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 746 became telephone 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. |
N8722 | |
| 8741 | Cord Conn No. 4/501 4000 ohm ringer fitted. |
N8741 | |
| 8746 | Cord Conn No. 4/502 4000 ohm ringer fitted. |
N8746 |
| BACK | Home page | BT/GPO Telephones | A - Z Index | Glossary of Telecom Terminology | Quick Find | All Telephone Systems |
FM