Reading a motor nameplate
What the data on an induction motor nameplate mean — voltage and connection, current, power, speed, power factor, frequency, efficiency class — and which values a drive needs.
Typical nameplate data
| Field | Example | Meaning |
|---|---|---|
| Voltage / connection | 400 V Δ / 690 V Y | Supply voltage for delta / star connection |
| Current | 28.5 A / 16.5 A | Rated current for each connection |
| Power | 15 kW | Mechanical output power at the shaft |
| Speed | 1460 rpm | Rated speed at rated load (slip below 1500 rpm synchronous) |
| Frequency | 50 Hz | Supply frequency for the data above |
| cos φ | 0.85 | Power factor at rated load |
| Efficiency / class | 92 % / IE3 | Efficiency and class per IEC 60034-30-1 |
| Duty | S1 | Continuous duty |
| Insulation class | F | Winding temperature limit |
| IP | IP55 | Protection against dust and water |
Useful relations
- Synchronous speed:
n_s = 60 · f / p(p = pole pairs). 1460 rpm at 50 Hz → 4 poles (2 pole pairs), slip ≈ 2.7 %. - Electrical input:
P_el = √3 · U · I · cos φ— at 400 V, 28.5 A, 0.85: ≈ 16.8 kW; output 15 kW → efficiency ≈ 89 % (nameplate values are rounded). - Torque:
M = 9550 · P[kW] / n[rpm]→ 15 kW at 1460 rpm ≈ 98 Nm.
Star or delta
The winding is designed for one voltage per phase. A motor marked 230 V Δ / 400 V Y is connected in star on a 400 V network; a motor marked 400 V Δ / 690 V Y runs in delta on 400 V (and is suitable for star-delta starting). Wrong connection → overcurrent or weak torque.
What the drive needs
VFDs ask for rated voltage, current, power, frequency, speed and cos φ (sometimes efficiency) for the connection actually used, then measure the motor in the identification run. Wrong nameplate data is one of the most common causes of overcurrent trips and poor speed control.
Connections
Open in Knowledge Graph →Loading the map…
Sources
Updated 2026-10-02