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Use our free Motor Overload Calculator to quickly calculate overload, overload percentage, and trip settings. Step-by-step guide with examples included.
Electric motors are essential in industries and homes, but they can get damaged if they run above their rated capacity for too long. Motor overload happens when a motor draws more current than its rated full load current. This can reduce motor efficiency, increase energy costs, and shorten the motor's lifespan. To prevent this, it is important to calculate motor overload accurately.
Our Motor Overload Calculator helps you determine overload settings, overload percentage, and current overload ratio quickly and easily. This tool is developed for users to calculate motor overload online without manual errors.
Motor overload occurs when a motor carries more electrical load than it was designed for. Motors have a Full Load Current (FLC) specified on their nameplate. If the motor draws current higher than the FLC for an extended period, it heats up and risks permanent damage. Overload calculations help set overload relays and monitor motor health.
There are three primary calculations related to motor overload:
The overload relay protects the motor from prolonged overcurrent. The formula to calculate the trip setting is:
Overload Setting (A) = FLC × Setting Factor
Where FLC is the Full Load Current, and Setting Factor depends on the motor service factor:
Example:
FLC = 50 A, Service Factor = 1.15
Overload Setting = 50 × 1.25 = 62.5 A
This means the overload relay should trip at 62.5 A to protect the motor.
Overload percentage measures how much the motor is overloaded compared to its rated capacity. The formula is:
Overload % = ((Measured Current − Rated Current) / Rated Current) × 100
Example:
Rated Current = 50 A, Measured Current = 60 A
Overload % = ((60 − 50) / 50) × 100 = 20%
A motor overload percentage above 15% indicates a potential risk and requires immediate action.
Current Overload Ratio (COR) indicates the ratio of measured current to rated current.
COR = Measured Current / Rated Current
Example:
Rated Current = 50 A, Measured Current = 55 A
COR = 55 / 50 = 1.1
COR > 1.0 indicates the motor is overloaded. COR > 1.15 indicates critical overload.
This online calculator eliminates manual errors and ensures accurate overload settings.
Let’s calculate using our online tool:
Motor FLC = 40 A
Service Factor = 1.15
Measured Current = 50 A
Step 1: Overload Relay Trip Setting
Overload Setting = 40 × 1.25 = 50 A
Step 2: Overload Percentage
Overload % = ((50 − 40) / 40) × 100 = 25%
Step 3: Current Overload Ratio
COR = 50 / 40 = 1.25
Interpretation: The motor is running above safe limits and requires inspection or load adjustment.
Using a Motor Overload Calculator ensures your motors are running safely and efficiently. Accurate overload calculations prevent motor damage, reduce energy consumption, and extend the motor lifespan. Our online calculator provides instant results, step-by-step calculations, and clear status messages. It is suitable for engineers, technicians, and anyone working with electric motors.
Motor overload can be calculated using the formulas for overload relay setting, overload percentage, or current overload ratio. These formulas use the motor's full load current and measured current to determine safe operating limits.
FLC is the maximum current a motor can carry safely at its rated load. It is crucial for setting overload relays and monitoring motor performance.
A safe overload percentage is usually below 15%. Anything above 15% indicates the motor may be overloaded and at risk of damage.
Yes, most calculators allow you to enter a custom factor based on specific motor requirements or environmental conditions.
Yes, the formulas are standard and can be applied to single-phase or three-phase motors. Always use the FLC from the motor nameplate for accurate results.