The TRM-403 is a  three phase transformer winding resistance meter that allow the user to connect all test cables to the transformer bushings. The unit will then measure the transformer resistance value for each of the phases without the need to disconnect and reconnect cables for each phase. The TRM-403 can provide a fast and stable reading of very large transformers by utilizing a 60Vdc power supply. It is capable of outputting a selectable test current from 1A to 40A. Since the TRM-403 can accurately measure resistance from 1 micro-ohm to 500 Ohms, it can be used as a micro-ohm meter to measure EHV circuit breaker contact resistance, or for any low resistance measuring application.