The Ultimate Buyer's Guide for Purchasing Electric Motor Big

Here are questions we might ask to help you identify the electric motor you’re looking for.

Want more information on Electric Motor Big? Feel free to contact us.

Purchasing electric motors can often be a complex process. The sheer number of specifications and details to consider can be overwhelming.

If you have an existing motor that needs replacing, the easiest solution is to provide the vendor with the motor’s identification plate that is typically attached to the side.

The identification plate, seen here for a TechTop TA2BTAI aluminium motor, provides critical specifications, such as:

• Power/current requirement (AC or DC)
• Power type (single phase or three phase)
• Material (cast iron vs cast aluminium)
• Speed rating
• Power rating

Some details, like mounting options (foot vs flange, or both), might be added after manufacturing based on customer orders. Thus, the identification plate may not provide all necessary information.

In this article, we’ll guide you through the considerations when selecting an electric motor, focusing on:

 

Average Lifespan of an Electric Motor

Research indicates that certain types of motors have an average lifespan exceeding 12 years when operated under normal conditions. However, this is heavily influenced by factors such as:

• Type of motor
• Kilowatt / Horsepower rating relative to load
• Usage
• Operating conditions
• Maintenance
• Voltage imbalances and fluctuations

For detailed information, check out our additional articles on:

 

Is it an AC or DC Motor?

The primary distinction between these motors lies in the type of current that powers them.

Alternating current (AC) motors:

• Are recognized for their high efficiency
• Operate quietly and offer flexibility
• Are available in both single-phase and three-phase configurations
• Convert energy from magnetic fields (from the coils)

In contrast, direct current (DC) motors:

• Are noted for their output range
• Can run at variable speeds
• Are available only in single-phase configuration
• Draw energy from constant voltage external power sources like batteries

We offer a wide selection of AC induction motors from TechTop Australia. Please refer to their latest catalogue.

 

Is it a Single-phase or Three-phase AC Motor?

Typically, single-phase motors:

• Run on a single-phase power source
• Are simpler and easier to manufacture and maintain
• Are commonly employed in light household and consumer applications with lower power needs (e.g., conveyors, fan pumps, fans, washing machines, pumps)

Conversely, three-phase motors:

• Operate on a three-phase power source
• Are more complex and harder to produce and maintain
• Are commonly found in high-demand commercial and industrial applications requiring greater power (e.g., driving lathes, cranes, agitators, crushers)

Additionally, there are dual voltage motors that:

• Are designed to work with two specified voltages (typically 240 V and 480 V), wired differently to maintain output
• Are popular in rural areas lacking a 240V supply, allowing connection to one of the three phases from the mains to operate at 480V

 

Do You Prefer Cast Aluminium or Cast Iron?

Cast aluminium electric motors:

• Boast a more appealing aesthetic
• Exhibit superior heat dissipation
• Resist corrosion more effectively
• Are lighter and easier to install

On the other hand, cast iron electric motors:

• Feature a sturdier casing that withstands more wear
• Provide greater mechanical strength
• Are known for their longevity
• Are heavier and more complex to install

Consider how similar motors in specifications can differ significantly in weight—e.g., a cast aluminium motor versus a cast iron motor.

 

What’s the Speed Rating?

A motor's speed is a function of its frequency rating and the number of poles it has, which is rated in revolutions per minute (RPM).

Typically, more poles (or pole pairs) result in slower motor speed paired with increased torque.

For instance, a motor with 2 poles will have a speed twice that of a motor with 4 poles—all the way down to an 8-pole motor which runs at a quarter of the speed.

 

To determine rated RPM, you can use the formula:

[120 x Frequency] &# ÷ # of poles

 

For example, using the Australian standard of 50 Hz, the RPM for different pole configurations can be computed as follows:

2-pole: [120 x 50 Hz] ÷ 2 = 3,000 RPM

4-pole: [120 x 50 Hz] ÷ 4 = 1,500 RPM

8-pole: [120 x 50 Hz] ÷ 8 = 750 RPM

Additionally, understanding synchronous and operating speeds is crucial:

• Synchronous speed: The motor's speed with no load (calculated above with the standard frequency).
• Operating speed: The motor's speed when under load.

*Analogously, synchronous speed is akin to brake horsepower (engine power measured at the flywheel), while operating speed relates to wheel horsepower (engine power at the wheels, accounting for inertia, power transmission inefficiencies, and vehicle weight).

Key Point: If utilizing a three-phase motor at various speeds, a variable frequency drive (often known as a variable speed drive) will be necessary. This device manages the frequency of electricity powering the motor, affecting speed alongside the number of poles.

Alternatively, modifying speed may necessitate a gearbox. It is advised that you maintain speeds within +/− 20% of the rated speed to avoid damage. For instance, a motor rated for 3,000 rpm should not exceed approximately 3,600 rpm or drop below around 2,400 rpm.

Speed rating and power rating are critical factors to consider when selecting a motor.

 

What’s the Power Rating?

The power rating of a motor indicates its output capacity or the amount of work it can accomplish over time. Generally, smaller electric motors provide this rating in kilowatts or horsepower.

*Here's a kilowatt-to-horsepower conversion tool for convenience.

This is often confused with torque, which signifies the actual rotary force produced by the motor that turns the shaft, measured in Newton meters (Nm).

To highlight, aside from speed rating, power rating weighs heavily in determining which electric motor suits your needs.

 

What is the Shaft Diameter and Length?

Ensuring the appropriate fit and alignment of the shaft with the component it will drive is crucial for the overall function, safe operation, and lifespan of the electric motor.

Generally:

• Short but thick shafts can produce more torque but rotate at slower speeds.
• Long but thin shafts can rotate faster but yield less torque.

 

What’s the Mounting Position?

The mounting position indicates how an electric motor can be installed.

Common mounting options include:

• Foot mount
• Flange mount (often called face mount)
• Multi-mount (both foot and flange mounts)

On TechTop motors that we offer, the foot mount can be repositioned sideways, allowing it to be installed with the terminal box to the side instead of the top, per the provided image.

According to the TechTop Installation and Maintenance Manual, motors should ideally be secured to a sturdy base to mitigate excessive vibration. Shims can be employed if the foundation is uneven and should be located next to and between the motor's mounting bolts.

*Refer to mounts and size chart (page 28 of the TechTop catalogue) Critical Note: Installation should only be performed by trained professionals. Improper installation or use can lead to severe injury or even fatalities. Always consult the installation manual.

 

Understand the Manufacturer Nomenclature

It’s essential to note that different manufacturers might employ varied nomenclature for their motors.

The following is an example based on TechTop motors:

*Exemplified below is the part number logic for TechTop TM Series of aluminium single-phase motors

Key considerations for purchasing TechTop motors include:

• Capacitor Start (CS) / Capacitor Run (CR): In simple terms, this indicates that the motor uses two capacitors in parallel, each tailored to control torque during starting and operation. These motors are sometimes referred to as two-value capacitor motors for this reason. Informally, they are often called Cap Start/Cap Run. Such motors are typically employed where the motor is frequently activated and deactivated (e.g., lathes).
• Permanent Split Capacitor (PSC): This configuration uses one capacitor for motor operation in both starting and running phases. Typically, you will find these in applications where the motor runs continuously for extended periods, such as with a fan that powers on at the beginning of a shift and stays on for eight hours. These motors are widely used in fan and pump applications.

Key Point: Select the appropriate motor for your application, as using the wrong motor type can lead to rapid failure.

 

Additional Key Considerations

• Most motors are made to be unidirectional; they can only rotate in one direction: clockwise (CW) or counterclockwise (CCW), based on wiring.
• Some motors are bi-directional (able to rotate both directions), and some even feature self-reversing capabilities.
• Certain motors are specifically designed for hazardous conditions where explosion risks are high. One notable example is TechTop's TCD YBX3 series of flameproof motors (Ex d), certified for Zone 1 hazardous areas and compliant with IEC and IEC standards. Popular designs also include non-sparking motors (Ex nA) and dust ignition protected motors (Ex tD).
• Some motors come equipped with brakes that hold loads if the shaft comes to a stop.

Final Tips

Make sure:

• The motor is safeguarded against dust and liquid ingress during installation and operation.

This concerns the ingress protection (IP) ratings of the motor, especially important in scenarios like marine and mining applications. You can sometimes upgrade a motor's IP rating when necessary. Most of the TechTop motors we sell have an IP55 rating for limited dust ingress and low-pressure water jets from all directions.
Learn more about electric motor IP ratings.

• Ensure all electrical connections are solid and uninterrupted, with circuit breakers, fuses, and protective devices compatible and rated to function adequately with the motor, particularly during startup and full load.
• Double-check that starters and overload protections have appropriate trip and load ratings.
• Remove any loose items on or near the motor or within the housing that could obstruct movement.

Do not:

• Hinder the cooling system or the airflow meant to keep the motor operating at safe temperatures.
• Couple the motor with the wrong pulley, fan, and/or gearbox.

For more details, please refer to our motor selection guide.

 

Note on Safe Use of Belt-Driven Systems

(For more on this topic, see our content library's sub-index of articles about belt-driven systems and electric motors.)