Free Engineering Tool
Motor Winding Resistance Calculator
Correct winding resistance measurements for temperature difference. Supports copper and aluminum windings. Includes 3-phase unbalance check — >2% between phases indicates a problem.
Results
Temperature Correction Formula
The resistance of a conductor changes linearly with temperature. The standard correction formula is:
- R₁ — measured resistance at temperature T₁
- R₂ — corrected resistance at target temperature T₂
- k — material constant: 234.5 for copper, 225.0 for aluminum
Material Properties
| Material | α at 20°C (1/°C) | k constant | ρ at 20°C (Ω·m) |
|---|---|---|---|
| Copper (annealed) | 0.00393 | 234.5 | 1.724 × 10⁻⁸ |
| Aluminum | 0.00403 | 225.0 | 2.650 × 10⁻⁸ |
Phase Resistance Unbalance
For 3-phase motors, compare resistance between phases:
- < 1% — Excellent, normal condition
- 1–2% — Acceptable, monitor
- > 2% — Problem: possible shorted turns, poor connections, or winding degradation
- > 5% — Severe: motor should be removed from service for repair
⚠️ Important: All three phase readings must be taken at the same temperature. Allow the motor to reach thermal equilibrium (at least 30 minutes idle for large motors) before measuring.
Tip: For motors measured hot after running, you can back-calculate the winding temperature: T_hot = (R_hot/R_cold) × (k + T_cold) − k. This helps assess insulation thermal class loading.
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Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
