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A trial of the modern PST (Plug Socket Telephone) system, using captive line jack units, took place early in 1981 in Taunton & Carlisle. This section briefly studies the new socket types and the implications on British Telecom's monoploy of the marketplace. |
Plugs, Sockets and Telephones (PST)
Plan 4
This was the earliest form of plug, socket and telephone combination, which used round type plugs (jack 95s) and sockets. Under the plan 4 scheme, additional telephones could be hard wired too.
PST
A trial of the modern PST (Plug Socket Telephone) system, using captive line jack units, took place early in 1981 in Taunton & Carlisle. The scheme was introduced nationally for residential lines, at the end of 1981 and later on for business lines as well.
The modern socket system used LJUs (Line Jack Units) comprising of a Master Socket and Extension Sockets. All wiring had to be provided by British Telecom, there was no option for fitting your own extensions. Initially the extension sockets were 15p per quarter rental which included normal wear and tear maintenance. Later on this token rental was abolished. At this time, 'approved' plug-ended extension phones could be purchased from any supplier and legally used. However, it was still mandatory to rent the main phone (the prime instrument) from British Telecom.
The Prime Instrument
British Telecom lost the 'prime instrument monopoly' on 1 Jan 1985 and it was no longer mandatory to rent any apparatus from it. As the liberalisation of wiring policy continued, plug in extension kits (to an existing master socket) were legal from about Dec 1986.
The Network Terminating Equipment No. 5 (NTE 5)
Also from (approx) December 1986, the policy of customers installing their own extension wiring was under review and a new Master Socket or Network Terminating Equipment was devised. The NTE 5 provided a clear demarcation point between the incoming line and customers' own apparatus or extension wiring. A captive plug and socket arrangement with the NTE 5 allowed for any extension wiring to be easily disconnected from the exchange line, for testing, to prove a fault on the line side or the customer side. However, it was not until 2 February 1988 that customers were allowed to remove the front plate from the NTE5 and connect their own wiring! The NTE 5 was introduced on a phased basis as training and stores became available in each telephone district.
Here's an extract from a marketing note of the time... "Sufficient stocks of the NTE 5, the new network terminating apparatus, are available for the launch to take place in East Anglia District from 18.5.87. This launch has been delayed due to the late arrival of stores, and a technical problem which has now been resolved"
From 1st June 1988, British Telecom's version of the NTE 5 was renamed the Linebox. BT also withdrew extension sockets from the rental portfolio. Originally they had carried a rental of 15p per quarter and later this was reduced to zero. However, while the sockets were still rented, BT was obliged to maintain the wiring. After this date, faulty extension wiring (from master sockets) would carry a 'cost of works' labour charge for BT to fix, or the customer could pay for a conversion to an NTE 5 and provide their own new extension wiring. It served as an easy way to avoid disputes over maintenance of extension wiring as well as providing a clear demarcation point regardless of whether an NTE 5 existed.
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