Calculator
Example data table
| Motor | Power | Voltage | Efficiency | Power factor | Current density | Parallel strands | Typical note |
|---|---|---|---|---|---|---|---|
| Three phase star | 1.5 kW | 415 V | 88% | 0.82 | 4.5 A/mm² | 1 | Common small industrial motor |
| Single phase | 0.75 kW | 230 V | 78% | 0.72 | 4 A/mm² | 2 | Use separate start winding checks |
| Three phase delta | 5 HP | 230 V | 86% | 0.84 | 3.8 A/mm² | 2 | Check phase current carefully |
Formula used
Three phase line current: I = P / (√3 × V × η × PF)
Single phase line current: I = P / (V × η × PF)
DC current: I = P / (V × η)
Delta phase current: Iphase = Iline / √3
Star phase current: Iphase = Iline
Required copper area: A = (Iphase / J) × (1 + margin)
Wire diameter: d = √(4A / π)
Resistance at temperature: R = ρ20 × [1 + α(T - 20)] × L / A
Slot fill: Fill = insulated conductor area / slot area × 100
How to use this calculator
Enter the motor type, rated power, supply voltage, efficiency, and power factor. Select star or delta for a three phase motor. Add your target current density, strands, slot area, and fill limit. Press calculate. Review current, copper area, wire size, resistance, copper loss, and slot fill result.
Motor winding wire size guide
Motor winding design starts with current. The wire must carry load current without excessive heat. A small wire raises resistance. It also increases copper loss. A large wire may not fit inside the slot. This calculator balances those limits.
Why current density matters
Current density shows amperes carried by each square millimeter of copper. Low values run cooler. High values save space but create more heat. Many small motors use higher values. Larger motors usually need lower values. Cooling, duty cycle, insulation class, and ventilation change the safe value.
How the calculator works
The tool first converts rated power to watts. It then estimates line current from voltage, efficiency, and power factor. For a three phase motor, it also adjusts phase current for star or delta connection. The phase current is divided by target current density. That gives the required copper area.
The selected parallel strands divide the copper area. This helps when one large conductor is hard to bend. The calculator then finds a standard metric wire diameter. It also compares the need with a nearby AWG size. The result includes bare area, recommended diameter, current density, resistance, and copper loss.
Slot fill check
Slot space is limited. A wire may look correct electrically but still fail physically. The slot fill estimate uses insulated diameter, conductors per slot, and slot area. It compares the used space with your allowed fill percentage. A high fill warning means you should reduce diameter, increase slots, use parallel strands, or review the winding layout.
Practical winding notes
Use measured slot data when possible. Old motors may have worn or varnished slots. Count turns carefully before removing coils. Record coil pitch, lead positions, and connection type. Rewinding needs the same magnetic pattern. Wire size alone cannot restore a motor if turns, pitch, or insulation are wrong.
Safety and accuracy
This calculator gives an engineering estimate. It does not replace motor design standards. Always check insulation class, temperature rise, starting current, and local electrical rules. Final selection should be tested with no load and load current. Stop testing if the winding heats quickly or draws abnormal current.
FAQs
What is motor winding wire size?
It is the copper conductor diameter or area used in a motor coil. It must carry phase current safely while fitting inside the stator or rotor slot.
Which current should I use?
Use phase current for winding design. In star connection, phase current equals line current. In delta connection, phase current is line current divided by square root of three.
What current density is suitable?
Common estimates range from 3 to 6 A/mm². Lower values suit cooler and heavier duty motors. Higher values need better cooling and careful testing.
Why use parallel strands?
Parallel strands make winding easier when one large wire is stiff. They also help fit conductors into slots. The total copper area must still meet the current need.
Does insulation affect slot fill?
Yes. Bare copper size is not the final physical size. Enamel, varnish, liners, and slot wedges all reduce usable space inside the slot.
Can this replace original winding data?
No. Original turns, pitch, poles, groups, and connection pattern remain critical. This calculator only estimates wire size from electrical and slot inputs.
Why is copper loss shown?
Copper loss estimates winding heat from current and resistance. High copper loss may indicate small wire, long turns, high temperature, or poor design margin.
What if slot fill is too high?
Try more parallel strands, a revised slot plan, lower current density, or verified original data. Do not force coils into slots, because insulation may fail.