When performing winding resistance checks, what is a typical trend to expect with healthy windings?

• A. Phase resistances should be similar and within tolerance; large variations indicate issues.
• B. All phase resistances should be zero.
• C. Resistance should increase dramatically with load.
• D. Resistance should be identical to the impedance of the supply.

Answer: (A)

When checking winding resistance, you’re looking at the DC resistance of each winding. In a healthy set, the phase-to-phase resistances should be very similar and fall within the specified tolerance. This happens because each winding is designed with the same wire gauge, the same number of turns, and the same path length, so their resistance values come out nearly the same. If you see large differences between phases, it points to faults such as an open winding, a shorted turn, damaged insulation, or loose connections.

A few related ideas help solidify the concept: measure with the winding de-energized, at a temperature close to the measurement reference, and compare each winding to its peers or to the nameplate value. Temperature affects resistance, so you may need corrections if readings are taken at different temperatures. Also, the winding’s resistance is a property of the winding itself and does not suddenly become zero or match the supply’s impedance. Under AC operation, the overall impedance includes reactance, but the DC resistance of healthy windings remains a small, consistent value and does not “increase dramatically with load.”