Latching Relay: Working principle, Advantages, Applications

In many applications, it is important for the customer to conserve electrical energy. One approach to energy conservation is to use a latching relay that does not require constant power to maintain contact closure. Hence, the definition, working principle, and advantages of a latching relay should be known by all electricians.

What is a Latching Relay?

The latching relay is a control device that operates on an impulse control signal. At each brief impulse applied to the coil, there is a change in the contact’s status which therefore remains in position without the need for a continuous coil power supply.

It can be operated manually, remotely, from several control points, or by impulses. Latching relays are most frequently used for the control of lighting circuits in various public places with multiple control points.

A latching relay is also referred to as “bistable relay” or “impulse relay”

How Does a Latching Relay Work?

The latching relay closes or opens its contact every time a mains voltage pulse is applied to its coil terminals. The pulse is generated by depressing one of the pushbuttons. All the pushbuttons are connected in parallel.

Using latching relays the zone’s lighting circuit can be operated from several locations. It is well appreciated in corridors, staircases, and large rooms.

Using latching relays instead of contactors in lighting circuits no coil needs to be powered, with a saving of around 2W per relay. The global energy saving for each relay is greater than 5 kWh a year (for average use of 8 hours a day). The latching relays permit, moreover, the control of the lighting with an unlimited number of pushbuttons. The realization of the circuit with parallel keys is very simple! This makes it particularly suitable to be used in more complex lighting plants, when, for example, the sequential control of the utilities via a single circuit of pushbuttons is required.

These devices can be used to realize innovative solutions, ensuring the maximum saving of energy, thanks to their design philosophy, which consumes only a brief period of the duration of the impulse control.

Resetting a Latching Relay

You can reset a latching relay using the actuator. The latching relays are equipped with a manual actuator and a selector that cut off the coil supply putting the system out of service, for example in the case of maintenance.

Advantages of Latching Relay

The benefits of the latching relay are the following:

• It saves crossbar switches; the lighting can be controlled by push buttons instead of a combination of the crossbar and three-way switches.
• It saves conductors. it is possible to use smaller cross-sections for the control circuit than for the power circuit.
• It brings higher comfort of control; for example, it is possible to switch off all lights when leaving the house.
• It offers silent continuous operation compared to the same application using contactors. The distribution board can be installed in quiet rooms (bedrooms, offices) without disturbing users.
• It saves energy. When the remote control is needed, the impulse relay is the equipment with the lowest self-consumption. This is because energy is only needed to change its state from ON to OFF, OFF to ON. No energy is needed to maintain the ON state.
• Latching relays control more lamps than contactors of the same nominal current.
• It needs less time to connect the devices.
• It is a low-cost device.

Latching Relay Diagram

Below you can see the wiring diagram of a latching relay: