6 Considerations for Choosing the Best-Fit Starter Motor Control Technology

For different type of electrical motors and there are different type of motor starting technologies available. Adding more to that depending on the application, power availability and feature you require you may need more than combination of one technology.  

What is a Motor Starter and How does it Work?

A motor starter is an electrical device that is used to start, stop and protect an electric motor from damage and to control the starting process of the motor. 

Motor Starter

Typical motors have requirement for high inrush current while starting and tend to overload when connected equipment is over working. That’s why motor starters have heavy duty motor rated switches or contactors which are capable of handling 6 times of the current during starting and also have a set of thermal or electronic overload devices which will cause the switch or contactor to trip during overload conditions. Motor starters also have over current protection devices like fuses or breakers in them to prevent any shorts or damages to the circuit and connected motor.

Before you choose a motor starting technology for your motor consider following

  • Do you need a speed control?
  • Do you need to limit the inrush current?
  • Do you want remote starting, stopping or controlling features?
  • Do you have AC and DC power available to run the motor?
  • Do you have 1 phase or 3 phase power available?
  • What type of application?

There are several types of motor starters, including manual starters, magnetic starters, and solid-state starters. Each type of starter works in a slightly different than each other but the essentially does the same role of starting and protecting the motor.

Types of Motor Stater

There are three main type of motor starters.

  • Manual Motor starter


Manual Motor Starter
Manual Motor Starter

Manual motor starter is combination of a heavy-duty motor rated switch with a set of bimetallic thermal overload, this motor starter can be only turned on or off manually being in front of the starter but this will automatically trip in case of overload situation and you have to manually reset it.

  • Magnetic motor starter
Magnetic Motor Starter
Magnetic Motor Starter

Magnetic motor starter is combination of a magnetic contactor and set of bimetallic or electronic overload device, this motor starter can be turned on or off manually being in front of the starter or remotely. This technology can also be integrated with other devices like sensors, float switches or PLCs to start or stop automatically

  • Solid State Motor Starter
Solid State Motor starter
Solid State Motor Starter

Solid state motor starter has all the feature of magnetic motor starter and additionally this can limit the inrush current of the motor, speed control of the motor and provide you monitoring data like current, voltage and torque.

Also Read : Tips to Update your Motor Starter

Factors to Consider for Selecting Motor Starter

1. Contactor Size & Line Power

The size of a contactor and the line power are related because the contactor must be sized appropriately to handle the line power of the motor it is controlling.

Line power refers to the electrical power that is supplied to the motor, typically in terms of voltage and current. The size of the contactor must be capable of handling the line power of the motor, meaning that it must be able to carry the current required by the motor without overheating or otherwise being damaged.

There are several factors that influence the size of the contactor, including the type of motor, application of motor, the voltage and current requirements, the duty cycle of the motor, Contactor are marked with voltage and motor horsepower they can run. In general, larger motors will require larger contactors, while smaller motors can be controlled by smaller contactors.

2. Overload Relay Range

Overload Relay

An overload relay is a protection device used in motor power circuit to prevent motors from overloading or overheating. The overload relay range refers to the range of current values within which the relay will activate to protect the motor.

The overload relay range is set to match the full load current of the motor. The full load current is the amount of current required to operate the motor at its rated output power. The overload relay range should be set such that it will activate if the current exceeds the full load current of the motor by a certain percentage, typically between 10% to 25% of the motor rated current.

Some overload has fixed range so it is important to choose the right overload relay range for a specific motor to ensure that it will be protected against overloading or overheating. Other overload relays have an adjustable range to set. It is very important to set the range by figuring out the full load current of the specific motor, it duty cycle and application.

3. AC Coil Control Power

AC Coil Control

The AC coil control power of a contactor refers to the power required to energize the coil of the contactor to close the power and auxiliary contacts and energize the motor. The AC coil control power can be supplied by the same AC source as the motor, or it can be supplied by a separate lower AC or DC power source. 120VAC or 230V and 24VDC are most common coil control voltages in the industry.

Always make sure coil control power must be sufficient to energize the coil and close the contacts properly. Coil power consumptions is always listed on the contactor name plate.

4. Enclosure Cover Buttons

Enclosure Cover Button

This is referring to switches or pilot lights installed on the door of the control panel enclosure

There are few things to keep in mind when designing or installing these items on the enclosure door. Enclosures have an environmental rating which tell thee are indoor, outdoors or dust proof. The operators must have the same rating of the enclosure or above. 

Some enclosures could be really tall, consider installing all the operable switches within human reach, A safe distance will be 6 feet when measuring of the working platform where a work will stand and operate these.

5. Full Torque at Zero Speed

“Full torque at zero speed” refers to the capability of an electric motor to produce its maximum torque output when it is not rotating or at a standstill. This is an important characteristic for applications where quick and powerful starting is required, such as in electric vehicles, drill presses, conveyors or some other industrial machinery. Motors with this capability are commonly known as “torque motors” or “zero speed torque motors”.

Variable Frequency Drives can be used to achieve full torque at zero speeds by adjusting the voltage to provide the correct level of power to the motor.

The frequency setting should be set to match the optimal operating frequency of the motor. High frequency will increase the torque, but also the heat generated by the motor.

Also Read: Useful Tips for Extending the Lifespan of Starter Motor

6. Cost, Size, and Thermal Considerations

The cost, size, and thermal considerations of a Variable Frequency Drive are important factors to consider when selecting a VFD for a specific application.

Cost: Mostly the cost of the VFD depends on the input voltage, size, features and brand. Typically larger and more advanced VFDs will be more expensive, while smaller and basic models will be less expensive. It’s important to balance the cost with the specific requirements and features needed for the application.

Size: The size of the VFD will depend on the motor power and the specific features required. Larger VFDs will be able to handle run larger motors and provide more advanced features, while smaller VFDs will be more compact and suitable for smaller motors.

Thermal considerations: The thermal performance of the VFD is a critical factor to consider. The VFD must be able to dissipate heat generated by the motor and the VFD itself, to avoid overheating and potential damage. The thermal performance will depend on the design and cooling system of the VFD, ambient temperature and the specific requirements of the application.