Electric Motor Rewinding Calculation: Formulas, SWG Chart & Wire Weight
Rewinding an electric motor requires high accuracy. A tiny error in coil turn calculations or wire gauge selection can lead to excessive heating, efficiency drop, or early insulation failure. Whether you are servicing a 3-phase industrial induction motor or a single-phase household unit, having correct rewinding formulas is crucial.
In this technical guide, we break down standard electric motor rewinding calculation step-by-step, provide a clear wire size comparison chart (SWG vs. AWG), and offer an interactive copper wire weight calculator for your convenience.
Interactive Copper Winding Weight Calculator
Calculate the estimated copper wire weight required for your stator winding quickly:
Key Step 1: Determining the Number of Turns per Coil
To calculate turns per coil correctly, engineers use the main voltage, magnetic flux, and core dimensions. The basic electromotive force (EMF) equation for stator coils is written as follows:
Stator Winding Formula:
E = 4.44 × f × Φ × N × Kw
- E: Supply Phase Voltage (Volts)
- f: Supply Power Frequency (50 Hz or 60 Hz)
- Φ (Phi): Magnetic Flux per Pole (Webers)
- N: Number of Turns per Phase
- Kw: Winding Factor (typically between 0.92 and 0.96)
To find the total turns required per slot, rearrange the formula to solve for N based on your core area (Length × Diameter of stator core).
Key Step 2: Wire Gauge (SWG / AWG) Selection
Selecting the right wire gauge ensures that the current density remains safe (typically 4 to 6 Amperes per square millimeter). Using thinner wire increases internal resistance and thermal overload risks.
Standard Wire Gauge (SWG) vs American Wire Gauge (AWG) Chart
Use this reference table to compare standard enamelled copper wire sizes for electric motor repairs:
| SWG Size | AWG Equivalent | Diameter (mm) | Cross-Section (mm²) | Max Current Rating (A) |
|---|---|---|---|---|
| 18 SWG | 16 AWG | 1.22 mm | 1.167 mm² | 5.8 A |
| 20 SWG | 19 AWG | 0.91 mm | 0.656 mm² | 3.3 A |
| 22 SWG | 21 AWG | 0.71 mm | 0.397 mm² | 2.0 A |
| 24 SWG | 23 AWG | 0.56 mm | 0.245 mm² | 1.2 A |
Key Step 3: Insulation Material & Pitch Selection
Modern rewinding relies heavily on quality slot insulation. Using Class H or Class F Nomex/Mylar paper provides long-lasting dielectric protection against high heat build-up. Always preserve the original coil pitch pattern during teardown to avoid altering speed and torque characteristics.