Relays Their Key Constituents and Operations

Relays are essential devices in the world of electronics and electrical engineering, acting as control units that allow for the management of high-power circuits with low-power signals. Relays come in various types, common examples including electromagnetic relays, reed relays, and thermal relays, each serving specific purposes. In this blog, we will explore the assembly and operating principles of these vital components, that way you can better understand them.

Electromagnetic Relay

One of the most common types of relays is the electromagnetic relay. It consists of several crucial components, the primary ones being the coil, armature, and contacts. The coil, typically made of copper wire, generates a magnetic field when current flows through it. This magnetic field attracts the armature, a movable iron piece, which is mechanically connected to the relay switch contacts. When the coil is energized, the armature is pulled towards it, closing the switch contacts and completing the electrical circuit.

The operating principle of an electromagnetic relay can be compared to a light switch in any building. When you flip the switch, it completes the electrical circuit, allowing current to flow and the lights to turn on. Similarly, in an electromagnetic relay, the coil acts as the switch, and its energization decides whether the circuit remains open or closed.

Reed Relay

Reed relays are a more specialized type of relay, featuring a hermetically sealed envelope containing two thin metal strips called reeds, which act as a switch. When an electromagnetic coil surrounding the envelope is energized, it creates a magnetic field that causes the reeds to come into contact. This closes the relay contacts, allowing current to flow. Reed relays are known for their fast response times, high reliability, and low contact resistance, making them ideal for applications where precision is critical.

The operating principle of a reed relay is akin to how magnets attract metallic objects. When you place a magnet near a paperclip, it attracts the paperclip due to the magnetic field produced. In the same way, a reed relay uses a magnetic field to bring the reeds into contact, completing the electrical circuit.

Thermal Relay

Thermal relays are unique when compared to other similar options, as they rely on temperature changes to operate. Generally, these relays protect motors and other equipment from overheating or overloading. The key components of a thermal relay include a bimetallic strip and a heater, the bimetallic strip being made of two different metals with different coefficients of thermal expansion, allowing it to bend when subjected to temperature changes.

The operating principle of a thermal relay is straightforward. The current passing through the heater generates heat, and as the temperature rises, the bimetallic strip bends, eventually making contact with a switch. When this contact is made, it triggers the relay to open the circuit, preventing further current flow. This is a safety feature that helps protect equipment from damage due to overheating.

In a way, thermal relays function similarly to a thermostat. When the temperature reaches a certain point, a thermostat activates a heating or cooling system to maintain a comfortable environment. In a thermal relay, it is the heat generated by the current that initiates protective action.

Applications of Relays

Relays are indispensable in various applications. For example, electromagnetic relays are commonly used in automation and control systems, such as in industrial machinery, HVAC systems and automotive applications. Reed relays, with their precise and low-resistance switching, are used in telecommunications, automatic test equipment, and medical devices. As a whole, thermal relays play a vital role in safeguarding motors and equipment from overloading in industrial settings.


As covered in this blog, relays are fundamental components in the world of electronics and electrical engineering. Understanding their key components and operating principles, whether they are electromagnetic, reed, or thermal relays, is crucial for designing and maintaining electrical systems. With everything readily available for purchase at any time on our website, you are encouraged to peruse our selection at your leisure while taking advantage of our online RFQ service to request quotes quickly and easily on items of interest that you come across. Once we receive and review a completed form, a member of our staff will contact you in 15 minutes or less to present a tailored solution for your comparison. Get started on the purchasing process today and see why so many customers steadily choose Integrated Parts Online for part fulfillment.


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