This topic describes the second incarnation of the HANDEL Nuclear Attack Warning system, known as Wire Broadcast System WB1800 and the carrier equipment designated Wire Broadcast System WB1400. WB1400 replaced both the Verbal Warning WB400 and Siren Control WB600, in areas with a flood warning system, it also replaced the WB601.
Home Office archive file HO393/63 tells us the "expenditure on new carrier circuitry (known as WB1400) from and including the CCPs is costing a total of £24.6 million between 1982/83 and 1987/88."
This is the first of a two part topic. Part one, describes the broadcast of national attack messages to the carrier control points, and the distribution through the BT network to the customers local exchange. Part two, covers the distribution from the final exchange to customers speech and siren receivers.
National Attack Warning Centres
I took the photograph below at Hack Green Museum, and kindly thank Graham Carlisle for the gallery photographs of the table mounted control console and rack mounted test panel, in this section.
The main source of the National Nuclear Attack Warning would be the Air Defence Operations Centre ( ADOC ) at Strike Command in RAF High Wycombe, with a back up at the Preston U.K.W.M.O. Sector Headquarters, located at Langley Lane, Goosnargh, Lancs. This table mounted unit would be used to issue the message to the 250 Carrier Control Points (CCP).
The operator would turn the safety interlock key switch.
Press the large Red operate switch.
The speaking clock would be removed from all the national distribution rings.
A one second burst of two simultaneous tones of 1200Hz and 1440Hz known as P+Q tones would be sent to sound the incoming message alarm in the CCP.
When the "Speak Now" light illuminated the operator would announce the message into the dual microphones. This would be conveyed to the injection exchange for distribution on all four of the speaking clock rings.
The control console, with its associated signalling equipment and transmission links to the speaking clock were collectively known as WB1800. The abbreviation 'WB' for wire broadcast, in this case broadcasting of audio messages and signalling tones.
The two control centres, each had two separate private wires ( X & Y ) to each of the two speaking clock units, one in London and the other in Liverpool. Whichever centre initiated the attack message, it would be sent along four separate paths in parallel, maximising the chances of it being transmitted over the speaking clock rings. Police Station carrier control points received their duplicated speaking clock feed from both London and Liverpool.
The desk mounted, operating console (Unit WB1800/1A) is wired back to the BT apparatus room, which contains rack mounted signalling equipment and power supplies necessary to make it function. A rack mounted version of the console, the 'Test Panel' (Unit WB1800/2A), is normally used for testing from the apparatus room, but could be used in an emergency. The printed circuit board in both these designs of control unit is designated a Unit WB1800/3A. Unfortunately the circuit diagrams for this equipment are not available in the BT Archives.
HANDEL Equipment Gallery
Quarterly Testing of HANDEL
Routine tests of the HANDEL Network were made on the 1st Wednesday in January, April, July and October at 0200 and 0215 in the morning. A member of the public happening to call the speaking clock at this time would have heard the innocent sounding test messages too.
In the BT film made for the introduction of WB1400, titled "Wire Broadcasting Systems for the Future", which may be found on the DEVELOPMENT of the NATIONAL WARNING SCHEME page, in the page-top menu. A routine test is made from the ADOC control equipment where the voice says 'Leeds' testing. During testing, town names other than the real locations High Wycombe and Preston, were picked at random.
BT Staff at each centre would conduct the testing program. High Wycombe at 2 a.m. and Preston at 2.15 a.m. Only minutes before the test, the BT engineers would each pick a town at random and use it in their broadcast message to police carrier control points. British Telecom testing from XXXXX.
The Carrier Control Card 1 'Peacetime Testing Action', Section 2.2 reads :
When one or both RED lamps flash and alarms sound. Lift both RED handsets. Listen to the spoken message. Replace RED handsets. Note name of town mentioned.
Complete the form 'Report on Routine Test on Handel Equipment' in duplicate at once and return it to Force Headquarters the same day.
Carrier Control Point - Second Generation WB1400
The United Kingdom is divided into 250 Warning Districts each served by a Carrier Control Point (CCP) installed in a Major Police Station in the district. Each CCP controlled the operation of Air Attack and Flood warning sirens and the broadcast of fallout messages within its local area.
The block schematic diagram shows how two private circuits from the telephone exchange carry the speaking clock in one direction and the 72kHz carrier in the other. In the previous topic we read how the speaking clock circuits would be used to distribute the attack warning broadcasts. These duplicated private circuits take different routes to avoid a damaged cable isolating the CCP at the police station. At the exchange the two incoming carriers are monitored and one selected for distribution.
A third private circuit is for bothway communication with the UKWMO Group HQ. The UKWMO is responsible for issuing fallout warning messages and an all clear when the radiation has fallen to a safe level.
The small Equipment Carrier WB1400 control unit 21½"W x 11½"D x 17"H shown below performs the same function as much two larger WB400 control units in the police office and two steel cabinets, each 1ft 10in wide x 1ft 2in deep x 6ft high in the police station apparatus room containing all the logic and signal generation equipment.
Each of the three handsets terminates a pair of wires from the Control Point Exchange (CPE). The two Red handsets are designated "X Path" and "Y Path" and have associated Red "Lift Handset" lamps and alarm sounder. Providing there are no line faults both handset alarms sound in response to a broadcast message from Strike Command, lifting either will stop both alarms. The Red handsets can only listen to broadcasts as there is no return speech channel.
The Black "Group" handset is for two way communication with the UKWMO Group Headquarters for the warning district(s) served by this CCP. When the U.K.W.M.O. Group calls the CCP, a white alarm lamp "Group Tele" and alarm sounder will continue until the black handset is lifted, or self cancel after 90 Seconds. To initiate a call to Group, the alarm lamp cover that also serves as a pushbutton is pressed, the local alarm sounds for the duration of the press.
The same two pairs of wires, the 'X' and 'Y' paths, used to bring the national warning to the Red handsets also return two separate feeds of the 72kHz carrier signal back to the Control Point Exchange (CPE). The carrier is modulated by either Police Officer's spoken messages or siren control signal. Mains fail alarms are signalled to the CPE over the 'X' and 'Y' path wires too.
In the CCP gallery, a close up shows the control switches on the CCP. The siren can only be activated when the "MASTER" locked rotary switch, located on the bottom right, is turned through 90° clockwise to the ON position. Verbal warning messages may be sent without the master switch being activated.
The two left hand keys are pushed upwards to initiate their respective siren activation "ATTACK WARNING" or "ALL CLEAR" sequence. The "CANCEL SEQUENCE" key stops an activation sequence before it has run its full course. The siren control signal sequence is heard through the grille above the keys. Remote siren receivers are controlled by a sequence of two audio tones, a guard or "G-signal" of 1500Hz and siren activation or "S-signal" of 2160Hz. To prime the siren receiver, the G-signal is pulsed twelve times of 0.4 seconds on and 0.4 seconds off. After the tenth pulse, the S-signal starts, its duration depends on the warning. For the Attack Warning, it is pulsed 4 Seconds on and 4 Seconds off or 60 Seconds continuously for the All Clear.
The same two keys pushed in a downward direction initiate a spoken broadcast to the warning receivers. The rotary switch under these keys allows either the "SELECT" group of receivers (Those used in ROC & UKWMO peacetime exercises) or "ALL" for every receiver (War Emergency and Police quarterly tests) to hear the message.
The sequence begins with either four (Select) or eight (All) pulses of 605Hz tone, known as the "W" signal which turns the receiver speaker on for at least 20 Seconds.
Next follows six seconds of either - rapid pips of the "CALL" sound - or the wailing of the"ALARM" sound.
After this, the "SPEAK NOW" light flashes for 7 seconds.
During this period either Red handset may be used to announce the message by pressing a small press-to-talk switch on the side of the handset. The "SPEAK NOW" light continues to flash during the message and for a further 7 seconds after the switch is released during which time a further message may be sent by operating the press-to-talk again.
Once the light stops flashing, it is necessary to operate either the Call or Alarm switch to make a further broadcast. Two modulation meters indicate to the operator the correct level for the spoken message. The needle should be within the thick black line area.
There is a difference between the terminology used on the CCP panel and the instructions. The ROC "Standard Operating Procedure, Annex P" refers to the four or eight "W" tones as the 'Call' signal. The CCP 'Call' signal of rapid pips is called the 'Alert' signal in the ROC operating procedure, and the CCP Instruction Card "Carrier Control Card 3". They do however agree on the wailing 'Alarm' signal.
The CCP Instruction Card telling the police officer how to use the panel is reproduced in the CCP gallery above this text.
During periods when the CCP is not being used it modulates the carrier with a soft beeping 'Monitor Tone'. This tone can be heard if the warning point presses the test button on the carrier receiver's loudspeaker. It purpose is to give confidence the receiver is working properly. It may also be heard for a short time after the end of a spoken message, before the receiver speaker turns off.
WB1400 Carrier Control Point Gallery
Carrier Control Point : Duplicated Control Units for Security
Two CCP control units in two separate locations are provided for security against equipment failure and damage. The ''Working' unit was located at the secondary location, normally an office environment. The 'Standby' control unit would be plugged in at the primary location, typically an equipment room or secure basement accommodation. The user instructions describe what to do under fault conditions. The cables between the secondary and primary locations are called the 'House Wiring' which is connected to the flexible lead exiting the bottom of the 'Terminating Unit WB 1400'
Extract from User Instructions
What to do if the normal control unit fails to indicate a confidence tick on both meters.
The 'Working' equipment is normally situated at the secondary operating location. Connect the equipment to the primary operating location 'Working' socket in place of the house wiring. If it then operates correctly the fault is in the house wiring and the equipment should be left operating at the primary location.
If the equipment still fails to operate connect the 'Standby' equipment to the 'Working' socket at the primary location. This equipment should then operate correctly.
Reconnect the house wiring to the 'Working' socket and install the 'Standby' equipment in the secondary operating position. It is important to inform British Telecom Fault Control if this action is taken.
Primary Location: Changeover Panel
The Terminating Unit WB 1400 is the hub of the system in the Police Station. Internally there are two power units which should be fed from different mains supplies to guard against a ringmain fuse blowing. Connection strips terminate the external wiring to the building's Main Distribution Frame (MDF) carrying the two HANDEL circuits and the UKWMO Group HQ circuit back to the exchange. Next to the power units are six test links (four red for HANDEL and two black for ROC) intercepting these circuits allowing BT to setup and test the CCP. Other connection strips terminate the internal cables to the Terminating Unit WB 1401 at the secondary location and the 100 hour reserve battery.
The reserve battery supply is only used if the mains fails. Housed in a wall mounted "Box Battery WB1400" it contains a "Terminating Unit WB1402" into which four "Battery Dry 101", rated at 18 volts, 20 Ampere Hour are wired in parallel. These are Lithium non-rechargeable batteries.
The flexible hose emerging from the bottom of the unit has a plug that is normally connected to the 'Working' socket. The reserve control unit's flexible lead is normally plugged into the 'Standby' socket. This may be changed around to isolate faults and maintain a working CCP.
Timings and Frequencies of Signals Generated by the CCP
The purpose of the various control signals generated by the CCP has been described earlier on this page. While the frequencies used and timing of these signals is of little interest to the casual reader of these pages, owners of WB 1400 receivers may be interested to see the Telecommunication Instruction E9 E3103 found in the Documentation Library on this website. See Section 4.5 & 4.6 on Pages 9 & 10
Terminating Unit WB1400 Gallery
Police Routine Functional Test
The police carried out a routine test of carrier receivers at 3 month intervals. The test was performed at 0900, 1500 and 2000 hours. At each of these times, a short test of both the 'Call' and 'Warning' signal and a spoken message using a codeword the receiver owner wrote on a test form they must return to the police war duties officer, was repeated a total of five times at one minute intervals.
Tunbridge Wells Carrier Control Point
I am most grateful for the feedback received from Nick Ashdown in March 2012 for an actual recording of a WB 1400 test broadcast. I have reproduced an extract from Nick's email below. I find it incredible that two people have been kind enough to send me recordings of the same CCP but made decades apart.
I was recently going through old cassette tapes and found the attached recording of a routine test from Tunbridge Wells CCP on our WB1400 recorded on the 29th of July 1987. I thought it would be a good comparison to the WB400 (we used to have one of these before it was swapped to the 1400) recording you have also from Tunbridge Wells.
Unfortunately my father died back in 1967, however we (My Mother) retained responsibility for the equipment and its routine checks up until it was removed in late 1987 (at our request). We also had a siren in its crate which we also tested once a year or so, not at full speed as we did not wish to alarm the villagers. I made the recording as we planned to ask for its removal and wanted to have something to remind us of the little box next to the phone by the front door. Very few people in the village new of its existence, when people visited, if they asked we just said ‘it’s something to do with the telephone.
Recording of a Routine Test Broadcast made 29/07/1987
[Confidence Tone] tick-tick-tick
[Select Signal] 8 rapid soft bleeps
[Call Signal] loud pips
This is the Tunbridge Wells Carrier Control Point making a routine test broadcast. You will now hear a short test Warning Signal.
. . . pause . . .
[Select Signal] 8 rapid soft bleeps
[Alarm Signal] wow-wow
Now please write the codeword Sunderland on your routine test report card.
Complete the remainder of the details and post.
Remember to switch off your loudspeaker, thank you.
. . . pause . . .
[Confidence Tone] tick-tick-tick
The WB400 for Comparison
This is a WB400 test broadcast also made by the Tunbridge Wells CCP. This recording was made circa 1966, 21 years before the one featured above. Note the wording is very similar.
A transcription of this message appears on the WB400 page. If you haven't already visited that page, afterwards, please use the website menu to visit the WB400 & 600 description.
Training Carrier Control Point Users
Two different kinds of training unit were made in very limited numbers. These were used for training police and BT Personnel in training schools, independently of the normal network, without the danger of setting off real sirens.
The version featured here, has a socket on the end of a flexible cable, into which a CCP console is plugged in. The training module can simulate incoming calls from the UKWMO Group HQ and a HANDEL message. As well as responding to siren signals and spoken messages.
Control Point Exchange WB1400 Era
In the block schematic, the Carrier Control Point CCP is connected via the three pairs of wires leaving the left hand side of the drawing. The thick double headed arrowed lines represent the external lines to the (CCP) located at the police station. The X and Y paths are routed in different cables for security against cable damage. Audio from the HANDEL interface goes towards the CCP. The CCP to group circuit is the third pair of wires shown.
The two speaking clock feeds and the private circuit to the ROC Group HQ enter the right hand side of the schematic. The carrier leaves the schematic at the bottom and feeds one or more distribution shelves, which send the carrier out on customers lines and onwards to other exchanges in the area.
Gavin Saxby has kindly supplied the photographs in this section. The Control Point Exchange (CPE) consists of one control shelf (Equipment Carrier WB 1401) and one or more distribution shelves (Equipment Carrier WB 1402). The CPE shelves are fitted in the steel cabinet previously used by the WB400 CPE. The cabinet is cabled back to a connection block on the telephone exchange's main distribution frame, where all the external circuits are connected.
Looking down from the top of the cabinet the CPE interface shelf is at the top and a distribution shelf below it. Each shelf holds a number of slide in units, each type of "Unit WB1400" is identified by a stroke number. To ensure the correct slide in unit is fitted in each position, its stroke number is engraved along the bottom of the shelf.
Each HANDEL interface (Unit WB 1400/1B) amplifies the audio from the speaking clock in the direction of the CCP. It detects a 1200Hz plus 1440Hz P+Q signal lasting for more than 1 second sent immediately before the Attack Warning message and converts it into a 180Hz signal of 711mS duration to alert the CCP. A filter blocks the carrier coming back from the CCP over the X and Y paths from the audio amplifier.
The carrier from the CCP is normally received along both the X and Y paths. A preamplifier (Unit WB 1400/2B) in each path monitors the carrier, if it fails, a signal is passed to the changeover unit (Unit WB 1400/7B). The changeover unit returns a signal selecting only one of the pair of pre-amplifiers to turn its output on. Should one path fail the other path is automatically selected. A manual changeover button is also provided for maintenance staff. The changeover unit raises an alarm should either or both carriers fail.
The two CCP power units extend a signal over the X and Y path to indicate their health. This too is monitored by the changeover unit and an appropriate alarm raised on failure. If both fail it is assumed the CCP is running on batteries, the duration is recorded on the resetable meter.
The line between the CCP and the UKWMO Group HQ is routed via a signalling converter (Unit WB 1400/10A) when Group calls the CCP, the balanced battery signal from Group is converted to 25Hz ringing towards the CCP. The CCP calls Group by placing an earth on its B-wire only, the converter sends balanced battery to call Group Headquarters. Whereas the HANDEL circuits are unidirectional, the line to the Group works bothways for speech and signalling.
The CPE shelf power is supplied by the Unit WB 1400/8B and is derived from the telephone exchange -50 volt supply with a 1000 hour reserve in the form of Lithium Chloride batteries in the box below.
Control Point Exchange Gallery
East Kilbride CCP and Receivers : A Working Example
The gallery contains a selection of the original record cards from East Kilbride, a town located on the south east side of Glasgow. The records represent only the Control Point Exchange (CPE) and the receiver points associated with that exchange only. There are carrier feeds to three nearby exchanges which have their own receiver points. I am most grateful to Mike Scott for this information that he gathered during the creation of the HANDEL display at the Dundee Sector Museum which utilises the old East Kilbride CPE rack.
Every Carrier Control Area ( CCA) has a three digit code number, East Kilbride CCA is 233. All receiver points bear this number followed by a slash identifying the individual feed. The letters EFI appear on a number of records, this is the internal code for East Kilbride Exchange. The whole of a Carrier Area is recorded as PW 103xxx, where xxx is that 3-digit code. East Kilbride is PW103233 but I don't have the whole CCA drawing, however further down the page in the "Carrier Distribution between Exchanges" topic is a drawing for the whole of the Swansea CCA, PW 103036. There is no information on Swansea's receiver points available.
The gallery images are explained below.
Google Earth view of Receiver Points, Red = Siren Receivers, Green = Speech Receivers, Orange = Both Siren and Speech Receivers served by East Kilbride exchange.
Google Earth view of Exchange (CPE), Firestation and Police Station with the CCP and Receiver point 233/1 having both speech and siren receivers.
The CPE Record Card A526(a) showing the incoming terminations from the CCP and the outgoing carrier paths to Rutherglen, Busby and Griffnock exchanges. The CCP has two feeds, the X and Y paths.
The reverse side of the A526 card showing the Distribution Amplifiers and Local Line Units used for each receiver point. In receiver point order.
The Station Record A741(a) showing the receiver point number, location and bearer used for carrier feed.
Reverse side of A471, showing more receiver points.
Equipment Provision A403(a) Same data as A526 above, but seen from the Distribution Amplifier point of view. 1 of 2
Equipment Provision A403(a) for another Distribution Amplifier shelf. 2 of 2
Fault Record Card A2699(a) recording faults seen from the perspective of speech receiver 233/90
Fault Record Card A2699(a) recording faults seen from the perspective of siren receiver 233/12
Fault Record Card A2699(a) recording faults seen from the perspective of 233/5, where there are both a speech receiver in the Stationery Store and siren receiver in the mains switch room, as the siren control panel has to be close to the incoming mains supply. At locations with a single phone line serving both receivers, then an arrangement described on the WB1400 Part 2 page in topic "Special Cases Preventing Fault Monitoring from the Local Exchange" will be needed.
CPE Records Gallery
Carrier Control Area
Considerable changes were made in the way the carrier was distributed when WB1400 replaced the old system. Only the feed from the Carrier Control Point (CCP) to the Control Point Exchange (CPE) remained duplicated. The CPE control shelf selects one supply for further distribution around the network.
Duplicated distribution feeds were considered unnecessary as by the nineteen eighties most small exchanges were fed by underground cable, therefore less prone to faults. If an exchange loses its carrier feed, an exchange fault alarm is raised, previously this was only detected when customer's local call charging failed.
Usually there are a chain of exchanges, each feeding the carrier to the next. New features were introduced so the loss of incoming carrier at one exchange didn't cause false alarms at exchanges further along the chain.
The Swansea Carrier Area comprised of Swansea Control Point Exchange (CPE) and 47 dependant distribution exchanges. The Purple coloured links in the enlarged diagram show the chain of carrier feeds radiating from Swansea CCP. In most cases the carrier is transferred between exchanges using phantom working over two pairs of wires. A description of phantom working is too technical for the scope of this page. Over the short distance between Mayals to Mumbles exchanges, only a single pair of wires was required.
On the six links shown in Blue in the enlarged diagram, the 72 kHz carrier could not be extended over the cable network as the losses were too high at carrier frequency so they are sent as audio instead. At the feeding exchange, the carrier is demodulated to audio by a Unit WB 1400/6A. At the receiving exchange the normal carrier Pre-Amplifier (Unit WB 1400/2B) is replaced by a Local Oscillator / Modulator (Unit WB 1400/3A). The incoming audio modulates a locally generated 72 kHz carrier for distribution to its own customers and in the case of Llandeilo to feed the carrier forward to Dryslwyn, Talley and Llangadog exchanges, for further onward distribution.
To safeguard against the failure of the audio feed circuit, the /3A unit, monitors the 'G' tone sent every six hours by the CCP as part of the siren receiver test signal. If this is not received after 24 hours, an exchange prompt alarm is raised to alert maintenance staff.
These photographs (taken at the Avoncroft Museum, Bromsgrove 15/07/04) show how the Equipment Carrier WB400A and Box Battery WB400A, formerly used for the WB400 system were modified to house the WB1400 distribution equipment. The cabinet is part of the exhibit of small rural dependent exchange 'UAX13' at the museum.
The main cabinet is 1'-10½" wide, 1'-0½" deep, its height above battery box 2'-8". The
Battery Box is 1'-10½" wide, 1'-2" deep, 1'-11" high. Both are made of heavy gauge steel and are connected to the Main Distribution Frame via a conduit to protect the cables.
Removing the screws and lifting off the front cover reveals an Equipment Carrier WB1402, Diag. WB29604; Consisting of a shelf of slide in units which may be dropped forward to give access to the cards. In the enlarged view a strip along the bottom of the shelf indicates where the units fit. For example 4B is a Unit WB 1400/4B
The incoming carrier signal from the previous exchange enters the shelf via the Filter Unit which sends the signal to the pre-amplifier (Unit WB 1400/2B) Its output is connected to the inputs of up to three Distribution units (Unit WB 1400/4B). Each distribution unit further amplifies the carrier and provides 5 isolated outputs. The actual number of units fitted depends on the demand. Any of the 15 possible outputs can either be connected to outgoing junctions to feed dependent exchanges or used to supply warning point customers lines.
According to demand, the shelf can be fitted with a maximum of five Local Line Units (Unit WB 1400/5A). Each card will supply up to two customers lines, either with the trickle charge for the Speech Receiver battery or to monitor the confirmation signal returned from the Siren Signalling Receiver in response to the automatic test signal sent by the CCP. Should the trickle charge fail (Line broken) or the confirmation signal not be returned from a siren control unit, a telephone exchange maintenance alarm is raised.
Power for the distribution shelf is normally obtained from the telephone exchange 50 volt supply. Should this fail the reserve battery is brought into use by the shelf Power Unit and Alarm Interface (Unit WB 1400/8B). Exchange fault alarms are raised through this interface should the incoming carrier fail or one of the local lines monitored by the /5A fail.
The reserve batteries and their Terminating Unit WB1403 are held in the battery box underneath the cabinet. One battery Dry No. 100, is fitted for each Carrier Distribution Unit /4B on the shelf.
In lightly populated areas and islands, telephone exchanges may be served by radio links in the UHF or microwave range instead of copper pairs in overhead wires or underground cables. It is not possible send the WB1400 carrier over radio circuits or on very long lengths of underground cables.
To overcome this problem, the serving exchange's shelf is fitted with a Audio Feeder (Unit WB 1400/6A) in place of the fifth Local Line unit /5A. This produces two audio outputs suitable for transmission over long cable routes or radio circuits.
At the dependent exchange, the normal carrier Pre-Amplifier (Unit WB 1400/2B) is replaced by a Local Oscillator / Modulator (Unit WB 1400/3A) which modulates a locally generated 72kHz carrier with the incoming audio signal which is distributed as normal by the rest of the shelf.
A few customers may be connected to their exchange by a long cable route unsuitable for transmission of the usual carrier. By special arrangement with BT Factories Division, carrier receivers would be modified by them to work with an audio input rather than carrier. After modification, they were designated as Receiver Speech WB1402 or WB1403 (in place of WB1400 or 1401 respectively) and Receiver Signalling WB1402 or WB1403 (in place of WB1400 or WB1401). These customers would be fed from the audio output from the /6A slide in unit.
Distribution Shelf Gallery
Standby Power at Carrier Exchanges
UK telephone exchange apparatus is powered from a battery backed 50 volt supply derived from the mains supply. In larger exchanges, diesel generators provide a back up against a mains supply failure.
The 50 volt DC feed to the automatic telephone switching apparatus is supplied by a rectifier, or in larger exchanges a number of rectifier modules, with one or more batteries connected in parallel across the exchange load. These are kept charged by the rectifier modules. Should the mains fail, the batteries continue to run the exchange for a considerable period of time or until the generator, if provided, automatically starts. During the cold war period, sufficient diesel was stored to keep the generator(s) running for 28 days without replenishment.
During the cold war period, the small rural exchanges, Unit Automatic Exchanges (UAX) with 400 or fewer lines, did not have a standby generator. Due to their light load they could keep running for a number of days without mains power. In a post attack situation it is likely their exchange battery could fully discharge.
WB1400 Reserve Batteries
Each WB1400 cabinet has its own set of reserve batteries to guard against loss of the 50 volt DC exchange battery supply, due to the exchange battery completely discharging if the mains fails and the standby generator fails to start or breaks down. Unlike the rechargeable exchange lead-acid battery, the reserve batteries use lithium chloride technology which is not rechargeable. The reserve battery capacity is designed to last for 1000 hours.
At the Control Point Exchange (CPE) there will be at least two shelves, a CPE shelf and a distribution shelf. The CPE shelf is supplied from three batteries plugged into a Terminating Unit WB 1403. The distribution shelf has a separate set of batteries.
According to the number of outputs required there may be more than one distribution shelf at a CPE or at intermediate / distribution exchanges. Each shelf has its own separate battery backup with a separate Terminating Unit WB 1403 fitted with one battery per distribution amplifier (Unit WB 1400/4B) on the shelf. There will be at least one, with a maximum of three amplifiers per shelf and hence a maximum of three batteries in parallel per terminating unit. The reserve batteries only supply enough power to operate the carrier distribution function but not the trickle charge for the speech receivers, these rely on their own internal rechargeable battery to keep functioning.
Each Lithium battery measures 13 cm x 13 cm and 6 cm deep, known by B.T. as a Battery Dry No. 100, its rated as 12 volt 20 Ampere Hours. The Terminating Unit WB 1403 has three battery connectors and an electro-chemical elapsed time indicator (Indicator WB 1400) scaled in 0-1000 hours. These items are featured in the photo gallery.