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.
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.