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Using AC Sources for Compliance Testing

Introduction
Due to international safety agency standards, electrical safety tests are an essential part of the design and manufacturing process if a company wishes to sell products into the EU or affix a safety agency mark to their products for sale domestically. Dielectric withstand (hipot) testers are perhaps the most commonly used instruments, as international safety agency specifications usually call for a hipot test to be performed as a 100% production line test. Other instruments are used to perform tests including the Ground Bond test, the Insulation Resistance test, and the Leakage Current test. While most if not all manufacturers perform these types of tests on the products they manufacture, many mistakenly forego the purchase of an AC power source and rely on utility power or an inexpensive variable transformer to power their products during compliance testing. Failure to use an AC power source can oftentimes result in an improper test setup or worse, noncompliance. In fact, in order to comply with many international standards that call for a Leakage Current test or a functional run test, an AC power source must be used during testing.

Shortcomings of Traditional Power Alternatives
Traditional power alternatives such as utility power and variable transformers have several shortcomings that make them less than ideal for compliance testing. Perhaps the most obvious is that utility power output is fixed and unregulated. Therefore, manufacturers that rely on utility power for compliance testing are not accurately following testing procedures. As we will discuss below, most standards call for products to be tested at 110% nominal line voltage. With no way to adjust the output voltage of utility power, manufacturers cannot comply with this specification. Further, many international standards call for testing to be performed at the nominal operating frequency of the product. In the case of the EU, this is 50 hertz. A manufacturer in the US cannot simulate this output specification simply by plugging their product into a standard 60 hertz wall outlet and therefore cannot meet the test specification.


A common alternative to utility power is to use a simple variable transformer to step up the voltage to 110% of the nominal condition. While a variable transformer will perform this function adequately the operator usually has no way to accurately monitor the exact output voltage and current without additional metering equipment. Relying on additional equipment can be tedious, expensive, and further complicate the test setup while leaving more room for operator error. A variable transformer also fails to meet the 50 hertz specification that many standards call for, effectively prohibiting manufacturers from testing their products for shipment overseas to the EU.

Real World Examples
Most electrical safety testing standards call for verification of the DUT’s insulation and the continuity of the ground circuit in order for the product to receive a safety agency listing or the CE mark of conformity. Yet there are a variety of standards that call out for a functional test or a Leakage Current test in order to determine if the product is operating within nominal limits. The following example is taken from the Medical Device standard IEC/UL 60601-1 3rd Edition.


8.7 LEAKAGE CURRENTS and PATIENT AUXILIARY CURRENTS
8.7.1 General requirements

  • a) The electrical isolation providing protection against electric shock shall be of such quality that currents flowing through it are limited to the values specified in 8.7.3.
  • b) The specified values of the EARTH LEAKAGE CURRENT, the TOUCH CURRENT, the PATIENT LEAKAGE CURRENT and the PATIENT AUXILIARY CURRENT apply in any combination of the following conditions:
  • - at operating temperature and following the humidity preconditioning treatment, as described in 5.7;
  • - in NORMAL CONDITION and in the SINGLE FAULT CONDITIONS specified in 8.7.2;
  • - with ME EQUIPMENT energized in stand-by condition and fully operating and with any switch in the MAINS PART in any position;
  • - with the highest RATED supply frequency;
  • - with a supply equal to 110 % of the highest RATED MAINS VOLTAGE


Note above that the highlighted specification calls for the DUT to be operated at the nominal frequency at 110% of the rated voltage. Oftentimes variable transformers don’t include a voltage meter accurate enough to confirm whether or not this specification is being met. Utility power also fails to satisfy this requirement if the product is to be sold in the EU. Further, neither of these alternatives carry a CE mark (which is often required on all test equipment used for testing products to be sold in the EU). For customers that are looking to satisfy these types of specifications, but have a more advanced automated test area, the EEC 8500 series of programmable AC power sources is the ideal choice. These automated sources will satisfy even the most demanding compliance testing applications and can controlled with a PC via a variety of communications interfaces such as USB, Ethernet and GPIB.

Figure 1: EEC 8500 Series Programmable AC Power SourceFigure 1: EEC 8500 Series Programmable AC Power Source

Figure 1: EEC 8500 Series Programmable AC Power Source

Exclusive EEC Benefits for Compliance Testing

EEC’s line of AC power sources is ideal for satisfying a wide variety of compliance testing applications. Perhaps one of the most beneficial features of EEC power sources is their compatibility with Ikonix electrical safety testing equipment. When used in tandem, EEC AC power sources along with Ikonix electrical safety testers can provide an efficient, no-hassle test system that fully complies with most international compliance testing standards while reducing test setup complexity and increasing productivity. EEC power sources will function in a dedicated main/secondary relationship with Ikonix electrical safety testers to provide the necessary DUT power during hipot testing, Leakage Current testing, and functional Run testing.

Conclusion
While electrical safety testing equipment is quite common in the production area, many manufacturers fail to realize the benefits that an AC power source can provide to them during compliance testing. Not only will using an AC power source increase productivity and save bench space by eliminating the need for other equipment, but also ensure that the production facilities test setup and methodology are compliant with international standards. While shortcuts in test systems setups may be appealing, the cost of an audit or accidental customer injury are far worse than the short-term benefit gained by using traditional power alternatives like a variable transformer or utility power. For these reasons, an AC power source is a welcome addition to any electrical product manufacturer’s production area.