Motor Fuse Size Calculator

Motor Power (kW): Voltage (V): Efficiency (%): Power Factor:

Motor Type	Horsepower (HP)	Voltage (V)	Full Load Current (A)	Recommended Fuse Size (A)
Single Phase AC	1/2	120	9.8	15
Single Phase AC	1	120	16	25
Single Phase AC	2	120	24	35
Three Phase AC	1	208	3.6	10
Three Phase AC	3	208	9.6	20
Three Phase AC	5	208	15.2	30
Three Phase AC	10	208	28	50
Three Phase AC	1	480	1.6	5
Three Phase AC	3	480	4.8	10
Three Phase AC	5	480	7.6	15
Three Phase AC	10	480	14	25
DC Motor	1	120	9.7	15
DC Motor	5	120	48	70
DC Motor	1	240	4.8	10
DC Motor	5	240	24	35

Motor Horsepower (HP)	Voltage (V)	Estimated Fuse Size (A)
1	230	10
1	460	5
2	230	15
2	460	10
3	230	20
3	460	15
5	230	30
5	460	20
7.5	230	45
7.5	460	30
10	230	60
10	460	40
15	230	90
15	460	60
20	230	120
20	460	80
25	230	150
25	460	100
30	230	175
30	460	125
40	230	225
40	460	150
50	230	300
50	460	175
60	230	350
60	460	200
75	230	450
75	460	250
100	230	600
100	460	350

Choosing the correct fuse size for your electric motors is key. It ensures safety and protection for your circuits. The motor fuse ratings match NEC rules. They’re picked based on motor power and the necessary amperes.

Almost all motor uses pair with UL Class 10 and 20 overload relays. This helps set the right motor fuse ratings.

Deciding on the right fuse size considers the service factor and if overload relays are there. For 120V motors, sizes go from 1/6 HP to 60 HP. This changes according to the voltage and other motor features.

Key Takeaways

Motor fuse ratings consider NEC rules, motor power, and size.
Fuse sizes are from the motor’s full load current. Most use UL Class 10 and 20 overload relays.
Guidance is available for fuse size with motor protection tables.
For motors without overload relays, fuse sizes range from 0.08A to 1.08A based on their current.
Fuse clip ratings change by voltage, motor power, and overload relay use.

Understanding Motor Fuse Size Requirements

Electrical Characteristics of Motors

Think of electrical flow in a wire like water moving in a pipe. A small pipe, with lots of water but little pressure loss, can represent this. But if the pipe is long, the water loses pressure due to contact with the pipe walls. This shows the need for a bigger pipe to keep water pressure stable.

This example is similar to electrical flow. A wire needs more space (conductor size) as the distance increases to prevent pressure (voltage) drop. This concept helps us understand how wire size relates to the length and electric current it carries.

Characteristic	Data Point
Fuse Ratings for Motor Horsepower and Full Load Amps	The tables provide fuse ratings for different motor horsepower and Full Load Amps (FLA) based on motor characteristics.
Motor Running Protection	Fuses can be selected for motor running protection based on motor horsepower or actual Full Load Currents (FLA).
Fuse Rating Alignment with NEC	Fuse ratings align with NEC requirements for Motor Branch circuit and Short-Circuit Protection.
Overload Relay Coverage	Over 90% of motor applications are covered by UL Class 10 and 20 overload relays.
Motor Service Factor Impact	Motor Service Factor impacts fuse selection for motor running protection.
Fuse Ampere Ratings for Motor HP Ranges	Specific fuse ampere ratings are recommended for various motor HP ranges for different types of motors and protection requirements.
Fuse Clip Ratings for 460V 3-Phase Motors	For 460 Volt 3-Phase Motors, fuse clip ratings vary depending on whether overload relays are present or not.
Fuse Clip Ratings for 575V 3-Phase Motors	For 575 Volt 3-Phase Motors, fuse clip ratings differ for motors with and without overload relays.
Fuse Clip Ratings for 120V 1-Phase and 230V 1-Phase Motors	For 120 Volt 1-Phase and 230 Volt 1-Phase Motors, specific fuse clip ratings are provided for different motor HP ranges.
Fuse Reducers	Fuse reducers may be required for certain motor categories.
Switch or Fuse Clip Ratings	Switch or fuse clip ratings are provided based on Service Factor and Temperature Rise considerations for varied motor configurations.

Understanding Motor Fuse Size Requirements

Factors Affecting Fuse Size Selection

Protecting motors is key, and choosing the right fuse size matters a lot. A few big factors help decide the correct fuse size for a motor. Normally, you’d use a time-delay fuse that’s rated 175% of the motor’s usual amp usage. If there’s a circuit breaker, it should be 250%. This makes sure the motor is safe from too much power or shorts, as the NEC or CEC demands.

Also, the wire connected to a motor needs to handle 25% more power than the motor uses at its max. Usually, you can see the needed power on the motor’s tag. Sometimes, the wire needs to be bigger if the power has to travel a long way. This is to stop the voltage from dropping too much. The right wire size keeps the power flow steady and avoids problems.

For motors, using time delay fuses is a good idea. They guard against overloads and short circuits better than regular fuses. When selecting the fuse’s power, it’s usually set at 125% to 150% of what the motor normally uses. This way, it won’t turn off for minor issues but still protects well. For very efficient motors, the required fuse power might be a bit higher, like 125% to 150%. This is due to their specific features.

To keep your motor and your whole electrical system safe and working right, keep these points in mind. Choosing the right fuse size makes sure your motor is safe and your system is reliable.

Determining Motor Fuse Size

Choosing the right fuse is crucial. It must meet both safety standards and electrical code needs. Look at the motor’s FLA on its nameplate. Find the right fuse size by matching this FLA to the chart. A fuse with the correct amp rating is your best bet for safety.

For safety, use a time-delay fuse. It should be 175% of the motor’s FLA, or 250% if you use a breaker. The wire to the motor should handle 125% of the motor’s load. This ensures it won’t overheat. Using certain fuse types ensures most motor needs are met.

For different horsepowers and motor types, there are specific amp ratings for fuses. Motors with a service factor of 1.15 or more have specific fuse sizes for safe use.

Consider using Class RK5 and POWR-PRO® Class RK1 fuses based on the motor’s specifics. These fuses, when properly chosen, meet the NEC rules for protection.

Operating Voltage

The chart shows a big range of operating voltages for various motors. It covers 460V 3-phase motors (480V circuit), 575V 3-phase motors (600V circuit), and more. Each type has its own voltages and needs different fuse ratings.

It’s vital to pick the right fuse ratings for these different motor operation voltages. This ensures the motors are safe and work well with the system’s other electrical parts.

The Motor Protection Tables list what fuse ampere ratings are best for each motor voltage. They help people choose the right fuses for their specific motor needs.

Motor Voltage	Recommended Primary Fuses	Recommended Secondary Fuses
460V 3-phase (480V circuit)	LESRK, ECSR, JDL, LCL+	LENRK, ECNR, NCLR, JDL, LCU
575V 3-phase (600V circuit)	LESRK, ECSR, JDL, LCL+	LENRK, ECNR, NCLR, JDL, LCU
120V 1-phase (120V circuit)	LESRK, ECSR, JDL, LCL+	LENRK, ECNR, NCLR, JDL, LCU
230V 1-phase (240V circuit)	LESRK, ECSR, JDL, LCL+	LENRK, ECNR, NCLR, JDL, LCU
200V 3-phase (208V circuit)	LESRK, ECSR, JDL, LCL+	LENRK, ECNR, NCLR, JDL, LCU
230V 3-phase (240V circuit)	LESRK, ECSR, JDL, LCL+	LENRK, ECNR, NCLR, JDL, LCU

This table is really helpful for choosing the right fuses. It’s based on the voltage your motor works on. It makes picking the correct fuses much easier.

Power Rating

The Motor Protection Tables provide info on motor HP and FLA. This info is taken from NEC® Tables 430.248 to 430.250. It talks about AC motors with normal torque characteristics. If a motor has special traits, its fuse ratings might differ from the standard ones.

Single-phase motors usually have fuse protection with UL Classes RK5, RK1, J, and CC. The fuse ampere ratings depend on the motor’s HP and the current it uses when fully loaded. Time delay fuses are a good choice for these motors. They provide better protection against overloads. The recommended fuse ampere ratings for these motors range from 15A to 225A. This can vary based on the motor and the fuse type.

Three-phase motors running on 208V might need fuse ratings as low as 2.4A for 0.5HP motors. For 40HP motors, the fuse rating can be as high as 114A. At 460V, fuse ratings for these motors can vary from 1.1A for 0.5HP to 361A for 300HP. When running on 575V, fuse ratings start at 0.9A for 0.5HP up to 302A for 250HP.

Selecting Fuse Size

Choosing the right fuse size for motor protection is key for top performance and safety. Guidelines point out that time-delay RK1 and RK5 fuses picked correctly also align with NEC® needs for Motor Branch circuit and Short-Circuit Protection. When choosing Class RK5 Fuses (FLNR_ID / FLSR_ID / IDSR SerieS), or POWR-PRO® Class RK1 Fuses (LLNRK / LLSRK / LLSRK_ID Series), consider the motor’s Full Load Amps.

Manufacturers like Edison offer detailed suggestions to help with fuse selection. For primary fuses, they propose using LESRK, ECSR, JDL, and LCL+. For secondary fuses, they recommend LENRK, ECNR, NCLR, JDL, and LCU. These include fuse classes and symbols like Class L, Class RK1, Class RK5, Class J, Class CC, and Class T. They are approved by U.L. and are a great guide for protecting motors.

Factors to keep in mind include motor service factor, temperature rise limits, and voltage when picking the right fuse ampere ratings. This is needed for different motor horsepower and full load amp ranges. By using these detailed guidelines, your motor will have the right fuse size, meeting NEC® needs, and work reliably.

FAQ

What is the relationship between electrical flow in a wire and water flow in a pipe?

Think of electrical flow in a wire like water in a pipe. Imagine a short pipe with plenty of water at one end, and a faucet and gauge at the other. When you open the faucet, the gauge shows little drop.

But, make the pipe long. Now, open the faucet and watch a significant pressure drop in the gauge. This drop happens because water rubs against the pipe’s walls, causing friction.

To fix this, make the pipe larger. Then, even when the faucet is on, the pressure drop is small. Current in a wire works the same way. It faces resistance, just like water in a narrow pipe.

What are the NEC® requirements for Motor Branch Circuit and Short-Circuit Protection?

The NEC® needs fuses chosen based on certain guidelines for Motor Branch Circuit and Short-Circuit Protection. When picking fuses for motors, find the motor’s full load current on the nameplate. Then match this current with the right fuse ampere rating.

What types of motors are covered in the Motor Protection Tables?

The Motor Protection Tables include different types of motors. These are 460V 3-phase motors, 575V 3-phase motors, 120V 1-phase motors, and more. It lists motors up to 230V and 200V.

What factors may require variations in fuse ratings for motors with special characteristics?

Motors with unique features might need different fuse ratings than standard motors. This allows for better protection and safety.

What are the recommended fuse ratings for motor protection?

For motor protection, use a time-delay fuse that’s 175% of the motor’s normal amperage. If you have a circuit breaker, this goes up to 250%. Also, the wire to the motor should handle 25% more amps than the motor demands.

What are the key considerations for selecting fuse size based on motor full load amps?

Choosing time-delay fuses like RK1 or RK5 includes important considerations. Following these choices also meets the NEC® standards for Motor Branch Circuit and Short-Circuit Protection. When selecting fuses based on full load amps, use Class RK5 or POWR-PRO® RK1 Fuses.

Motor Fuse Size Calculator