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Contactors and Relays 101 – Comparison & Applications

August 15, 2023

Contactors and relays are both solenoid switches that operate in electrical circuits to help ensure the efficiency of the system. They have similar functions and constructions, which results in many people confusing the two and even using the terms interchangeably. At a basic level, the two components function to turn electrical circuits on and off with the biggest difference being their capacity to handle different levels of current.

A Primer on Contactors and Relays

Contactors move into open and closed positions to allow the flow of electricity throughout a circuit. Relays also allow or prohibit electricity from flowing through circuitry. However, they perform these very similar functions in different circumstances through different mechanisms. Let’s take a closer look.

What Is a Contactor?

A contactor is an electrical switch that’s commonly used to establish and interrupt electric circuits in high-power applications with amperage loads of more than 10A. Typically, contactors are designed to sit in a Normally Open (NO) configuration. When one end of the contactor isn’t making contact with the subsequent section of the circuit, the circuit is open and unpowered. But energizing the contactor moves it to a closed position, and the circuit is activated. As the current reaches a contactor, it excites the electromagnet enough to generate a magnetic field; that field is what makes the contactor move from an open position to a closed position.

Contactors, like other electrical components that manage high loads, need to have safety devices and features to prevent unwanted, incomplete, or stuck connections. For example, overloaded contactors can weld into a permanently closed position, allowing the circuit to stay on without oversight. Some safety features that can prevent this include springs. Spring-loaded contacts push the contactor back to a Normally Open position. Contactors may also have magnetic arc suppression features. Circuits can even have overloads, which are parts that connect to the contactor and stop the flow of power if the current is too high for a set period. Overloads are like fuses — they interrupt the flow of current to protect subsequent parts and systems.

Most contactors fall under this description. However, a subtype of contactor, called auxiliary contacts, provides additional power functions that support the contactor. They can be in a Normally Open (NO) or Normally Closed (NC) position.

Contactors offer fast switching capabilities for simple operations, and they can manage high loads without high power consumption.

Overview of a Relay

Relays are commonly available in both the Normally Open and Normally Closed configurations. They are built to handle lower-power functions with amperage loads of less than 10A. Because relays handle relatively low powers and don’t always demand an NO design, they often don’t have safety features like spring-loaded moving parts.

These relays are simple and offer galvanic isolation. Relays can convert the voltage as power passes through the circuit and facilitate circuit multiplication.

Common Applications

Contactors and relays are chosen for different applications based on the power demands of the application and the number of phases it requires. For example, relays are used for single-phase operations and connect to a neutral point. Contactors, on the other hand, are popular in three-phase applications to join two unconnected poles together.

Some common applications of contactors include:

  • Starting motors
  • Lights
  • Switching capacitor banks

Some common applications of relays include:

  • Controlling power loads and changing voltages
  • Motor control
  • Use in automotive applications

Contact Our Experts for Your Industrial Contact and Relay Needs

At SMP Engineered Solutions, we specialize in providing DC contactors our industrial clients can trust for safe performance in high-power applications. We’re world-class engineers with complete in-house engineering, testing, and assembly capabilities. Contact us today to learn more about our products or request a quote to start your order.

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