The TWA-TRT safety switchbox is an optional accessory for TWA and TRT series instruments, which share the common test leads. It ensures the safety of the operator during the change of test leads from one instrument to the other by safely grounding the test leads during this change.
The TWA and TRT instruments together with this accessory enable the measurement of three-phase transformer winding resistance, turns ratio, excitation current, phase angle, magnetic balance, and also to detect the transformer vector group and safely demagnetize the transformer. All these tests are done with a one-time connection and disconnection to 6-8 transformer terminals. There is no need to change any connections on the transformer between any of these tests. All changes of connection can be safely performed on the ground.