Is an isolation transformer required for leakage current testers?

QWhy are isolation transformers used in leakage current measurements of medical and general electrical equipments? (Leak Current HiTester ST5540)


In order to measure leakage current accurately and safely.

1. The N (neutral) of a commercial power supply has a electric potential of several volts due to the effect of wiring impedance and the leakage current of equipment connected to that system. This electric potential difference results in an error, and accurate leakage current values cannot be obtained.
Therefore, connect the N side to the ground to prevent measurement errors.

2. If an unexpected current flows during the test due to a failure of the device under test, there is a possibility that the earth leakage breaker may drop.
In such a case, other electrical equipment used in the same facility will also be turned off, which may lead to a major accident.
However, when an isolation transformer is used, the leakage breaker and the device to be measured are isolated from each other. If the device under test were to malfunction, the earth leakage breaker would not trip and other equipments would not be affected.

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