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Start-stop Circuits: Everything You Need To Know

A start-stop electric circuit controls electronic systems, leading to safer industrial processes. In that case, it allows you to run and stop a system, which includes machinery. Additionally, this may involve a two-wire or three-wire configuration for various applications. For example, it may be installed in conveyor belts and jog motors. Understanding the start-stop circuits and their capabilities can also lead to many different creative projects. After reading this article, you will learn more about this circuit type and how it works. So let’s get started!

What Is A Stop-start Circuit?

Conveyor belts feature a start-stop circuit for controlling processes.  Conveyor belts feature a start-stop circuit for controlling processes. 

The start-stop circuit is a circuit with integrated single push buttons for starting or stopping electrical components, equipment, or motors. These electrical circuits also feature a combination of overloads, relays or contactors, and contacts. You can typically find these connected to machinery, such as conveyor belts, with control circuits. Generally, a control circuit determines when a component or motor should begin and cease operations.

Components Used in Start-stop Circuits

A start-stop circuit generally relies on various connected components to function. These include buttons/contacts, relay/contactor, motor, and overload.

Buttons/Contacts

Image showing a single push button switch.  Image showing a single push button switch. 

Start-stop circuits rely on a push button and contact for electrical power distribution. These also rely on logic gates to start or stop operations for any provided application.

Relay/Contactor

A close-up photo of an electric relay. A close-up photo of an electric relay.

A relay or contactor controls components connected to the contactor or relay. In this case, a contactor’s coil connects to the control circuit’s lower voltage. Pressing the button provides power to the ring. Meanwhile, a motor receives voltage.

Motor

Electric motor coil Electric motor coil

An electrical motor, which generates kinetic energy, provides start-stop functionality on a circuit. For example, it can control conveyor belts and process machinery movements.

Overload

Start-stop circuits feature overload protection to prevent damage to the circuit.  Start-stop circuits feature overload protection to prevent damage to the course. 

Components need protection against overcurrent and overvoltage, so a circuit generally features an overload device. An example could include overload relays.

The Electrical Supply Required For A Start-Stop Circuit

Many control circuits rely on control voltage measuring 24V DC (direct current). Of course, start-stop circuit voltage levels vary based on the following factors: component configuration and overall controllability. A start-stop electrical circuit controlling the contactor coil (24V) won’t require a control voltage connection to the motor supply voltage. Overall, this results in a low control voltage. Connecting a three-phase motor will cause the supply voltage to send power to the contactor. Afterward, the coil determines when the contactor supplies power to the engine. Contacts with higher current loads connect to a motor. For example, a 240V connection can control a single-phase motor. 

How Does A Start-stop Circuit Work?

These circuit diagrams provided will help you understand how a start-stop circuit works.

Current flows throughout the circuit after pushing the start button. Current flows throughout the circuit after pushing the start button.

The red highlighted area demonstrates the start-stop circuit’s current flow path. Typically, a control circuit will have a voltage rating ranging from 24V – 400V. The control functionality relies on 24V in this case.

The relay or contactor coil sets to an active state.  The relay or contactor coil sets to an active state. 

The current will pass through once you push the start button. Afterward, the relay or contactor coil sets to an active state. A contactor provides motor control capabilities. Stimulating the contactor sends current to the motor, allowing it to operate. The contact becomes powered up after the relay or contactor coil energizes. In turn, the circuit sets to a closed position, which means you can release the button, and the current will still flow. Otherwise, the course remains fully functional until you press the stop button or if a fault occurs.

Pressing the stop button (closed position) stops current flow throughout the circuit.  Pressing the stop button (closed position) stops current flow throughout the circuit. 

As implied, pushing the stop button, also called the closed position, prevents continued current flow throughout the circuit. In turn, the coil loses power, causing the course to open. Moreover, you can make the circuit functional again by pushing the start button.

Ways To Control The Wiring In A Start-Stop Circuit

You can control the start-stop circuit’s wiring with two configurations: two-wire and three-wire control.

Start-stop Circuits: 2 Wire Control

A two-wire control has a control device with contacts intended to either activate or deactivate the pilot device. These also require minimal current levels to operate since larger loads, which rely on more connections,  could damage the circuit. Therefore, two-wire controls have applications for controlling motors or lights. Releasing the button for this configuration opens the coil, implementing closed contact to ensure functionality.

Start-stop Circuits: 3 Wire Control

Example of a three-wire control position. Example of a three-wire control position.

The start/stop control position circuit is an example of a three-wire control circuit. Generally, it relies on brief contact, start/stop stations, and a seal that opens upon contact. This contact connects to the start button in parallel, controlling the voltage that the coil receives. This configuration contains fewer components than the two-way control circuit, resulting in different functionality.

Other Start-stop Circuits

You can also create other start circuit projects. We will look at the start-stop jog circuit, one with a connected motor.

Start-stop Jog Circuit

A start-stop circuit diagram with jog input. A start-stop circuit diagram with jog input.

Pushing the start button will cause the current to flow through the push button and seal-in contact. Next, the contact manages coil power distribution. So you can release the start button without interrupting the current flow. Pushing the start button will cause the current to flow through the push button switch and seal-in contact. Next, the contact manages coil power distribution. So you can release the push button switch without interrupting the current flow. You can de-energize the motor's coil through varying methods. If the motor overloads, then the contacts will open. Pushing the stop button will prevent power from reaching the seal-in contact, leading to a de-energized coil. Another option for closing the control circuit involves placing the switch in the jog state. It, in turn, de-energizes the lock. As a result, the seal-in contact will no longer supply power to the device. You will need to push the start button to re-energize the coil.

Start-stop Circuits With A Motor Connected

Current flows throughout the circuit after pressing the button, activating the motor. Current flows throughout the circuit after pressing the button, activating the motor.

As you can see, the motor begins operating whenever current passes through a contactor coil.

Letting go of the start button or pressing the stop button stops the current flow. Letting go of the start button or pressing the stop button stops the current flow. The current will no longer flow throughout the circuit after you release the start button. Pressing the stop button also results in that effect. The motor will not run without applied power as a result.

Summary

Industry and automotive workers should remain as safe as possible, especially when dealing with specific systems. Therefore, understanding a control system and how it works can lead to an accident-free experience. So particular processes can be started and interrupted at any time by pressing a single push button. With automation tasks constantly advancing, control circuits will become more accessible in machinery. Therefore, it’s a good idea to utilize automated systems in the best way possible. Do you have any questions regarding the start-stop circuit? Feel free to contact us!