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A 7.5 kW (10 HP) three-phase motor is one of the most requested ratings for conveyors, pumps, fans, mixers and workshop machinery. When buying, the power is usually already known; the real questions are how the motor will sit on the machine and what environment it will run in. In this article we use HEM Motor's six 7.5 kW models on sale to explain the order in which you should settle the frame material, the IEC frame size and the mounting arrangement.
Six options at 7.5 kW: three speeds, two frame materials
At HEM Motor, 7.5 kW is offered at 1,000, 1,500 and 3,000 rpm synchronous speed, with both an aluminium and a cast iron frame. That gives six models for the same power. The model code changes with speed, not with frame material: the aluminium and the cast iron 1,500 rpm models both carry the code 132M-4. Their electrical values are also identical. All models have IP55 protection, class F insulation and a 400/690 V (Δ/Y), 50 Hz supply.
| Model code | Synchronous / rated speed | IEC frame | Rated current (400 V) | Rated torque | Product page |
|---|---|---|---|---|---|
| 160M-6 | 1,000 / 970 rpm | 160M | 15.4 A | 73.8 Nm | Aluminium · Cast iron |
| 132M-4 | 1,500 / 1,460 rpm | 132M | 14.3 A | 49.1 Nm | Aluminium · Cast iron |
| 132S2-2 | 3,000 / 2,930 rpm | 132S | 13.7 A | 24.4 Nm | Aluminium · Cast iron |
The rated speed in the table is the speed under load that you will see on the motor nameplate. A model searched for as a "1,500 rpm motor" shows 1,460 rpm on its nameplate; this difference is the natural slip of an induction motor, not a defect.
Why does the frame grow when speed drops at the same power?
The most striking point in the table is that the 1,000 rpm model uses a 160M frame, while the 1,500 and 3,000 rpm models use a 132 frame. The reason is torque. Power depends on the product of torque and speed; if the speed is halved, almost twice the torque must be transmitted to the shaft to deliver the same power. At 7.5 kW, rated torque is 24.4 Nm on the 3,000 rpm model and rises to 73.8 Nm on the 1,000 rpm model. Higher torque means a larger rotor, more iron and copper, and therefore a larger frame.
By standard, the number in the IEC frame code describes the shaft height above the foot base; the letter (S, M, L) indicates the frame length and the foot hole spacing class. That is why 132S and 132M share the same shaft height but do not have their foot holes in the same place. 160M is both a higher and a larger frame.
When replacing an existing motor
- Compare the frame code on the old motor's nameplate (e.g. 132M) with that of the new model. If the code is the same, the baseframe, base and coupling alignment will most likely stay unchanged.
- Do not change the speed by looking at power alone: putting a 1,000 rpm model in place of a 1,500 rpm motor both changes the machine's speed and, because of the larger frame, requires adapting the base.
- If the frame code on the nameplate cannot be read, measure the foot hole spacing and the shaft height on site and compare them with the technical drawing; do not order on guesswork.
Aluminium or cast iron?
Both frames have the same protection and insulation class; the choice depends on where the motor will run and on the structure of the machine. The list below is a decision framework, not a strict rule.
- Aluminium frame: Lighter, easier to carry and install. Preferred for fans, pumps, packaging machines and mobile equipment running in enclosed, relatively clean environments. The low weight also helps in applications where the motor hangs on the machine by its flange.
- Cast iron frame: A more rigid structure that is more resistant to impact. It stands out in environments with dust, vibration and mechanical shock; in stone, mining, woodworking and heavy-industry machinery, as well as on damp and demanding sites.
- What they share: Both options have IP55 protection, class F insulation and the same electrical values. The frame material does not change the motor's power or speed.
If there are conditions beyond IP55, such as continuous water jets, chemical vapour or extreme temperature, state them separately in the order; such conditions may fall outside the scope of a standard motor.
