The Function of Annunciator Relays

Posted on February 12, 2021 linda strong aviation

An annunciator relay is a device used to indicate dangerous states and operating conditions in control rooms, on control panels, and in mimic diagrams. Annunciator relays feature a robust construction that ensures they are reliable and also suitable for use in harsh ambient conditions. Annunciator relays provide three distinct advantages. For one, their pre-configured messages provide time-saving startup and use. Secondly, their robust mechanical construction ensures reliable and durable use. Finally, individually pre-assembled contact assignments make it available to use in a broad range of applications. There are two types of annunciator relays: semi-automatic and fully automatic. This blog will explain both as well as the most common annunciator designs.

Semi-automatic Annunciator Relay

The semi-automatic relay features a coil excitation voltage and no other auxiliary voltage. This is an important aspect of the semi-automatic annunciator and is very important in voltage monitoring applications. During normal operation, the indicator flag area remains black. The white field of text appears once the relay has been triggered. At this point, the contacts also switch to the operating position. The user acknowledges this message by pressing the reset button on the front of the device. Once acknowledged, the text field remains in sight, but an additional red and white hatched indicator flag is displayed.

At this point, the contacts return to their normal position. Upon clearance of the malfunction, the indicator flag also returns to its normal operating position. In addition to the aforementioned function of the relay’s contacts, additional contacts can be switched manually. These contacts operate separately of the acknowledgement function, and the required switching function (normally open or normally closed) is set at the factory and can be changed later.

Fully Automatic Annunciator Relays

Fully automatic annunciator relays are most commonly used to indicate dangerous states and dangerous operating conditions. It is fully automatic, and therefore there is no manual reset function. Depending on the switching action, the relay switches to and from the triggered position when it is energized or de-energized. This switches the contacts and causes the indicator flag to appear. Once the malfunction has been cleared, the indicator flag disappears automatically and the contacts return to their normal position. Like a semi-automatic annunciator relay, the required switching function of normally open or normally closed is set at the factory. However, the switching function of fully automatic annunciator relays cannot be altered later.


Generally speaking, there are three designs of annunciator relays: surface-mounted, flush-mounted, and a combination of the two. In the surface-mounted design, the relay includes a DIN rail fastener of 35mm with a connector plate and clamp. The annunciator relay is mounted on the surface of the device it is used on. Flush-mounted annunciator relays, the design features a switch panel mounting with a clamping frame. The contact’s protective cap conforms to the device on which it is attached, creating a flush appearance. Regardless of the type or design of the annunciator relay you need, the device will play an important role in controlling an electrical system. As such, ensure you are getting them from a trusted source like Aviation Sourcing Solutions.

Aviation Sourcing Solutions is a premier supplier of all types of aviation parts as well as NSN parts, electronics parts, and much more for various military and civilian applications. Owned and operated by ASAP Semiconductor, we can help you find all types of unique parts for the aerospace, civil aviation, and defense industries. Our dedicated account managers are standing by and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at or call us at 1-714-705-4780.

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