"Dave Plowman (News)" wrote
| Only 3 is actually required as this is the shunt wire (bell).
| 4 is a local earth not used much - if at all - these days.
| Think it was for party lines.

It depends on whether you follow the BS or BT numbering whether the ring is
on 3 or 4.

The earth was used for earth recall on PABX. Line jack units were never
fitted on party lines.

Owain