FAQ - Electromechanical and Solid-state Relays - Difference between Standard Relay and Latching Relay

Q: What is the difference between standard relay and latching relay?

A: 

1.Standard Electromechanic Relay

A standard electromechanic relay has one operating coil and a number of contacts. When voltage is applied across the terminals of the operating coil, the armature of the relay is drawn towards the operating coil against a spring tension and the state of the contacts changes. 

Subsequently when the relay is de-energised, the armature goes back to initial position due to the action of the spring and consequently the contacts go back to their initial state.

2. Latching Relay

A latching type of electromechanic relay has two coils, one operating coil (same as standard relay) and one resetting coil. When the operating coil is energised, the armature is drawn towards the operating coil and is then held in that position by a mechanical latch. In this condition, if the operating coil is de-energised, the armature remains in latched position. To release the armature, resetting coil is energised, which basically releases the mechanical latch.

Latching type relay is used for circuit breaker contact multiplication, so that correct status of the breaker is always available, even when control supply voltage fails.

The key difference between non-latching and latching relays is how they maintain their state. A non-latching relay returns to its default position when power is removed, while a latching relay stays in its current position, held by a mechanical latch, even without power. Latching relays use two coils: one to set and one to reset making them ideal for applications like circuit breaker monitoring, where the state needs to be maintained during power loss.

Date/Revision History

First review 03/25/2024 V1.0

2nd Review 01/13/2025

Author:

Aimee Rivera, Technical Support Engineer

References

Technical Guide for General-purpose Relays