Magnetic Starter Power Supply Modes & Standard Wiring Guide

Industrial motor control systems utilize electromechanical switches called magnetic starters to assist in safely powering on and off electric motors. In order for electric motors to be operated safely and efficiently, it is imperative that one has a proper understanding of the modes of operation and wiring standards that are established for magnetic starters. This document provides an overview of magnetic starters as well as outlines the two standard power supply modes, Direct-On-Line (DOL) and Star-Deltastarting methods as well as provides a wiring guide for the industries employing these devices.

Overview of Magnetic Starters 

magnetic starters are used within the industry as a means of controlling high-voltage motors. A magnetic starter consists of a contactor (power connection device) and an overload relay (protective device against excess current and overheating), which are packaged together in one housing. Due to the high level of safety and reliability of magnetic starters, they are utilized by the manufacturing, HVAC, and water treatment industries (among many others) to control the operation of large motors used within their facilities.

Two Standard Power Supply Modes 

magnetic starters magnetic starters can operate with two different modes of power supply. These two modes are Direct-On-Line (DOL) and Star-Delta, which are the accepted standards of the industry. In order to ensure proper use for industrial applications, the following will provide an overview of each of these two methods.

1. Direct-On-Line (DOL) Starting

DOL starting is the most straightforward and commonly used method for starting electric motors with a horsepower rating of 5HP (3.7 kW) and below. When the DOL starting method is used, a motor is applied with full line voltage immediately upon start-up. As a result, DOL starting produces maximum torque as soon as the motor is started.

Advantages - Simple circuit and easy installation - Produces maximum torque of the motor when started - Ideal for small motors (those requiring low current)

Disadvantages - High inrush current produced when starting the motor may produce a temporary drop in voltage levels throughout the facility. Increasing mechanical stress on motors that are electrically connected to other electrical equipment.

Things to Consider:
Compressors, pumps, or a fan that requires a large amount of starting torque

2. Star Delta Starting:
Star-Delta starting is a method used for most motors above 5HP or greater than 3.7kW. Motors start in a star configuration where the initial voltage is at a lower voltage and lower current than during a delta operation, which is run at full voltage when completed. Once the assigned time has lapsed, the starting device will change the motor from star to delta configuration and run the motor at full voltage.

The advantages to this method of starting are that it reduces the amount of starting current, reducing the chance of having a voltage drop. Also, it reduces the amount of mechanical stress on both the motor and load during start-up.
The disadvantages of this method include more complicated wiring in comparison to Direct On Line DOL starting, and Star Delta starting is not a suitable method for applications due to high starting torque.

-Examples: Pumps, conveyors, and mixers where lower starting torque is required.

Standard Wiring Guide for magnetic starters
magnetic starters can be effectively utilized by proper wiring when completing the following standard wiring steps:

magnetic starter Inner Workings and How They Are Wired:
 Contactor: Connects and disconnects power to the motor
 Overload Relay: Protects from overload, low current, and overheating.
 Control Circuit: Push buttons to manually start or stop a motor.
 Circuit Breaker (recommended): Protects a motor and starter from damaging short circuits or catastrophic failures due to faults.

Wire Step by Step:
1- Power Supply Connection: Connect incoming power supply lines to the input terminals of the contactor-L1, L2, L3. Use the same gauge of wire as the motor's power needs.

2- Connect Motor: Connect the motor terminals to the output terminals of the contactor. Utilize the wiring diagram provided with the motor to avoid motor misconfiguration.

3. Wiring would need to be done so that the Overload Relay is installed in series after the output of the contactor. The trip point of the Overload Relay will be the full-load current rating of the motor for maximum protection.

4. The push buttons can be wired so that there are start (normally open) and stop (normally closed) manual controls. Auxiliary contacts on the contactor can be used to ensure self-latching functions of the control circuit.

5. To protect against an electrical fault, a circuit breaker should be installed upstream from the magnetic starter. As a general rule, the circuit breaker should have a rating for the voltage and current of the motor.

6. Upon completion of the wiring, make sure that the system is functioning properly. Verify that all electrical connections are secure and that the motor both starts and stops as intended. In addition, check the voltage levels at each point in the overall system to prevent any potential malfunctions. Safety Tips for Installing Magnetic Starters - Follow Local Electrical Codes: When installing magnetic starters, always follow national and local laws governing the installation.

- Use Personal Protective Equipment: While working on the installation or maintenance of the starters, you should wear insulated gloves, goggles, and any necessary protective equipment. - Conduct Periodic Inspections: Perform periodic inspections of the starter to determine if they are showing signs of wear, thus eliminating possible failures in the future.

 FAQs

Q1. What is the difference between a magnetic starter and a circuit breaker?

A. A magnetic starter provides start-stop control of a motor and provides low-current overload protection, while a circuit breaker cuts off power due to a short circuit or when there is a fault of a severe nature. Both devices work together to ensure the motor functions correctly and safely.

Q2. Is it possible to use a magnetic starter without a circuit breaker?
You could do so but it is not a good idea, as the circuit breaker protects from shorts, as well as large faults.

Q3. When would I use DOL or Star/Delta starting?
If you have a small(<5HP/3.7kW) motor that requires high starting torque, you would use DOL. If you are starting a large motor or a system that is sensitive to voltage flicker, then you would use Star/Delta.

Q4. How often should I check my magnetic starter?
You should check it at least once every six months, as well as perform visual checks every day, or as needed per the manufacturer's recommendations. Visually checking for problems with your starter on a regular basis can help you to identify visible issues before they become a problem.

Magnetic Starters with Circuit Breakers Have the Best Protection for Electric Motors.

Having a magnetic starter and circuit breaker combination, combined with a comprehensive motor protection scheme, gives the best protection to an electric motor. The circuit breaker protects the system against short circuits and severe faults, while the magnetic starter provides controlled starting and stopping of the motor. Together, these devices reduce the risk of mechanical damage to the motor, electrical hazards, and downtime.

Always use a (high-quality) correctly rated circuit breaker with your magnetic starter for optimum performance.

Summary

Understanding the difference between DOL and Star/Delta starting and how to wire them correctly with a magnetic starter is important to safely operate and effectively use electric motors in industrial applications. Magnetic starters are dependable power-controlling devices. However, when used together with a circuit breaker, their reliability greatly improves. You will be able to increase the longevity of your motor and improve the safety of your workplace by using the right components and following wiring best practices.

For help with your magnetic starter or to view our large selection of matched magnetic starters and circuit breakers, please call our technical team.