Understanding Motor Starters: A Guide to Electrical Contacts and Controls

Electric motors are integral to various industrial and domestic applications, powering everything from machinery to appliances. However, these motors require a mechanism to start and stop them safely and efficiently. This is where motor starters come into play. Motor starters are electrical devices that control the operation of electric motors, protecting them from damage and ensuring optimal performance.

In its most basic form, a motor starter consists of electrical contacts and switches that enable the motor to start, stop, and protect itself from overloads and faults. Moreover, it provides the initial voltage boost required to start the motor, and once it reaches its rated speed, it transitions the motor to its running state. To better understand these complex apparatuses, we will delve into the world of motor starters, exploring their numerous types and functions.

Different Types of Electrical Contacts

At the core of a motor starter is a set of electrical contacts that are responsible for establishing and interrupting the power supply to the motor. Some of the most popular types of electrical contacts used in motor starters include electromechanical relays, thermal overload relays, and solid-state relays, all of which we will be outlining in detail below.

  • Electromechanical Relays

Commonly used in motor starters due to their reliability and simplicity, electromechanical relays use an electromagnetic coil to control the opening and closing of the contacts. When the coil is energized, it generates a magnetic field, which attracts the movable armature and closes the contacts. Conversely, when the coil is de-energized, the contacts open due to the force of a spring.

  • Thermal Overload Relays

Thermal overload relays protect the motor from excessive current by monitoring the motor's temperature. Generally, these relays contain a bimetallic strip that expands or contracts with temperature changes. For example, when the motor current exceeds the set limit, the bimetallic strip heats up and actuates the contacts, interrupting the power supply to the motor. With this in mind, thermal overload relays have become a vital part of preventing motor damage caused by overheating.

  • Solid-State Relays

Solid-state relays (SSRs) are semiconductor devices that use optocouplers or triacs to control the switching of electrical contacts. Well-known for their silent operation, fast switching speed, and long lifespan, SSRs are particularly useful in applications where noise reduction, compactness, and precision control are crucial.

Soft Starter: An Alternative Approach

In addition to a traditional motor starter, there is another type known as a soft starter. A soft starter is a device that gradually increases the voltage supplied to the motor during startup, reducing the sudden torque and current surge. This gentle ramp-up minimizes stress on the motor and connected mechanical components. For these reasons, soft starters are commonly used in applications where the starting torque needs to be limited, such as conveyor belts, pumps, and fans.


By providing the necessary control and protection mechanisms in various electrical applications, motor starters ensure reliable performance and prevent damage from overload or fault conditions. As such, it is important to understand how different types of motor starters function, that way users can select the most appropriate starter for a particular motor-driven system. More than that, with the right motor starter in place, the lifespan of electrical equipment can be expanded. If you find yourself in need of motor starters and/or their related components, check out the unrivaled inventory of available parts on Parts Needed Yesterday; we are your strategic sourcing partner when you need to fulfill inflexible operational requirements. Start sourcing today by filling out an RFQ form, and see how we can secure everything you need!


Recent Twitter Posts

Semiconductor's Certifications and Memberships

We’re Glad You Visited Us Today.

Remember Us Next Time If You are Looking for Any Types of Aviation Parts.

Request for Quote

We use cookies to ensure that we give you the amazing experience on our website. If you continue to use this site we will assume that you are happy with it.