NEC Electra Elite 48/192 Features And Specifications Manual page 339

Issue 6
E - 36
The External Tone Ringer does not operate on a trunk that is not
¥
assigned to a Tenant group.
General:
¥ An ECR-U10 ETU is required for common audible and control relays
(10 relays are provided).
The external ringing equipment must be locally provided.
¥
¥ Incoming calls to an External Tone Ringer can be answered by Call
Pickup (Intratenant/Intertenant).
Electra Elite
External Tone Ringer