The measurement of the winding resistance in a running three-phase motor with the ELETTROTEST Resistance Meter requires some precautions since the single phases can influence each other reciprocally.

Typically, a 2-channel resistance meter is used, with 3 inlets and 3 outlets for power supply (for decoupling) and two measurement channels (RHM1 and RHM2), each made up of two injection (INJ) and reading (SENSE) terminals.

The measurement requires injection on the load and reading in two possible points: on the load (measurement at 4 wires)
or directly on the instrument (measurement at 2 wires).
The choice of one measurement or another depends on the type of precision you want to have, as well as the connections available. In the case of a 2-wire measurement, the value to be read also includes the resistance of the connection cables, and in the case of a 4-wire measurement, the value to be read is only that of the load.

1. Starred connection
2. Starred connection with star centre available
3. Chain-linked connection
4. Special chain linked connection