IRR-3 Relay unit
From Zenitel Wiki
The IRR-3 relay unit (item 1020600992) is used in combination with industrial stations. The relay unit is used for operating of rotary light or sound device for call indication. It can also be used for switching of 100V loudspeaker lines.
IRR-3 operated from a centrally located relay
Wiring when the relay is located by the AlphaCom exchange.
IRR-3 operated from a locally located relay
Wiring when the relay is located in the remote station.