Normally closed contacts in magnetic latching relays: working principle and application analysis

1. Basics of magnetic latching relays
As the name implies,  magnetic latching relaysare relays that maintain their working state (closed or released) through the action of a magnetic field. Compared with traditional electromagnetic relays, magnetic latching relays do not need to be continuously powered on to maintain their state after actuation. Only a short pulse current is required to change their state, which greatly saves energy consumption. This feature makes magnetic latching relays particularly suitable for applications that need to maintain a certain state for a long time, such as remote control, automation equipment and power systems.

2. Working principle of normally closed contacts
In the structure of magnetic latching relays, contacts are one of its core components and are responsible for the on and off of the circuit. According to the state of the contacts when the relay is not actuated, they can be divided into normally open contacts and normally closed contacts. Unlike the normally open contacts that are in an open state when not energized, the normally closed contacts are in a closed state when the magnetic latching relay is not energized or not actuated. This means that under normal conditions, the two contact parts of the normally closed contacts are in contact, allowing current to pass freely and maintain the connection of the circuit.

When the coil of the magnetic latching relay receives a power-on signal and generates a magnetic field of sufficient strength, this magnetic field will act on the armature (or moving iron core) inside the relay. The armature is displaced by the magnetic field force, moving from its original position to a new position separated from the contacts. In this process, the normally closed contacts that were originally closed are opened, the circuit is disconnected, and the current cannot continue to flow. It is worth noting that once the armature is attracted to the new position by the magnetic field, even if the coil is powered off, due to the design of the magnetic circuit (usually including permanent magnets), the armature can remain in this position, that is, the relay remains in its current state until it receives a reverse pulse signal to change its state.

3. Application advantages of normally closed contacts
Safety: In circuits that require emergency power off or fault protection, normally closed contacts are used as the default closed state, which can immediately cut off the circuit when the relay fails or the power is lost, thereby improving the safety of the system.
Energy saving: The low-power holding characteristics of the magnetic latching relay, combined with the use of normally closed contacts, can significantly reduce energy consumption in applications where the circuit is kept disconnected for a long time.
Reliability: Since the normally closed contacts are in a closed state when not in action, the probability of failure caused by poor contact is reduced, and the stability and reliability of the system are improved.
Flexibility: By programming the action of the magnetic latching relay, the remote control and automatic management of the circuit can be flexibly realized, which is suitable for complex control systems.
IV. Practical application cases
Smart home: In smart home systems, magnetic latching relays are often used to control the power on and off of lighting, curtains, air conditioners and other equipment. Normally closed contacts ensure that the power is automatically cut off when the control system fails to ensure safety.
Industrial automation: In automated production lines, magnetic latching relays and their normally closed contacts are used to control the start and stop of motors, sensors and other equipment to achieve efficient and accurate production control.
Power system: In power systems, magnetic latching relays are used as protection relays. They use normally closed contacts to quickly cut off the faulty circuit in case of a fault to prevent the accident from expanding.