The Dielectric Voltage Withstand Test is a test known by many names including the Dielectric Test and the Hipot Test. This is the most common test of all product safety tests - performed by certification labs as part of all Certifications and also performed by electrical product manufacturers on 100% of production. Let’s review the elements of this test:
Purpose of the Test:
a) Mains to Ground insulation is tested at the product’s mains connection = the plug on the cord or, the field wiring terminals for the mains conduit connection. This is also a commonly required production line test. As such, many production hipot testers are designed to allow cord connected units to plug directly into the hipot tester.
b) Isolating components such as transformers, opto-isolators, and relays are also tested from mains to secondary if they isolate a user accessible circuit.
c) Dielectric testing individual insulating materials requires a special test stand defined by the standards that holds the material being hipot tested with minimal force and rounded ends to prevent damaging the insulation or affecting the test results.
d) The test is typically specified as an AC test voltage. However, if the product being tested has EMI filtering components for EMC compliance purposes, it will not pass an AC dielectric. The capacitors to ground (Y caps) will leak excessive current with an AC test voltage, to such an extent that it usually prevents reaching the test voltage – attempting to turn up the voltage will only cause more current to flow. If you are using a production dielectric tester, it will usually trip and indicate a false test failure. However, this is not a test failure because the current flow is not caused by insulation failure. In fact the capacitor is operating as intended, although the excessive current flow from attempting an AC dielectric test is likely to damage the capacitor. The solution is to test with a DC test voltage, at a test potential equal to the peak of the specified AC test voltage (1.414 x AC voltage).
e) This test requires additional user precautions and preparation due to high voltage. Perform this test on an insulating surface. Stand back! DO NOT touch the product under test while the high voltage is being applied. Failure of the product’s insulation system during testing could cause anyone touching the product when this occurs to receive an electrical shock.
Test Objectives: The objective of the Hipot Test is to verify that the electrical insulation used to protect the user from a Risk of Shock is suitable for the application. Testing is used to identify any failure of the product insulation system that could lead to a shock hazard to the user. The detailed objectives include:
As you can see, we don’t simply perform the tests because they are in the standard. Each test in the standard has a set of objectives that relate to the 6 Hazards of Product Safety. The Dielectric Voltage Withstand Test is performed as part of the Risk of Shock compliance review. Verifying reliability of the product’s electrical insulation system is crucial to insuring it continues to provide protection from a Risk of Shock, a potentially serious hazard that could lead to death by electrocution. It is therefore a very important test – another test that directly saves lives. This is why the Production Dielectric Voltage Withstand Test is required on 100% of certified products.
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