PangPang ToolsAC motor synchronous speed calculator: Checking pole count and frequency — Worked Scenario
How do you check checking pole count and frequency without overlooking a default value or an assumption? Follow the input and result from AC motor synchronous speed calculator, then review what can change the output before using it.
Tool walkthrough based on an illustrative example; this page is still awaiting an independent content review. Do not treat it as official guidance or a verified regulatory result.
Check the worked example in AC motor synchronous speed calculator
What this scenario actually checks
The rotating magnetic field of an AC motor has a synchronous speed set by the electrical frequency and the number of magnetic poles. The formula is rpm = 120 × frequency (Hz) ÷ poles. This tool also displays electrical cycles per minute and the number of pole pairs. It estimates field speed, not the actual loaded shaft rpm of an induction motor, which runs slightly slower because of slip.
This walkthrough focuses on checking pole count and frequency. It follows the published tool inputs, not a new formula or an automatically verified legal, financial, medical or engineering determination.
Start by preparing the right inputs
Enter the electrical supply or variable-frequency-drive output frequency in hertz (Hz). Enter the motor's total pole count as an even integer, such as 2, 4, 6 or 8. Do not enter pole pairs in place of poles.
Before copying the example, confirm that each entered unit, date, dimension and default matches your real task. Changing only a visible number without revisiting its assumptions can change what the answer means.
- Enter the electrical supply or variable-frequency-drive output frequency in hertz (Hz).
- Enter the motor's total pole count as an even integer, such as 2, 4, 6 or 8. Do not enter pole pairs in place of poles.
- Calculate synchronous speed = 120 × Hz ÷ poles. The tool also shows frequency × 60 cycles/minute and poles ÷ 2 pole pairs.
Worked example with the calculator
Use the following input values: 60 Hz; 4 poles.
The example output is Synchronous speed 1,800 rpm; 3,600 cycles/min; 2 pole pairs. 120 × 60 ÷ 4 = 1,800 rpm. A four-pole induction motor generally runs below this under load.
For comparison, the same tool also documents these inputs: 50 Hz; 6 poles. Its result is Synchronous speed 1,000 rpm; 3,000 cycles/min; 3 pole pairs. 120 × 50 ÷ 6 = 1,000 rpm. Changing pole count or frequency changes the rotating-field speed.
What can change the answer
Calculate synchronous speed = 120 × Hz ÷ poles. The tool also shows frequency × 60 cycles/minute and poles ÷ 2 pole pairs. Compare the result with the motor nameplate. Induction-motor slip, drive control, mechanical loading and motor type affect actual shaft speed.
Why is the nameplate rpm lower than this result? For an induction motor, slip is required to produce torque; the rotor commonly turns below the rotating field's synchronous speed.
What frequency should I enter for a VFD-fed motor? Use the drive's actual output electrical frequency at the operating point, not necessarily the fixed utility mains frequency.
Before using the result for a real decision
For checking pole count and frequency, check the original measurements and input units, and save the assumptions alongside any number you share.
Where legal rules, official allowances, equipment ratings or contractual conditions matter, consult their current authoritative documents. An illustrative estimate is not a substitute for that verification.
- Reproduce the example before changing inputs
- Check all units and assumptions, including any default values
- Verify official or manufacturer-specific requirements outside the calculator
Related tools
Use the tools to verify the steps against your own files or text.