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Motor Fuse Size Calculator helps you calculate the correct motor fuse rating using accurate formulas. Easy, fast, and reliable for all motor types.
Choosing the correct fuse for a motor is not guesswork. A motor draws high current at startup. If the fuse is too small, it will blow instantly. If the fuse is too large, the motor will not be protected. This is why a motor fuse size calculator is important.
We developed this online motor fuse size calculator to help users calculate the correct fuse rating quickly and accurately. You do not need advanced electrical knowledge. Just enter the motor details, and the calculator does the work for you.
This tool is useful for electricians, engineers, technicians, students, and DIY users.
A motor fuse size calculator is an online tool that calculates the correct fuse rating for electric motors. It uses motor power, voltage, efficiency, power factor, and motor type to determine the full load current, then applies a safety multiplier to select the correct fuse size.
This calculator follows real electrical standards used in motor protection.
Sizing a motor fuse starts with calculating the motor’s full load current. Motors do not behave like simple loads. They draw extra current during startup. Because of this, fuses must be rated higher than the running current.
The fuse size is calculated by multiplying the full load current by a suitable multiplier. This multiplier depends on the fuse type and motor starting characteristics.
The motor fuse size calculation is based on two main steps.
First, calculate the motor full load current.
For three-phase motors, the formula is written as:
FLC = Power ÷ (√3 × Voltage × Power Factor × Efficiency)
For single-phase motors, the formula is:
FLC = Power ÷ (Voltage × Power Factor × Efficiency)
Once the full load current is known, the fuse rating is calculated using:
Fuse Size = Full Load Current × Fuse Multiplier
The multiplier is usually between 1.25 and 1.75 depending on the motor and fuse type.
To calculate the motor fuse rating manually, you need the motor power, voltage, efficiency, and power factor. Convert motor power into watts if it is given in kilowatts or horsepower.
After calculating the full load current, multiply it by the recommended fuse multiplier. The final fuse value is rounded up to the nearest standard fuse size.
Our calculator performs all these steps automatically and shows the formula clearly.
Start by entering the motor power value. Select whether the power is in kilowatts or horsepower. Next, choose the motor type. Select single-phase or three-phase based on your motor.
Enter the supply voltage. Input the power factor and efficiency if available. If not, you can use common default values.
Choose the fuse multiplier. You can select a standard multiplier or enter a custom value. Click the calculate button. The calculator instantly displays the motor full load current, calculated fuse size, and the nearest standard fuse ratings.
Suppose you have a three-phase motor with a power rating of 10 horsepower. The supply voltage is 400 volts. The power factor is 0.85, and efficiency is 0.90.
First, convert horsepower to watts.
10 HP × 746 = 7460 watts
Now calculate full load current.
FLC = 7460 ÷ (1.732 × 400 × 0.85 × 0.90)
FLC ≈ 14.1 amps
Now apply a standard fuse multiplier of 1.5.
Fuse Size = 14.1 × 1.5
Fuse Size ≈ 21.15 amps
The nearest standard fuse size is 25 amps.
This is the correct fuse size for a 10 HP motor under these conditions.
The 80% rule means that a fuse should not continuously carry more than 80% of its rated current. This prevents overheating and ensures long-term reliability.
In motor applications, this rule is considered when selecting the final standard fuse size. This is another reason why fuse ratings are higher than motor running current.
The fuse size for a 10 HP motor depends on voltage, phase type, power factor, and efficiency. Most three-phase 10 HP motors require fuse sizes between 20 amps and 30 amps.
Using a motor fuse size calculator is the safest way to get the correct answer for your specific motor.
Our calculator uses real electrical formulas. It supports single-phase and three-phase motors. It accounts for power factor and efficiency. It follows NEC and IEC motor protection practices.
The results are accurate, easy to understand, and suitable for real-world applications.
Correct motor fuse sizing is critical for safety and performance. Guessing the fuse size can damage motors or cause frequent fuse failures.
Our motor fuse size calculator provides a fast, accurate, and user-friendly way to calculate motor fuse ratings. It eliminates confusion and helps users select the correct fuse every time.
Motor fuse size is calculated by multiplying the motor’s full load current by a safety multiplier, usually between 1.25 and 1.75.
No. Fuse size depends on motor power, voltage, phase type, and starting current.
No. Fuses and circuit breakers follow different sizing rules for motor protection.
Motors draw high current during startup. The fuse must allow this inrush current without blowing.
Yes. The calculator follows standard electrical engineering practices and is suitable for industrial and commercial motors.