Electrical safety testing
Electrical safety testing is essential to ensure safe operating standards for any product that uses electricity. Various governments and agencies have developed stringent requirements for electrical products that are sold world-wide. In most markets it is mandatory for a product to conform to safety standards promulgated by safety and standard agencies such as UL, CE, VDE, CSA, BSI, CCC and so on. To conform to such standards, the product must pass safety tests such as the high voltage test (also called as Dielectric voltage-withstand test or high potential test), Insulation Resistance Test, Ground (Earth) Bond & Ground Continuity Test & Leakage Current Test (also called as Line Leakage Test, Earth Leakage Current Test, Enclosure Leakage Current Test or Patient Leakage Current Test). These tests are described in IEC 60335, IEC 61010 and many other national and international standards.
In general, IEC 60335 is the most widely applied standard for electrical safety testing, especially for domestic appliances. Many safety testing standards in the world have been based on it. To safeguard workplace health and safety, many sections of the Occupational Health and Safety Regulation provide guidelines on electrical safety and the appropriate equipment required to work on low and high voltage electrical appliances.
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High Voltage Test (Dielectric Voltage-withstand Test)
This test is carried out by applying a significantly higher than operating voltage to the device under test. In this test, the insulation of a product, stressed to a greater extent than under normal operating conditions, should not be breached for the product to pass. In most cases, the device is stressed to twice its normal operating voltage. During type testing, i.e. testing during designing a product or for a double insulated product, however, much larger voltage may be applied. For all electrical products, the high voltage test is a universal test, meaning that every unit should pass before it can be used.
Insulation Resistance Test
This test is to measure the total resistance of a product’s insulation by applying a voltage of 500V – 1000V for low voltage systems. The minimum acceptable value of resistance for a product to pass an insulation resistance test is 1 mega Ohm (1000 kohms). The insulation resistance test is not a substitute for the high voltage test. Many standards and safety agencies have specified this is a universal test for all products. This test may also be carried out after every maintenance procedure or repair.
Earth Continuity Test
This test is performed by measuring the resistance between the third pin (ground) and outside metal body of the product under test. The maximum acceptable value is generally 0.5 ohms although certain standards may specify 0.1 ohms. This test is generally carried out at a slightly higher current (e.g. 25-60A) so that the ground bond circuit maintains safe voltages on the chassis of the product, even at a high current, before the circuit breaker trips. This test is essential so that the product does not cause an electric shock resulting from insulation failure.
Leakage Current Test (Line Leakage Test)
This test is to measure the undesirable leakage current that flows through or across the surface of the insulation or the dielectric of a capacitor. This test is generally carried out at 100%-110% of the rated input voltage of the product under test. The maximum acceptable limit of a leakage current is generally 210 micro amperes. At first, this test was mandatory for medical devices only.
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