isolation transformer measurement
Most of the transformers in wall adapters (which stepdown 110/220VAC to 1.5 or 3, 4, 6, 9, 12, 15, 24V) are ISOLATION transformers, where the primary and secondary windings are isolated from each other.
Most of the transformers that are used for the purpose of mains voltage regulations such as 220V:110V stepdown, AC voltage regulators are NON ISOLATION transformers, where secondary winding is a part of primary winding.
However, when people talks about the ISOLATION transformers, they mention about the 1:1 transformer with seperate identical primary and secondary windings. They supply the mains voltage at secondary winding. This kind of transformer is used for safety purpose.
You may know that mains lines in our houses have the L (line) terminal and the N (neutral) one. The N terminal is grounded at the power transformer station. That is why when you touch the neon bulb electric tester tip to the L terminal, the neon bulb lights, and to the N terminal, the neon bulb does not light. And when you stand on ground but touch the L terminal, you must be electrically shocked.
The isolation transformer now supplies the mains voltage, but not any of its terminal is grounded, so it is safe for you when touching to one of its terminals.
Of course, the transformer must be blown when you shorten the secondary termicals if there is not any suitable fuse or circuit breaker at primary and secondary sides. You must use suitable fuses or circuit breakers at both sides of the isolation transformer, or at least the primary side.
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