Skip to content 
An electromechanical relay is a switching device that uses an electromagnetic coil to mechanically operate a set of contacts. This allows a small electrical signal to switch a larger load circuit on or off, providing electrical isolation and control in a compact device.
Now, let’s explore the 9 steps of the electromechanical relay working principle to understand the sequence of events that enable this switching action.
9 Steps of Electromechanical Relay Working Principle
| Step Name | Description |
|---|---|
| Input Electrical Signal | Low-power electrical signal is applied to the coil terminals, typically from a control circuit or sensor. |
| Coil Energized | Current flows through the coil winding, creating an electromagnetic field around the ferromagnetic core. |
| Magnetic Field Attracts Armature | The magnetic field magnetizes the core and attracts the armature (movable iron piece). |
| Armature Moves | The armature moves toward the coil assembly, initiating the change in contact state. |
| Contacts Open/Close | Armature movement causes the contacts to make or break the connection between terminals (NO/NC). |
| Circuit Switching Completed | Contact position change completes or interrupts the load circuit, controlling high-power devices. |
| Electrical Isolation | Isolation is maintained between coil (control side) and contacts (load side) for protection. |
| Coil De-energized | When input stops, the coil loses power, and the electromagnetic field collapses. |
| Spring Returns Armature | A spring returns the armature to its original position, resetting the contacts and completing the cycle. |
Input Electrical Signal
The relay begins to operate when a low-power electrical signal is applied to the coil terminals. This signal is typically from a control circuit or sensor.
Coil Energized
The input signal energizes the coil, causing current to flow through the wire winding around a ferromagnetic core. This creates an electromagnetic field.
Magnetic Field Attracts Armature
The electromagnetic field generated by the coil magnetizes the core, producing a magnetic force that attracts the armature—a movable iron piece connected to the relay contacts.
Armature Moves
Under the magnetic pull, the armature moves towards the coil assembly. This mechanical movement is the key action that changes the state of the relay contacts.
Contacts Open/Close
As the armature moves, it either makes or breaks the electrical connection between the common terminal and the normally open (NO) or normally closed (NC) contacts, depending on the relay configuration.
Circuit Switching Completed
The change in contact positions completes or interrupts the load circuit, allowing the relay to control high-power devices such as motors, lights, or industrial equipment using a low-power input.
Electrical Isolation
The relay maintains electrical isolation between the coil (control side) and the contacts (load side). This protects the sensitive control circuit from high voltages and currents in the load circuit.
Coil De-energized
When the input signal stops, the coil is de-energized, causing the electromagnetic field to collapse and removing the magnetic force holding the armature.
Spring Returns Armature to Original Position
A spring connected to the armature pulls it back to its default resting position, resetting the contacts to their original state and completing the cycle.
Conclusion
The electromechanical relay working principle relies on the conversion of an electrical input signal into mechanical movement, allowing it to switch high-power circuits safely and reliably. Understanding these 9 steps provides clarity on how relays function in diverse applications—from industrial automation to household appliances.
Electromagnetic relays remain invaluable due to their robust design, electrical isolation capabilities, and precise switching performance. Whether you’re designing control systems or troubleshooting circuits, grasping how an electromagnetic relay works is crucial for effective and safe electrical system design.
