HomeElectricalUnderstanding Motor Nameplate Specifications: Voltage, Power, Current, and More

# Understanding Motor Nameplate Specifications: Voltage, Power, Current, and More

Motor nameplate specifications provide crucial information about a motor’s performance, including its voltage, power, current, and operating conditions. Understanding these specifications is essential for ensuring proper installation, operation, and maintenance of motors. This article delves into the key aspects of motor nameplate specifications data, explaining how to interpret voltage ratings, power output, current requirements, and other important details. Whether you’re an engineer, technician, or DIY enthusiast, mastering these elements will help you optimize motor performance and troubleshoot issues effectively.

## What Can You Understand from the Motor Nameplate Voltage?

Three-phase motor nameplates typically show something like “230Δ/400Y (13.6/7.8A).” 230Δ means 230 volts in delta configuration and 13.6 amps of current. 400Y means 400 volts in star configuration and 7.8 amps of current.

To explain better, let’s use an example. Suppose we have a 4 kW three-phase induction motor with a nameplate reading 230Δ/400Y (13.6/7.8A).

This means the motor can operate at two different voltages: one for delta and one for star.

For a three-phase induction motor, power comes through three wires. If I get 230 volts across two wires, then my line voltage will be 230 volts.

If I want to get 4 kW output at this voltage, the motor must be connected in delta configuration, and it will draw 13.6 amps of current.

Similarly, if the line voltage is 400 volts, to achieve 4 kW power, I need to connect the motor in star configuration, which will draw 7.8 amps of current.

If the line voltage is 230 volts, the motor can be run in star configuration, but it will only provide one-third of the full output. Motors that provide full output in delta configuration can be run with a star-delta starter.

However, if a motor’s nameplate specifies that it provides full output at 400 volts in star configuration, the motor cannot be connected in delta configuration. Connecting the motor in delta would make it operate as a 12 kW motor (4*3=12 kW).

Since the voltage is fixed, to produce this amount of power, the line current will need to be three times the rated star line current, i.e., 7.8*3=23.4 amps. This will result in a phase current of 23.4/√3 = 13.52 amps, which is nearly double. This could cause the coils to overheat.

## What Can You Understand from the Motor Nameplate Power?

The kilowatts written on the motor indicate the mechanical output of the motor, which is typically expressed in horsepower. If we calculate the current based on the motor’s nameplate kilowatts, it will not always match the current specified on the motor.

For example: For single-phase: (KW*1000)/V*cosθ; For three-phase: (KW*1000)/√3 * V*cosθ

If you calculate the power using the motor’s nameplate kilowatts, it will not match. The reason is that kilowatts represent the mechanical output of the motor. There is some loss in converting electrical power to mechanical power, as noted on the motor.

The total power a motor consumes is its input power. To determine the motor’s total power, first calculate the input power, then divide the output power by the motor’s efficiency. The efficiency value is usually indicated on the motor, e.g., EFF: 85% or NOM. EFF:85%. This means the motor will provide 85% of the input power as output.

## What Can You Understand from the Motor Nameplate Current?

Sometimes the motor nameplate specifications shows: FLA – 17A. FLA stands for Full Load Amperes, which is 17 amps.

When a motor runs without a load, it draws what is known as no-load current, which is much lower. This current is generally used to rotate the motor’s rotor. In this condition, the motor is not performing any work.

For instance, if a motor is lifting a heavy load from the ground up to the fifth floor, the gravitational force will pull the load downward. When the load is coupled to the motor’s rotor, the gravitational force will try to pull the rotor downwards.

At that moment, the motor will start drawing more current than the no-load current. This current generates torque and converts electrical power to mechanical power.

The more resistance there is to the rotor’s rotation, the more current the motor will draw and the harder it will work. When the motor provides its mechanical output, the current it draws is known as full load amperes, which depends on the supply voltage.

When the voltage is supplied as per the nameplate, it will be equal across all three phases, and the motor will draw the amperes specified on its nameplate.

The size of the motor’s cable and the settings of the overload relay are determined based on this current value.

## What Does It Mean if the Motor Nameplate Specifies the Phase?

This indicates the number of phases the motor will operate with. The motor nameplate specifications will specify whether it is a single-phase or three-phase motor.

## What Can You Understand from the RPM on the Motor Nameplate?

RPM stands for Revolutions Per Minute, which indicates the number of rotations per minute. This is given on all motor nameplates. The RPM value is based on the motor’s slip and represents the maximum speed the motor can achieve while delivering full load mechanical power.

The motor might show: F/L RPM:2800 or 2800r/min

## What Does It Mean If the Motor Nameplate Shows ENCL-ODP/TEFC or Enclosure?

Sometimes, the motor nameplate specifications shows ENCL-ODP/TEFC. ENCL stands for Enclosure, which means something enclosed on all sides. Here, the enclosure refers to the motor’s entire body, which houses all its parts.

Induction motors have two types of enclosures: one is ODP – Open Drip Proof and the other is TEFC – Totally Enclosed Fan Cooled. The enclosure type indicates how safe the motor is from the surroundings and how it will be cooled.

ODP – Open Drip Proof: In this case, air can directly enter the motor, allowing the coils to cool easily and the motor to be protected from vertical water drips if the angle of water droplets is between 0-15 degrees. This motor is not waterproof.

TEFC – Totally Enclosed Fan Cooled: Air cannot directly enter this motor, and it has a fan on the opposite side of the shaft that rotates at the same speed as the motor. This motor is protected from water and air ingress.

## What Does INS-B or INS-CL-F on the Motor Nameplate Indicate About Insulation?

The motor nameplate specifications might show INS-B or INS-CL-F. INS stands for Insulation. We know that the coils of the motor are insulated to prevent short circuits.

Insulation has a relationship with temperature. Higher temperatures can weaken the insulation, and if it continues to increase, the insulation will eventually break down, leading to a short circuit.

The motor’s temperature depends on the surrounding temperature and the core and copper losses of the motor. The sum of these temperatures is called the operating temperature. The insulation class indicates this temperature rating.

Insulation classes are denoted by: A, B, F, H, etc. The later the letter in the alphabet, the better the insulation. For example, F grade insulation is better than A and B but worse than H.

When purchasing a motor, it’s advisable to choose one with higher insulation as these motors are more durable.

## What Does “Design: B” or “NEMA Design: A” on the Motor Nameplate Mean?

The motor nameplate specifications might show “Design: B” or “NEMA Design: A,” which indicates the design code. Induction motors handle various types of loads. Some motors are used for blowing air, while others are used as cranes. This represents the motor’s centrifugal or axial load. Different loads have different torque requirements.

The design code indicates the starting torque of the motor. Based on this, induction motors are divided into four types: A, B, C, D.

If a motor used in one place is replaced with another motor of the same rating but with a different design code, various issues may arise.

## What Does SF-1.15 on the motor nameplate specifications Mean?

SF – Service Factor: SF-1.15 indicates that the motor can deliver 15% more output than its nameplate kilowatt rating for a short period, provided the voltage remains within tolerance during that time.

Motors often need to handle temporary high loads. The motor is designed based on this requirement. It is not advisable to operate a motor continuously at its service factor rating because it can affect the motor’s torque, temperature, and efficiency.

The service factor is above 1 to account for various factors such as temperature, altitude, and line voltage imbalance. To mitigate these effects, the service factor is set above 1.

Open drip-proof motors typically have a service factor of 1.15, while totally enclosed fan-cooled motors have a service factor of 1.0. For motors without a specified service factor, assume it is 1.

## What Does the Motor Code “CODE-E” or “KVA CODE-D” Mean?

Motor Code: Induction motors draw more current at startup than their normal operating current, usually 5-7 times higher. While we know this, we do not know the exact amount of current. However, this current value is written on the motor as a code.

The motor may have “CODE-E” or “KVA CODE-D” written on it. Let’s see how to determine the starting current value from this code.

Use the following formula:

For single-phase motors: (code * horsepower * 1000) / supply voltage

For three-phase motors: (code * horsepower * 577) / supply voltage

Note: Do not convert horsepower to watts by multiplying by 746, as shown in the chart. Use the two values in the middle column to determine the minimum and maximum starting current. The applied voltage of the motor affects this.

## What Does “DUTY-CONT” on the Motor Nameplate Mean?

DUTY-CONT: Duty Continuous means that this motor is suitable for continuous operation. Most industrial motors have this feature. However, for motors not designed for continuous use, the duration in minutes is specified, indicating how long it can run continuously. Such motors are used in cranes.

## What Does “AMB-40°C” or Ambient Temperature on the Motor Nameplate Mean?

AMB stands for Ambient, which refers to the surrounding environment. It indicates the maximum ambient temperature at which the motor can safely operate.

We know that motors generate a lot of heat due to core and copper losses. This heat disperses into the surrounding air.

If the ambient air temperature around the motor is very high, the air cannot absorb much heat, causing the motor to run hotter, which affects the insulation life of the motor.

To get good service from the motor over time, this aspect must be considered. The motor nameplate specifications indicates this as “AMB-40°C.”

## What Does “FRAM-143T” on the Motor Nameplate Mean?

Sometimes, the motor nameplate specifications is labeled as “FRAM-143T.” The first two digits indicate the distance from the mounting surface to the centerline of the motor shaft. To find this distance, divide the two numbers by 4, and the result will be in inches, i.e., 14/4=3.5 inches.

The third digit (3) represents the distance between the bolt holes for mounting, but this number does not indicate a specific distance. Generally, a higher number means a longer motor.

For motors of 1 horsepower or less, the frame size is indicated by two letters, such as FRAM-58. Here, the two numbers indicate the distance from the mounting surface to the centerline of the motor shaft. To find this distance, divide the number by 16, i.e., 56/16=3.5 inches.

## What Does Altitude on the Motor Nameplate Indicate?

Altitude refers to the height of a location above sea level. Although this is not always specified, it can significantly affect performance. If the motor’s nameplate specifies the maximum altitude for full load operation, the motor should be operated at reduced load at higher altitudes to prevent excessive heat buildup, which the less dense air at higher altitudes cannot dissipate.

Alternatively, the motor might be able to run at full load at higher altitudes with a special cooling system that ensures the heat generated is not excessive compared to normal operating conditions.

## What Does the Power Factor on the Motor Nameplate Mean?

The power factor provided on the motor nameplate specifications usually represents the full load power factor. We have discussed power factors in detail before.

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Md Nazmul Islam
An expert in Electrical & Electronics engineering, I combine my academic background with hands-on experience to craft insightful content. Collaborating with the Voltage Lab team and skilled educators, I’m passionate about sharing research-backed knowledge to empower others in the field.

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