See Plug and Socket for more information

When Plug and Socket wiring was introduced, the standard range of BPO telephones had to have their circuitry modified.  This was because the new plan wiring system was technically different from the old way of working.  New plan standardised the way telephones worked, in so much as all telephones were technically wired the same, whereas the earlier wiring systems involved different wiring practices, depending on the extension plan required.

Modified telephones were given the prefix 8, therefore Telephone No. 746 became Telephone No. 8746.

The line cord was replaced with a grey flat cord with a flat plug on the end, the ringer was made 4000 ohms and the telephone wired to the new required circuit arrangements.

Differences from the standard telephones are as follows:-

Telephone No.  Differences Diagram No.
8722 Cord Conn No. 4/504
3.3K ohm resistor added in line with tone ringer.
8741  Cord Conn No. 4/501
4000 ohm ringer fitted.
8746 Cord Conn No. 4/502
4000 ohm ringer fitted.


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Last revised: October 20, 2022