Electric motor starters are important components of countless applications that power our daily lives, particularly in commercial and industrial settings. They are designed to safely manage fundamental processes in the use of electric motors.
What exactly are they and why are they necessary? In this article, we will consider their inner workings and the important functions they play in residential, commercial, and industrial appliances.
What is an Electric Motor Starter?
An electric motor starter is a device used to control a motor’s access to power while providing overcurrent protection. Its key functions include:
- Starting and Stopping a Motor Safely
Using a specialized relay system, starters offer a controlled way to start and stop motors. When starting, they gradually increase voltage to the motor, accelerating it to the right speed without the mechanical stress that would result from an abrupt start. They similarly make the stopping process gradual instead of abrupt, minimizing wear and tear and prolonging its lifespan.
To understand why this is necessary, consider how induction motors work. Initially, an induction motor requires a lot of power to start up, much higher than what it requires when running. This initial power, known as inrush current, can be five to eight times what it needs to run smoothly.
Inrush current can overheat the motor’s windings, damaging or destroying the motor. The sudden demand for power can also cause a temporary dip in overall electric supply, damaging other devices connected to the same power line.
Motor starters manage this by limiting the inrush current and maintaining it at a safe level. As a motor gradually speeds up and gets to a stable operating speed, the starter gradually allows more power to flow until it reaches normal operating conditions.
- Safeguarding the Motor Against an Overcurrent or Low Voltage
Whenever there is excessive current in the motor’s circuit resulting in overheating or an extreme current surge, a thermal or magnetic relay system breaks the circuit. Moreover, the system has a voltage sensor that detects drops in supply and automatically cuts power off when it detects voltage levels that can cause the motor to stall or damage it.
- Reversing a Motor’s Direction
In applications that require bidirectional movement (such as certain types of conveyors, lifts, and hoists), starters can reverse the phase sequence of power supply. By changing the order of phases going into the motor, they reverse the direction of the magnetic field and by extension, the motor’s rotation.
Components: Understanding Contactors and Overload Relays
To understand how a starter functions, let us take a closer look at its main components:
- Overload Relays
Overload relays play a protective role, preventing motors from taking in too much current and overheating in the process. It is responsible for monitoring the current to the motor, tripping whenever current levels go above or below preset limits.
There are two main types of overload relays, thermal and magnetic. Thermal overload relays use a bimetallic strip that bends gradually in response to increasing current and breaks the circuit. Since its response is gradual, it has a time delay that allows the circuit to withstand harmless overloads for brief periods without having to break the cycle.
A magnetic overload relay on the other hand is designed to respond immediately to a sudden overload. Whenever current surges to excessive levels, it generates an electromagnetic force that trips the circuit.
- Contactors
Contactors refer to electric switches that make or break contact terminals to switch power on and off to the motor’s circuit. A contactor has main contacts responsible for handling the load current, as well as auxiliary contacts that control tasks. It also has a magnetic coil that creates a magnetic field that opens and closes the contacts.
For safety purposes, it has an arc protection mechanism designed to extinguish any arcs inadvertently produced when breaking high current.
The contactor has the role of starting and stopping the motor by making or breaking its circuit connection. Operators can control this function using start and stop buttons that automatically engage and disengage the aforementioned magnetic coil.
Types of Motor Starters
Though there are numerous types of starters, they are broadly categorized into two distinct types: manual and magnetic.
- Manual Starters
These devices use a manual switch to start and stop the motor and are therefore relatively easy to operate, even without much experience. To protect the motor from excessive current, they have built-in overload protection. A good example of this type of starter is the Direct Online Starter (DOL).
Their main downside is that they require physical presence to operate. Additionally, they do not have low voltage protection and in case of power failure, they restart automatically when power resumes. They are therefore not considered ideal for large motors or for motors located in areas that are hard to reach.
- Magnetic Starters
These are a more complex type of starter that uses electromagnets to control operations. They are ideal for high-power motors and provide remote operation capabilities.
Magnetic starter use a combination of electromagnets, contactors, and overload relays to control power flow. The contactor acts like a switch controlled electromagnetically instead of physically, as is the case with the manual starters. Popular types of magnetic starters include Full Voltage Reversing (FVR), Full Voltage Non-Reversing (FVNR), and Reduced Voltage starters.
In addition to their key advantage of remote operation, these starters also offer better protection against overloads and short circuits. They are also more versatile than their manual counterparts and are used for large machinery including assembly lines, pumps, and compressors.
Practical Applications
Motor starters are important components in a wide variety of applications across multiple industries. Here are some of their practical applications:
- Automotive Industry: In this industry, they are used for applications such as robotic arms and assembly lines.
- HVAC Systems: Motor starter are used in air conditioning systems to control blowers, fans, and other motors, controlling airflow and optimizing energy use.
- Pumps and Compressors: They help in managing the start/stop sequence of pumps and compressors in the oil and gas industry as well as in water treatment facilities.
- Industrial Manufacturing: They are used to operate large manufacturing machines such as mixers, grinders, crushers, and conveyors.
Tips for Choosing the Right Motor Starter
Starters come in a variety of models, types, and specifications to suit a wide range of requirements for different industries, settings, and contexts. As such, finding the right fit for your unique requirements can be a challenge. Here are some considerations to keep in mind when selecting a motor starter:
- Specifications
To determine the capacity of the starter you need, check the full load amperage (FLA), horsepower (HP), and voltage. It is also important to consider the starting torque, choosing variable frequency drives (VFDs) or soft starters for high-torque applications.
- Application
Choose a duty cycle that takes into consideration the frequency of use since frequent starting and stopping can cause higher thermal stress and wear over time. Think about the environmental conditions where you will use it, taking into account factors like extreme temperature, dust, and moisture levels, choosing a starter with suitable ratings and enclosures. Consider whether the application requires variable speeds, reversing, or multiple speeds and select the right fit.
Get Help from Our Experts at Essential Electric Supply
Understandably, choosing from the vast range of starter options can be daunting. Our team of experts at Essential Electric Supply is here to help.
Our collective experience in electric parts and supplies spans more than three quarters of a century and our staff members are highly knowledgeable and friendly. No matter what your unique needs are, we are always available to discuss the options and help you get the right solution.
All our parts come with a gold standard two-year warranty, proof that you can always count on us to deliver quality. Thanks to our focus on giving customers the best possible experience, we always deliver in the shortest time possible and at the best price. Talk to us today to get the best quality motor control starter and any other electric parts.
