Winding Resistance Measurement

This page is an overview of iTIG winding resistance measurement. For details about winding resistance measurement, including types of measurements and iTIG winding resistance measurement techniques, see Winding Resistance Measurement Methods.

Why Are Winding Resistance Measurements Used?

Winding resistance measurements are used to find open windings, shorts to ground, wrong turn count, wrong wire gauge, resistive connections, round wires in hand that are not connected in a coil, some connection mistakes, the resistance balance between phases, and in some cases shorted turns.

Winding resistance is an important measurement because other tests and measurements will not find some of the problems a resistance measurement will find. Some of these are the wire gauge issues, resistive connections, and blown or disconnected magnet wires in hand.

iTIG winding resistance measurement screen
iTIG winding resistance measurement screen.

How Winding Resistance Measurement Works

Winding resistance measurements are taken while applying DC voltage and current to the device under test (DUT). The winding analyzer calculates the resistance value in µΩ (microohms) or mΩ (milliohms) according to Ohm’s law.

For a 3-phase motor, three resistance measurements are normally done between the phases, and the balance or imbalance between the three measurements is calculated and displayed along with the measurement values.

For single coils, and sometimes for motors, the measured resistance values may be compared to a defined target resistance value. In this case, the percentage difference to the target resistance value is calculated instead of calculating the balance or imbalance between the measurements.

A temperature correction factor can be automatically applied to calibrate the results to a standard temperature, which enables the results from the DUT to be more accurately tracked over time with the winding analyzer.

2-Wire versus 4-Wire Resistance Measurement

Resistance can be measured with two leads connected to a DUT. This type of resistance measurement will include the tester’s leads in the winding resistance test’s measurement. A four lead measurement is better. It eliminates the lead resistance and is typically more accurate.

All winding resistance measurements done with Electrom Instruments motor testers are done with a 4-lead system. For the iTIG model D, the leads are the high voltage output leads so the microohm winding resistance measurement can be part of an automatic sequence of motor tests including high voltage tests.

For more details about winding resistance measurements, visit Winding Resistance Measurement Methods.