What is the difference between a relay and a contactor?

What is the difference between a relay and a contactor?

The difference between a relay and a contactor can be partially understood from their names - both are devices used for current control. Their most significant similarity lies in their working principle, which involves controlling the closure of circuits. However, a contactor operates by generating a magnetic field through the flow of current in a coil, causing its contacts to close. In contrast, a relay allows or blocks the controlled output circuit when an input value (such as voltage, current, temperature, etc.) reaches a specified threshold. Let's take a closer look at the analysis below.

1. Working Principle

- Contactor (Contactor) Working Principle

A contactor refers to an electrical device in industrial electricity that uses the magnetic field generated by current flowing through a coil to close the contacts, thereby controlling the load. The contactor consists of an electromagnetic system (iron core, static iron core, electromagnetic coil), contact system (normally open and normally closed contacts), and arc suppression device. Its principle is that when the electromagnetic coil of the contactor is energized, it generates a strong magnetic field, causing the static iron core to produce electromagnetic attraction to attract the armature and drive the contact action: the normally closed contact is disconnected; the normally open contact is closed, and they are linked. When the coil is de-energized, the electromagnetic attraction disappears, and the armature is released under the action of the release spring, causing the contacts to reset: the normally closed contact is closed; the normally open contact is disconnected.

- Relay Working Principle and Characteristics

A relay is an electrical device that, when an input quantity (such as voltage, current, temperature, etc.) reaches a specified value, causes the controlled output circuit to conduct or disconnect. It can be divided into two major categories: electrical quantity (such as current, voltage, frequency, power, etc.) relays and non-electrical quantity (such as temperature, pressure, speed, etc.) relays. It has the advantages of fast action, stable operation, long service life, small size, etc. Widely used in power protection, automation, motion, remote control, measurement, and communication devices.

A relay is an electronic control device with a control system (also known as the input circuit) and a controlled system (also known as the output circuit), typically used in automatic control circuits. It is essentially an "automatic switch" that uses a smaller current to control a larger current. Therefore, it plays a role in automatic regulation, safety protection, and circuit switching in the circuit.

2. Different functions

- The primary function of a relay is for signal detection, transmission, conversion, or handling. It typically operates with smaller currents in the circuit and is used in control circuits to manage weak signals.

- The main purpose of a contactor is to connect or disconnect the main circuit. The main circuit refers to a circuit whose operation depends on whether it is connected or not. The concept of the main circuit corresponds to that of the control circuit. Generally, the current flowing through the main circuit is larger than that through the control circuit.

3. The difference between a contactor and a relay

Relay: Used for control circuits, with low current, no arc extinguishing device, can operate under the action of electrical or non-electrical quantities. A relay often has several pairs of normally open/normally closed contacts, which can be used in different control loops. Its contacts cannot pass through high current and it is generally not used in power circuits.

Contactor: Similar to a circuit breaker, used in main circuits, with high current, equipped with an arc extinguishing device, generally only operates under voltage. In fact, the principle is the same, mainly the contact capacity is different. Relay contact capacity is smaller, the contacts can only pass through small current, mainly used for control. Contactor capacity is larger, the contacts can pass through large current, more used in the main circuit.

The principle of the contactor is the same as that of the voltage relay, just the load power controlled by the contactor is larger, so its size is also larger. AC contactors are widely used as power switching and control circuits. Relay is a kind of small signal control electrical appliance, it is used for motor protection or automatic control of various production machinery.

It is worth noting that the two have exactly the same working principle, and in some special cases, they can even replace each other. The difference is that the relay can pass through relatively small current, there are many types, generally only used for transmitting signals, mostly seen in control loops. And the current of the contactor is relatively large, besides transmitting signals, it can also control the on and off of the main loop.