Testing transformers, generators or motors can be dangerous because of inductive kickbacks. These currents are generated when a current is applied in an inductor and the circuit is opened. The collapsing magnetic field in the coil induces current. This current spike can be higher than the original which can cause an electric shock.
It is important to understand the safety precautions that need to be taken when testing highly inductive devices. The tools used for testing transformers and motors are a DLRO and a winding resistance test. Both tools conduct the same test. However, a microOhmmeter doesn’t have protection circuits for inductive kickback. Suddenly disconnecting the microOhmmeter from the winding can cause a serious electrical shock.
For more information about safety precautions and the basics of testing winding resistance in transformers and other inductive loads, you can read this article from Thomas Sandri.
Low Resistance Ohmmeter or Winding Resistance Test Set… What’s the Difference?
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