Electric Motors
Motor Slip Calculator
Motor Slip is a worksheet for comparing one electrical condition at a time, with the result tied to its inputs.
Calculate Motor slip
The defaults only show how Motor Slip works; replace them with values for the actual equipment or period.
Inputs to verify for Motor Slip
Collect Synchronous speed, and Measured speed from the same operating case before reading motor slip.
- Synchronous speed
- Enter synchronous speed in rpm. Default shown: 1500 rpm.
- Measured speed
- Enter measured speed in rpm. Default shown: 1440 rpm.
When synchronous speed is uncertain, run a low and high case instead of hiding that uncertainty in one entry.
The Motor Poles Frequency page can be useful as a follow-up, but only after the present inputs have been checked.
How motor slip is calculated
Only the entries shown on Motor Slip feed motor slip. If another correction factor matters, keep it in the notes or make a separate run.
The formula uses Synchronous speed, and Measured speed to produce Motor slip. Unit mistakes usually show up as an answer that is off by a factor of 10, 100, or 1,000.
The Motor slip value and any supporting metrics belong to this same Motor Slip case, not to a nearby run with different inputs.
Read the Motor Slip equation from the units on this page. A familiar symbol can shift meaning between DC, AC, energy, component, or billing work.
Applying motor slip carefully
If motor slip is near a limit, preserve the calculated value from Motor Slip and apply required margin after the calculation.
Keep Motor Slip tied to the motor nameplate, supply system, duty cycle, and starting condition.
Records for measured speed
Record the motor nameplate, supply voltage, enclosure, duty, and whether Motor Slip describes running or starting.
If a later Motor Slip run changes only synchronous speed, label it as sensitivity work. Several changed conditions deserve a new baseline.
Detail checks for motor slip
Motor Slip should distinguish starting, running, and overloaded motor conditions. A nameplate value is not always the same as a measured load value.
When motor slip becomes an input to another worksheet, copy the value only after the units and source condition have been verified.
Using Motor Slip carefully
Can this replace a design review?
No. Treat Motor Slip as arithmetic support; ratings, safety factors, code requirements, and manufacturer limits still need review.
Why might a real measurement disagree?
A field reading for Motor Slip can include losses, tolerance, temperature effects, waveform distortion, or instrument limits that the worksheet does not model.
What does a Check inputs message usually mean?
On Motor Slip, Check inputs usually means a required entry is missing, outside its allowed range, or creating an undefined operation.
When should this be run again?
Run a new Motor Slip case when the source condition changes, such as voltage, load, rate schedule, temperature, component, connection, or period.