In most of television receivers, the mains is isolated by an isolating transformer. However, a RC-unit (i.e., two 5.6M ohm resistors in series and connected parallel with a 0.022uF capacitor) is connected between accessible parts and mains. What is the primary function of this RC-unit?
According to sub-clause 10.3 "Insulation resistance and dielectric strength" of EN 60065, the tests can be done with disconnection of the RC-unit. In type test, the test should not impose any problem but in production, the RC-unit cannot be practically disconnected on finished products before the tests take place. Insulation resistance and dielectric strength tests are ones recommended by most approval agencies such as BEAB, UL, CSA, etc. In general practice, the RC-unit is not disconnected and select a higher trip current, i.e. 5 or 10 mA on the withstanding voltage tester. Why does the standard require the disconnection of RC-unit for the tests? Is there any deviation from the spirit of the standard in the production tests? In sub-clause 9.1.1 "General - Accessible parts shall not be live" of EN 60065, should the RC-unit be disconnected on the leakage current measurement? What is the impact on the true leakage current of the insulation with the RC-unit? Appreciating any guidance. Raymond Li Dixons Asia Ltd.
