected to a power source. The leakage current readings obtained during this test primarily are related to the design of the instrument. This test is not required as a routine production-line test under EN 50116.
Dielectric Strength Test
This test usually is referred to as a hipot or dielectric-withstand test. It checks the electric strength of the insulating materials used within the product being tested. The test is performed by applying a sinusoidal AC voltage of at least 1,000 V for basic or operational insulation or 3,000 V for reinforced insulation at a frequency of 50 Hz or 60 Hz. The specification also allows a DC voltage equal to the peak of the prescribed AC test voltage to be used.
The type or performance test specified in EN 60590 requires that the voltage be raised gradually from zero to the prescribed test voltage and held there for 60 s. There cannot be any indication of breakdown during this test.
EN 60590 defines insulation breakdown as that which occurs when the current flowing as a result of the application of the test voltage rapidly increases in an uncontrolled manner, and the insulation does not restrict the flow of the current. Corona or single momentary flashover is not insulation breakdown.
For routine or production-line tests, the test voltage must be applied between the primary and accessible conductive parts, excluding secondary circuits, and must be maintained for at least 1 s but not more than 6 s. The potential must be at least 1,500 VAC for basic insulation and 3,000 VAC for reinforced insulation.
Basic insulation is defined by IEC as the insulation that provides basic protection against an electrical shock. Reinforced insulation is a single system that provides a degree of protection against an electrical shock equivalent to double insulation.
Insulation breakdown for production test is any significant increase from the steady-state current measured during the test. The hipot tester must indicate the test voltage and the insulation breakdown, either with an audible or visual indicator. The trip current level is determined by the manufacturer of the product under test.
Under EN 50116, the manufacturer must maintain a file with this data for all equipment tested once a product conforms to the safety requirements of the LVD:
Date of the test.
Model and serial number of the equipment.
Value of ground circuit resistance with the corresponding current value.
Value of the voltage applied during the dielectric-withstand test.
Quick reference information that the whole set of tests has or has not been successful.
The requirement for recording test data has made safety-testing instruments with computer interfaces very popular. By using a PC to control the safety tester, all test data automatically is stored in an electronic format at the end of every test.
CE Marking
After a manufacturer has performed the required tests, the CE Marking can be applied to the product and the packaging. But what does this mean? The CE Marking on a product is the manufacturer’s or importer’s self-declaration mark of conformity, indicating compliance with all applicable directives such as safety and EMC.
Products that comply with all the relevant directives can bear the CE Marking. The deadline for compliance to the EMC directive was Jan. 1, 1996; the deadline for compliance to the LVD was Jan. 1,1997.
Conclusion
Harmonization of standards can be a benefit to electrical manufacturers by providing a clear understanding of what tests must be performed. Customers now are assured that the products they purchase have been tested and conform to specified safety requirements.
About the Author
Dwayne M. Davis is the technical services manager heading the Technical Support Group at Associated Research. For more than 20 years, Mr. Davis has been involved in the design, development, and manufacture of the company’s high-voltage products. He holds an electronics degree from DeVry Technical Institute. Associated Research, 905 Carriage Park Ave., Lake Bluff, IL 60044, (847) 295-3312.
Copyright 1997 Nelson Publishing Inc.
August 1997
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