A motor nameplate is one of the most useful pieces of information when buying or replacing a variable speed drive. A clear photo can prevent the most common VSD selection mistakes.
1. Motor kW
The kW value is the motor's rated mechanical output and is the usual starting point for drive selection. It is not enough by itself because motors with the same kW can have different rated currents.
2. Rated Voltage and Phase
Confirm the motor's rated voltage and whether it is a three-phase motor. The available supply, the VSD input class and the motor winding voltage all need to be compatible.
3. Full-Load Current
Look for the rated current in amps. This is one of the most important final checks. The VSD must have a continuous output-current rating suitable for the motor and the intended duty, with any required derating taken into account.
4. Frequency and Speed
Most South African industrial motors are based around a 50Hz supply, but the nameplate should be checked. Rated RPM helps identify the motor's base speed and gives context for the number of poles and expected slip.
5. Delta and Star Connection
Many motor plates show two voltages together with delta and star symbols. Those markings indicate how the windings are intended to be connected at the stated voltages. Do not change the motor connection or select a different voltage-class drive without confirming the motor's permitted winding voltage.
6. Duty, Insulation and Enclosure
Duty rating, insulation class, IP rating and ambient conditions can affect whether a motor and VSD are suitable for an application, especially at low speed, high ambient temperature, high altitude or inside a hot enclosure.
Replacing an Existing VSD?
Send both the motor nameplate and the old VSD nameplate. Also explain the application. A drive that worked on a pump may have been selected differently from one used on a heavily loaded conveyor or mixer.
A Practical Planning Checklist
- Clear motor nameplate photo
- Old VSD nameplate if replacing a drive
- Motor kW
- Motor voltage
- Motor full-load current
- Frequency and rated speed
- Delta/star voltage information
- Supply voltage and phase
- Application and load type
- Required speed range and control method
- Site and enclosure conditions
Technical Note
This guide is general selection guidance. Final drive sizing, motor connection, protection, cable sizing and installation must be verified against the exact equipment documentation and applicable electrical requirements.
Related catalogue examples: Variable Speed Drives. For an equipment enquiry, contact Softcore Group Industrial Solutions at info@softcoregroup.co.za.