The RKO-3 relay is meant for use in power supply circuits of heaters located in cable cases and cabinets with automation. The relay may also be used in circuits of other devices, where control over power supply continuity is required. The RKO-3 relay is intended to check current flow through three supplying circuits. This can be a 3-phase circuit or three single-phase circuits.

In case of loss of current flow signalling contacts of a set phase are made.