User:RHaworth/Charging group

In the UK telephone system a charging group (the term used by the GPO) or charge group is a group of exchanges having the same list of call charges.

++++ pending this author's discovery/development of a Wiki Template for the purpose, ++++ is used to mark a point where expansion or clarification is needed.

Description
Charge groups were introduced in 1958 at the same time as Subscriber Trunk Dialling (STD). (Before that, each exchange had its own set of call charges - a charge matrix with 18 million entries and only primitive computers to handle it. The White Paper ++++ footnote identified simplification of the charge matrix as an important pre-requisite of STD.)

A charge group covers an area of roughly 7 miles radius containing a dozen exchanges on average. The London Director charge group is the exception: it contains all exchanges within 12&frac12; miles of Oxford Circus. All exchanges within a charge group have the same call charges: calls within the charge group are Local rate and with a few exceptions (see below) calls to adjacent charge groups are also Local rate.

Beyond that calls were trunk calls. The calls for these were based on the direct-line distance between charging centres. The charging centre was an exchange (which gave its name to the Charge Group) near the centre of the group. Often, but by no means always, it was the switching centre for the group. ++++ Improve wording. Calls were charged at 'a' rate (up to 35 miles = 56 Km), 'b' rate (35 miles to 50 miles = 80 Km) or 'c' rate (over 50 miles). (See also Demise below.)

Adjacent but non-local
The size of charge groups was selected so they would be roughly the same size (with London allowed to be an exception) and that each market town would be at the centre of its own charge group. ++++ Middle Ages This pattern which worked well across the English Shires but began to look rather strained in hilly areas.

adjacent but non-local or adjacent but non-contiguous in the GPO terminology. For example Glossop to Hathersage across the High Peak of Derbyshire.

++++ move to chat: Rod Sladen reported that at the television transmitter at Holme Moss high on the Pennine moors between Lancashire and Yorkshire, there are two telephones on the engineer's desk (in case one is not working in an emergency). One is connected to the nearest exchange to the east: Holmfirth in the Huddersfield Charge Group and the other to the nearest exchange to the west: probably Glossop in the Glossop Charge Group. These two charge groups are 'contiguous but non-adjacent' so a call from one of these phones to the other would be an 'a' rate trunk call.

Maps
Once it had been drawn, the map of Charge Group areas was converted into local lists of exchanges by Charge Group and, for each Charge Group, what other Charge Groups were Local, 'a' rate, and 'b' rate. There were no changes to the map thereafter (apart from two minor ones discussed below). Hence the map disappeared from view. But two versions of it can be found on the web:


 * The 'GPO' Map - (1896 x 3460 pixels and about 300K bytes) with the List which provides the key to the Charge Group numbers shown on the Map
 * The 'GWR' Map - (PDF - 188K bytes) - with a note on its provenance
 * Further resources can be found in this article's discussion page

The GPO Map was probably drawn in 1957 or 1958 and never revised. The GWR Map is an accurate copy of the GPO Map and is a much clearer image but unfortunately it does not show Northern Ireland, the Isle of Man, Orkney, Shetland, the Channel Islands or Uckfield.

The GPO List is arranged alphabetically within Regions: The List as linked to here is a good reproduction of the paper original. But a few comments have been 'pencilled in'. Some are discussed below. The others - 'now &hellip;' - are changes of name between the original list and the Ofcom list of 2002. These are mostly ++++ ++++ change the list itself. ++++xref to list in demise.

Variations from Plan
There were scarcely any changes to the pattern of Charge Groups once the map had been drawn. Indeed the network was altered to fit the plan rather than vice-versa. For example Lodge Hill discussed below probably had few, if any, circuits  direct to Orpington before STD - calls from further afield would be routed via Croydon. After STD, any call dialled using the STD code would be routed via Orpington and more circuits were therefore provided from there to Lodge Hill.

Only two changes from the original plan have been noted (and these smack of Scottish region making a small revolt against control from London):

Group SC 51 Eigg (0836) is listed and shown on the map as covering the islands of Eigg, Rum, Muck, Canna, Sanday and Soay. It is shown as non-local to everywhere. ++++ Mallaig (0687)

Group SC 139 is listed as Salen. This group ended up containing just Glenborrodale and Kilchoan (0972) on the Ardnamurchan peninsula. Salen itself landed up in Group SC 153 along with Strontian, Kingairloch and Morvern (0967).

Charge Groups vs Code Groups
In general one STD code (dialling code) covered one Charge Group and vice-versa but there were numerous exceptions. ++++

Demise
The history of telephony has seen a progressive simplification in call charges - at least as far as terrestrial calls go. The introduction of mobile phones, new services and deregulation means that the call charges list of today (examples) is an order of magnitude more complicated than in 1958.

Before 1958 ++++. Even in 1968 ++++ 'c' was three for op connected. The 'b' and 'c' rate STD charge bands were merged in the early 1970's to enable premium rate services (++++ what was the first?) to be implemented using existing charging equipment.

It is almost true to say that Charge Groups are now a matter of history. Consider this list of Residential Telephone Tariffs for the three telcos who actually provide lines - British Telecom (BT), Telewest and NTL. With all three, inland call charges are independant of distance.

++++ Kingston upon Hull still local publishes but not use 'a' rate matrix.

Even before the demise of Charge Groups the boundaries were getting blurred. In New Addington, a suburb of Croydon, a BT subscriber would get a number on Lodge Hill exchange in the Swanley Charge Group. They could call Sevenoaks as a local call but to call Watford would be an 'a' or possibly even 'b' rate trunk call. But a Telewest subscriber in New Addington would get a London number (020 8407 xxxx for example). For them Sevenoaks would be an 'a' rate call and Watford would be local.