Motor Overload Setting Calculator (KW/HP to Relay Setting)
A Motor Overload Setting Calculator helps electricians, panel builders, and maintenance engineers quickly convert motor power into the correct overload relay setting. Instead of manually checking motor nameplates or doing long calculations, this tool gives you the full load current (FLA) and the recommended overload relay range instantly.
Correct overload relay settings are important for protecting motors from overheating, phase failure, and prolonged overcurrent. If the overload setting is too low, nuisance tripping can occur. If it is too high, the motor may overheat before protection operates.
Using a Motor Overload Setting Calculator reduces errors and improves motor protection accuracy, especially in industrial control panels, MCC panels, and motor starter circuits.
Motor Overload Setting Calculator
Motor Overload Setting Calculator
Estimate Full Load Amps and a safe thermal overload relay range for AC induction motors, based on nameplate rating, supply voltage, efficiency and power factor.
3-Phase | kW / HP | IEC & NEC style marginsMotor Data
Results
| Min Setting | Max Setting | Typical Setting |
|---|---|---|
| — | — | — |
How to Use This Calculator
- Select the rating unit for your motor (kW or HP) and enter the nameplate rating.
- Choose the supply voltage from the dropdown, or select “Manual entry” for non-standard voltages.
- Adjust efficiency and power factor if known from the motor nameplate; otherwise keep the pre-filled defaults.
- Pick a service condition that reflects the motor’s duty, starting frequency and ambient conditions.
- Click “Calculate Overload Setting” to view the estimated FLA and the recommended overload relay range.
- Use the Typical Setting as your starting point, and fine-tune during commissioning based on actual measured current.
Technical Notes
The overload relay protects the motor winding insulation from sustained thermal damage caused by prolonged overcurrent, locked rotor conditions, or single-phasing. Its setting must be closely matched to the motor’s actual full load current rather than the supply breaker or contactor rating.
- Efficiency and power factor account for real electrical losses and the reactive component of current draw, so the calculated FLA reflects actual line current rather than only the mechanical output rating.
- Standard duty band (100% – 125%) reflects common industrial practice for continuous-duty motors operating in a controlled ambient environment.
- Higher ambient / frequent start conditions increase heating, so the acceptable band is shifted slightly to allow margin without nuisance tripping.
- Light duty / conservative selection tightens the band for motors on sensitive or intermittently loaded applications where earlier tripping is preferred.
- Where the nameplate FLA is available, always prefer it over a calculated value — this tool is intended for sizing estimates, pre-commissioning checks, or situations where the nameplate is missing or unreadable.
- Three-phase motors are assumed for this calculation. Single-phase or DC motors require a different current relationship and are outside the scope of this tool.
How to Use This Calculator
Using the Motor Overload Setting Calculator is simple and takes only a few seconds.
Follow these steps:
- Select the motor rating unit (kW or HP).
- Enter the motor power.
- Select the operating voltage.
- Enter motor efficiency if available.
- Enter power factor if known.
- Click calculate.
- Read the Full Load Amps (FLA).
- Check the recommended overload relay setting.
- Review the minimum and maximum safe setting range.
If efficiency and power factor are not entered, the calculator uses default values:
| Parameter | Default Value |
| Efficiency | 0.88 |
| Power Factor | 0.80 |
This makes the Motor Overload Setting Calculator practical for quick field calculations when motor data is not available.
Find the exact setting using our Motor Overload Setting Table which includes 3 Phase Chart & Complete Guide
How Motor Overload Setting Is Calculated
The overload relay setting is usually based on the motor’s full load current. The basic logic is simple.
First, calculate the motor full load current.
For three-phase motors:
FLA = kW × 1000 ÷ (√3 × Voltage × Efficiency × Power Factor)
For horsepower:
kW = HP × 0.746
After calculating FLA, the overload relay setting is normally adjusted between 100% and 125% of FLA depending on motor type and operating conditions.
Typical formula:
Overload Setting = FLA × Overload Margin
Example:
| Parameter | Value |
| Motor Power | 15 kW |
| Voltage | 415V |
| Efficiency | 0.88 |
| Power Factor | 0.80 |
| Calculated FLA | 29.6A |
| Overload at 110% | 32.5A |
The Motor Overload Setting Calculator automates this process and removes manual errors.
For the full calculation method, refer to the main hub guide on motor overload setting calculations.
Motor kW/HP to FLA Reference Chart
This chart helps users quickly check standard motor currents without entering values into the calculator.
Motor FLA Reference at 415V
| Motor kW | Motor HP | Approx FLA (A) |
| 0.5 | 0.67 | 1.2 |
| 0.75 | 1 | 1.8 |
| 1.5 | 2 | 3.1 |
| 2.2 | 3 | 4.5 |
| 3.7 | 5 | 7.4 |
| 5.5 | 7.5 | 11.2 |
| 7.5 | 10 | 15.3 |
| 11 | 15 | 22.4 |
| 15 | 20 | 30.6 |
| 18.5 | 25 | 37.8 |
| 22 | 30 | 44.9 |
| 30 | 40 | 61.2 |
| 37 | 50 | 75.5 |
| 45 | 60 | 91.8 |
| 55 | 75 | 112.2 |
| 75 | 100 | 153 |
| 90 | 120 | 183.6 |
| 110 | 150 | 224.4 |
| 132 | 175 | 269.3 |
| 160 | 215 | 326.4 |
| 200 | 268 | 408 |
Voltage Impact on FLA
Higher voltage reduces motor current for the same power.
| Motor Size | 230V | 400V | 415V | 690V |
| 7.5 kW | 27.6A | 15.9A | 15.3A | 9.2A |
| 15 kW | 55.2A | 31.8A | 30.6A | 18.4A |
| 30 kW | 110.4A | 63.5A | 61.2A | 36.8A |
This is why voltage selection matters in the Motor Overload Setting Calculator.
Overload Relay Setting Range (Min/Max Guidance)
A single overload value is not always ideal. Motors work under different load conditions, and this changes how the relay should be set.
That is why the Motor Overload Setting Calculator shows a range.
Standard Overload Setting Guide
| Condition | Recommended Setting |
| Light Duty Motor | 100% to 105% FLA |
| Normal Duty Motor | 105% to 110% FLA |
| Heavy Duty Motor | 110% to 125% FLA |
Why the Range Matters
Service Factor
Motors with a service factor above 1.0 can safely handle more load for short periods. This may justify a higher overload setting.
Duty Cycle
Frequent starts or stop-start operations create temporary high current. A low setting may cause unwanted trips.
Ambient Temperature
High temperatures increase motor winding heat. In hot environments, careful overload adjustment is critical.
Load Type
Conveyors, compressors, and crushers usually need a slightly higher overload margin because of higher starting and running torque.
Practical Example
| Motor FLA | Min Setting | Typical Setting | Max Setting |
| 20A | 20A | 22A | 25A |
| 40A | 40A | 44A | 50A |
| 100A | 100A | 110A | 125A |
This makes the Motor Overload Setting Calculator useful for both quick design work and real-world troubleshooting.
Frequently Asked Questions
How do you calculate motor overload setting from kW or HP?
First convert motor power into full load current using voltage, efficiency, and power factor. Then multiply the FLA by the overload margin, usually between 100% and 125%. A Motor Overload Setting Calculator performs this instantly.
What is the standard overload relay setting range for a motor?
Most motors are set between 100% and 125% of full load current. Normal applications often use 105% to 110%.
Does overload setting change with voltage?
Yes. Lower voltage means higher current for the same motor power. Since overload settings depend on current, voltage directly affects the final relay setting.
What is the difference between FLA and overload relay setting?
FLA is the actual current the motor draws at full rated load. The overload relay setting is the protective current limit set slightly above FLA to avoid nuisance trips while protecting the motor.
Choosing the correct overload setting improves motor life, prevents winding damage, and reduces downtime. Whether you are designing a motor control center, selecting thermal overload relays, or troubleshooting motor trips, this calculator gives quick and practical results for every motor size.
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Motor Overload Setting Calculator (KW/HP to Relay Setting) : Electrical Engineering Hub
Free motor overload setting calculator — enter motor kW/HP and voltage to get FLA, recommended relay setting, and min/max range instantly.
Price Currency: USD
Operating System: All
Application Category: UtilitiesApplication
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