The WRT-10 by NDB Technologies is a winding resistance tester which is designed for power transformer and large motor applications. This tool can perform winding resistance testing which is an important process in regulating the complete function of power transformers so that it guaranteed quality beyond its performance. The testing is crucial to transformers and large motor because they are always subjected to vibrations, overloading and fluctuating large temperature. Another factor which is a critical element in power system is the tap changes. Using this tool, it can detect all the changes that the tap changer had made in the system. The unit works by injecting a DC current using windings and measuring the voltage drop. Also, it calculates resistance through a formula of R = E / I.