In addition to stringent physical and electrical tests and inspections at all stages of manufacturing, every transformer, with its primary and secondary leads and connectors, is immersed in water while hot. A 15,000 volt direct current insulation resistance test is performed on the primary, and 5,000 volts DC on the secondary (non-earthed transformers only). A ratio check is also conducted during the final stages of testing. Nominal leakage current to earth during the 15,000 volt DC test is <0,1 micro amp (hot).
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