3-Phase Asynchronous Electric Motors

3-phase asynchronous electric motors are industrial motors supplied from a 400 V three-phase network, with their speed set by the number of poles. HEM Motor offers this series from 0.25 to 355 kW at 3000, 1500 and 1000 rpm (2, 4 and 6 poles): aluminium frame 0.25–11 kW, cast iron frame 0.55–355 kW. Protection class IP55, insulation class F, frequency 50 Hz.

The tables below are taken from the product cards of the models in our shop: for every power and speed you will find the model code, IEC frame, nameplate (rated) speed, rated current at 400 V and rated torque. Click a model code to open the product page for price and ordering.

General Technical Specifications

Power range

0.25–355 kW (1/3–485 HP)

Phases and frequency

3-phase, 50 Hz

Synchronous speed

3000 rpm (2 poles), 1500 rpm (4 poles), 1000 rpm (6 poles)

Voltage

0.25–3 kW: 230/400 V (Δ/Y) · 4–355 kW: 400/690 V (Δ/Y)

Frame

Aluminium 0.25–11 kW · Cast iron 0.55–355 kW

IEC frame size

63 – 400

Protection class

IP55

Insulation class

F

Mounting

B3 foot; B5, B14, B34, B35 flange and vertical V1/V3/V5/V6/V15 depending on frame — flange size confirmed with the order

Certification

CE

Model, Frame and Nameplate Speed by Power and Speed

Each cell shows the model code (IEC frame) and the rated speed on the nameplate. Models from 0.55 to 11 kW are available with both aluminium and cast iron frames; their electrical values are identical.

Once you have found the right model, you can see the current price on its product page and order directly from the online store.

Rated Current at 400 V and Rated Torque

Values are the ratings on the product cards; actual current depends on load, supply voltage and connection. Cables, fuses and overload relays are sized from the current on the motor nameplate. Values marked “—” are confirmed with the quotation.

Voltage and Connection: 230/400 V vs 400/690 V

Models up to 3 kW have 230/400 V windings and are connected in star (Y) on a 400 V three-phase network. Models of 4 kW and above have 400/690 V windings and are connected in delta (Δ) on a 400 V network. That is why motors of 4 kW and above are suitable for star-delta starting, while direct-on-line starting is common for small ratings.

Always connect the motor according to the voltage on its nameplate. When replacing an existing motor, compare the voltage and connection data on the old nameplate with the new one; electrical connection must be made by a qualified electrician with the power switched off.

How Speed, Slip and Torque Are Related

Synchronous speed is calculated from the supply frequency and the number of poles: speed = 120 × frequency / number of poles. At 50 Hz, 2 poles give 3000, 4 poles 1500 and 6 poles 1000 rpm. The rotor of an asynchronous motor turns slightly slower than this; the difference is called slip, which is why the nameplate shows, for example, 1460 rpm rather than 1500.

Slip decreases as power increases: in the table the 0.25 kW 6-pole model is rated at 855 rpm, while the 250 kW 6-pole model is rated at 990 rpm. At the same power, torque rises as speed falls; at 7.5 kW the 4-pole 132M-4 delivers 49.1 Nm and the 2-pole 132S2-2 delivers 24.4 Nm. The speed and torque the machine needs determine the number of poles.

Frame, Mounting and Operating Conditions

The aluminium frame (0.25–11 kW) is light and widely used in general applications such as fans, pumps and conveyors. The cast iron frame (0.55–355 kW) is preferred under vibration, dust or heavy-industry conditions. For the same model code, the electrical values of both frames are identical.

The series is suitable for speed control with a frequency converter (inverter); for long periods at low speed with full torque an external fan may be needed, and if the cable between drive and motor is long a dv/dt or sine filter is considered. These conditions should be stated with the order.

Where to Continue

• 1500 rpm electric motors
• 3000 rpm electric motors
• 1000 rpm electric motors
• Aluminium frame electric motors
• Cast iron frame electric motors
• Compact electric motors
• Three-phase electric motors model map

For a 220 V single-phase supply, single-phase electric motors are a separate series (0.18–5.5 kW) and are not included in the tables on this page.

Information Needed for Ordering or Replacement

• Power (kW) and speed (rpm) — ideally a photo of the existing motor’s nameplate
• Supply voltage and connection (230/400 V or 400/690 V)
• Mounting (B3, B5, B14, B35, vertical) and flange size
• Frame preference (aluminium or cast iron)
• Application, duty and environment (dust, humidity, temperature), and inverter use if any

With this information you can choose a suitable model from the models in our store, or send a nameplate photo via the WhatsApp line on our contact page to ask for a model.

Frequently Asked Questions

Why does the nameplate say 1460 rpm instead of 1500?

The rotor of an asynchronous motor turns slightly behind the rotating magnetic field (slip). 1500 rpm is the synchronous speed; the nameplate shows the rated speed at full load.

On a 400 V network, is the motor connected in star or delta?

A motor rated 230/400 V (up to 3 kW in the HEM series) is connected in star; a motor rated 400/690 V (4 kW and above) is connected in delta.

Can I replace a 4-pole motor with a 2-pole motor?

The machine would run about twice as fast and, at the same power, torque would be halved. This is not recommended without recalculating the pump, fan or gearbox side.

Is there a difference between the aluminium and cast iron versions of the same model?

In HEM product data the electrical values (speed, current, torque) of the same model code are identical for both frames; the difference lies in the frame material and robustness.