# Industrial Motor Selection: IEC 60034 Ratings, Starting and IE Efficiency

> How to select induction and synchronous motors around torque, duty cycle, starting method, harmonics, cooling, enclosure, altitude and the current IEC IE-efficiency classes.

- **Category:** Electric Motors & Starting
- **Author:** Voltformer Rotating Machines Engineering
- **Publication Date:** 2026-09-10
- **Reading Time:** 8 min read
- **Key Tags:** #IEC 60034-1, #IEC 60034-30-1, #IE4 / IE5, #Motor Starting, #VFD Duty
- **Canonical URL:** https://voltformer.com/articles/industrial-motors-selection-starting-current-ie-code
- **Markdown Source:** https://voltformer.com/articles/industrial-motors-selection-starting-current-ie-code.md

### 1. Rating Comes Before Efficiency

IEC 60034-1:2026 applies to rotating electrical machines and clarifies rating, performance, thermal class and converter-duty considerations. IEC 60034-30-1:2025 specifies IE efficiency classes for qualifying single-speed line-operated AC motors, with the current edition introducing IE5 limits. The IE class is only meaningful after duty, torque, environment and drive compatibility are correct.

### 2. Motor Sizing Inputs

| Input | What must be specified |
|---|---|
| **Mechanical load** | Rated torque, speed-torque curve, inertia, acceleration time and overload |
| **Duty** | S1 or another duty type, starts/hour, braking and cyclic load |
| **Environment** | Ambient, altitude, hazardous area, cooling method, IP and corrosion |
| **Supply / drive** | Voltage, frequency, voltage imbalance, harmonics, VFD dv/dt and bearing-current mitigation |

The electrical input estimate is:

$$ P_{in} = \sqrt{3} \cdot U \cdot I \cdot cos\varphi $$

and shaft output is approximately:

$$ P_{out} = \eta \cdot P_{in} $$

Use the manufacturer performance curve for starting current and torque; do not infer them from the IE class.

### 3. Starting and Protection

Across-the-line starting gives the highest inrush and voltage dip. Star-delta, soft starters and VFDs reduce the network event but change acceleration torque, harmonics and protection settings. Coordinate overload, locked-rotor, phase-loss, earth-fault, thermal model, short-circuit and restart inhibit functions with the motor and driven machine.

### 4. Procurement Data

Require rated output, pole count, efficiency at declared load, power factor, current, starting current/torque, inertia, noise, vibration, bearings, space heaters, RTDs, enclosure, paint system and test certificates. For VFD duty, specify the complete power-drive-system interface rather than treating the motor as an isolated sinusoidal-load machine.

*Reference: IEC 60034-1:2026; IEC 60034-2-1; IEC 60034-30-1:2025; IEC 61800-9-2.*

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