What is a pointer relay?

In automation and telemechanics, in operational circuits, devices such as a pointing or signal relay are used. They occupied their niche in the field of visual information and warning about certain parameters in operational control schemes. When triggered, the device visually changes: “the flag falls out”, “the blinker is turned”, “the dog is triggered”, etc. The design can additionally be equipped with several pairs of movable contacts, which change their position together with the signal mechanism. In this article we will consider the device, the principle of operation and the purpose of the indicator relay.


Products are intended to inform about the reasons for blocking or de-energizing operational control schemes, in case parameters go beyond certain limits.

REU photo

For example, a sudden inrush of current or voltage triggers a product that signals about what happened, with further disassembly of the operational circuit or a warning on the operator’s light panel. This is necessary so that the maintenance staff can quickly respond to an emergency situation and eliminate the causes.

Operating principle

The mechanism of the device is represented by a latch with a spring, which is forcibly cocked and fixed until the electromagnet trips. He, in turn, will release the latch with the spring, closing or opening the contacts and visually signaling to the personnel about the fact of operation.

Consider the principle of operation of the device on the example of the relay RU-21:

Appearance of RU-21


Application area

The indicative type of relay is used to signal emergency conditions in AC and DC networks. Also, the alarm system is used in circuits for measuring insulation, rated current, differential current and other parameters.

Wiring diagram for the organization of control of short circuit currents, through transformers TT:

Single-phase and interphase short circuit

We also recommend that you watch the video, which clearly shows what the RU-21 indicator relay consists of and how it works:

So we examined the principle of operation of the indicator relay, as well as the device and purpose. We hope the information provided was interesting to you!

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