1947: Reläställverk till SJ från amerikanska Union Switch?

    US&S Relay Interlockings for the swedish state railways?

1947 skrevs nedanstående brev adresserat till den amerikanska leverantören Union Switch. Det finns dock en påteckning Ej gått på brevkopian i SJ-arkivet, så man kan antaga att brevet av någon anledning aldrig gick iväg. Detta kan förstås kollas mot diariet.
Dokumenten är OCR-tolkade, varför en del text kan ha förvanskats. Beskrivningen av dvärgsignalbilderna har vid tolkningen  huvudsakligen fallit bort, men torde vara välkänd för svenska läsare.  Materialet finns i volym Ebrsi EI:21 i riksarkivet. De enda dokument som finns utöver det som återges nedan är svenska versioner av breven. Ritningar och foton saknas.

Until the early 1950s, all relay interlockings for the swedish state railways were procured from the signalling branch of the swedish telecom manufacturer Ericsson.  Lack of manufacturing capacity in Sweden (and probably other factors too) obviously made the state railways consider buying interlockings from Union Switch.  The letter to US&S reproduced below may however never have left the state railway headquarters, and the solution eventually chosen by the railway administration was to build its own interlockings, with relays,  illuminated diagrams and other components from Ericsson and other swedish manufacturers. The Stockholm metro however started buying interlockings and cab signalling from US&S about the same time as the state railways were thinking of importing from the US. 

The text below is processed by OCR from  documents in the archive of the swedish state railway administration.  The representation of the position-light dwarf signal indictions have regrettably got lost in the OCR recognition.  

The term Depending on the lines probably has to do with traffic locking. Traffic control systems with bi-directional working have been common in Sweden since the 1930s.


Stockholm, April 1st, 1947.
The Union Switch & Signal Company, Swissvale 18, Pa.

Dear Sirs,
Since the early days of the railway construction the Swedish Government Railways have formed the spine of the communication system in Sweden, and in recent years they have been further extended through the incorporation of a great number of railroads previously privatly owned. As some of them have been defectively equipped and as at the same time the traffic has been enlarging generally, the requirements of material have highly increased, especially in the signalling field. As a matter of fact these requirements are so great that they are not likely to be procured only by our home industry, which has supplied us the greater part of signalling materials in recent years.

We are therefore very interested in trying to bring about an import of such material. By this means we should get an opportunity of benefitting directly by experiences derived abroad, an advantage of greatest importance for the moment, when the principles for the future shape of our railway signalling system are being taken into consideration.

In pursuance of the above mentioned we apply to you inquiring, if in the immediate future you should be interested in delivering interlocking machines for some 10 yards. Malmslätt, a station situated on the line Stockholm-Malmö, is typical for these railway-yards. We enclose a plane drawing, Ebr 68-29, a locking sheet 62-146 and a special description concerning this station.

We should greatly appreciate an opportunity of trying modern interlocking machines with the levers arranged in the illuminated track diagram and for instance with relays of plug-in type, now in use in U.S.A. As to the rest the excecution ought to accomodate itself to Swedish principles.

Elektroteknlska byrån
Ebr 60-29/47.

Malmslätt. Description of Planned Electric Interlocking Replacing an Old Mechanical Interlocking.

Hereto drawing Ebr 68-29 and locking sheet 62-146.

The station is situated on the double track line Linköping-Mjölby, a part of the main line Stockholm-Malmö, between Linköping (north) and Vikingstad (south). The line is electrified with single phase a.c. 16000 volt 16 2/3 cycles.

The line is normally trafficked with left hand driving. Automatic block is to be arranged in connection with the installation of the new interlocking plant. The line is also to be arranged for right hand driving and dwarf signals are therefore used e.g. 11 and 12. For left hand driving three aspect search-light signals are used e.g. 1 and 2.

Most trains pass the station without stop, on  the main tracks III and IV. Passenger trains with stop on the station also traffic these tracks. Track II is trafficked by local freight trains and some passenger trains.

Every day the station is passed by 18 express trains 20 passenger trains, 14 through freight trains and 2 local freight trains.


The switches 2/17, 4/15, 6/13, 12/5, 14/3 and 16/1 are to be operated with electric switch machines governed by the interlocking machine in the station and by  local levers close to the switches. The switches are electrically coupled in pair, e.g. switches 2 and 17, 4 and 15 etc coupled so that they have one lever and SS indication. Local operation of the switches can naturally take place only when they are not locked. Furthermore a separate lever on the interlocking machineshall be moved. When doing this, a lamp at the local lever lights up. Switch 8, derail SpII, switch 7 and derail SpIII are only locally operated with stands, but are to be electrically locked from the interlocking machine.

Track circuits.

All routes are provided with track circuits. A track circuit which contains switches is named by these. A. track circuit Which contains switches 4 and 17 is named S 4/l7. The track circuit of track IV is named SIV. The line out of the station is provided with track circuits.    One rail in the track circuits is not broken. It is not proposed to arrange impedance bonds now. The track circuits are to be feeded with a.c. 100 cycles, which system is to be used for the line block.

Home signals.

All signals except B and E stand to the left of the track. The entrance signals A l/2, P l/2 and the exit signals C IV, D III are signals for left band driving and are light signals with many aspects. Signals A l/2 and F l/2 have 4 lights and show 1 steady red light for stop, 1 steady green + 1 flashing green for entrance to main track, when the exit signal shows stop. If the exit signal shows proceed, the entrance signal shows 1 steady green light + 1 white flashing light. If the route is to track II, the entrance signal shows 2 steady green lights.

Dwarf signals.

At the ends of the station tracks dwarf signals are placed, and the normal position is oo. When the route is clear, the aspect is  :    The dwarf signals CII, CIII, DII and DIV have below the uncoloured lights two green lights which show signal to the line track which is the route. E.g. shows CIII   : uncoloured, when the train goes towards signal 2. If the route is towards signal 12, the aspect 0   uncoloured is o    green     The dwarf signals CIV and DIII are strenghtened by main signals CIV and DIII by train movements, and therefore these signals are not provided with green aspects

By shunting movements the dwarfs show "shunting permitted" , and at the same time the switches are released for local operation. The dwarfs then show o .If possible, more than one signal shows "shunting permitted". E.g. the dwarfs CIII and CII show "shunting permitted" at the same time as the switches 12/5 are released for local operation by shunting between tracks II and III.


The routes are marked with small letters e.g. eIV, fl, aII, bIV, cII2, cIII2, cIV2. eIV means route from signal E to track IV. f means route from signal F to track IV. cII2
means route from signal cII to signal 2.

Route eIV and fI reach to signal cIV. Routes cIV and 12 cIV reach to signal 2 resp. 12,when a route is clear, the switches shall be locked and other routes which are dependent shall be blocked up. The route shall be locked, until the train has passed the last switch in it. Naturally the signals shall be dependent on track circuits in the route.

Distant signals.

Before the home signal is a distant signal showing green flashing light, when the home signal aspect is "stop", white flashing light, when the home signal aspect is "proceed on main route" and green flashing light + yellow steady light, when the home signal aspect is "take siding" (two, first siding or three, another siding steady green lights).

Locking sheet

The locking sheet is shown on Ebr 62-146.  It is so arranged that longest to the left is shown from where the train comes and where it shall go. So e.g.   one can come frome Linköping on the left track to tracks IT,  III or IV. Those routes are marked aII, aIII resp. alV. Columns A l/2, B, CII, CIII, CIV, DII etc, mean the signals.

When signal A l/2 is operated for route aII, all signalling for aIII, aIV, bII, bIII is blocked by different 12 position of the switches. For routes CII  , eII, eIII, fII and fIII different switch positions are not blocked, but the signals may not be operated at the same time as aII. For this separate dependences must be arranged.

Routes bIV, cIV2, dll1, dll11 etc. have no + in the column and can therefore be operated at the same time as all.

How many green lights there are in the signals and the position of the dwarf signals is shown in the column for signal aspects. Mark that the lower lights on the dwarfs with 6 lights are green.

The columns next to right show which switches are to be locked and in which position.

For route aII the central-operated switches l/l6, 3/l4, are locked in + or normal position and switches 5/12 in - or reverse position. The local-operated but electrically interlocked switches and derails 8/SpI,/SpII and 7/SpIII are locked in normal position.

Then there is shown which track circuits must be free for getting proceed aspect. Hence the signal aspect for aII is dependent on track circuits 1/5/14, S12. and SII.

Unguarded driving.

Because many trains in succesion pass the station or only make a short stand without shunting movements, a central lock K 14 (King lever) is used. When it is locked, the automatic route releasers do not work, and therefore the signals go back to proceed aspect, when the route is free from trains. The stations form a block. Unguarded driving can only be arranged for left hand driving. The lowest line shows the lockings in that case.

As a complement to the lockings for the routes, there is shown by which signals (routes) every switch lever (switch pair) is locked. Lever 1/16 is locked by all, aIII, alV, bll, 2    12 bIll, blV, cll , cII. Moreover operation of switches 1/16 is blocked by track circuits 1/5/4 and 3/16.

Emergency release.

If a route is cleared, and the signals show clear aspect, but the train does not go over the route, time releaser (mechanical or termic) is used,

Depending on the lines.

Chosing of drive direction (left or right hand) on the lines is made with levers, not shown on the plan. Departure (exit) signal from the station to any line cannot be shown, less the line is free e.g. line signal 1, 11, 2 or 12 shows proceed which is depending on the chose of drive-direction and the line track circuits.


To explane  our cable arrangements we enclose diagram Bbr 68-10 showing Stehag also situated on the line Stockholm-Malmo near Malmo. It is  of the same size as Malmslatt. The signal indications are not the same as Malmslatt but principally the same.

A cable 56 x 1 means  56 wires of 1 mm2 area cable 37 x 1 + 2 x 0,4 means 37 wires of 1 and 2 wires of 0,4 mm . The latter are used for telephone within the station. Wires to switch machines are placed in separate cables. Signals and track circuits often have cables in common. For control of   track circuits on the line we use wires in the distance telephone cables, not shown on this plan.

A typical diagram of track circuits is Ebr 68-17. As earlier named, the one rail is unbroken to permit the locomotive current to go back.

Illuminated track diagram for Stehag is shown on Ebr 68-11. All indications are shown on the track diagram. With lamps there is thus shown the track circuits,  signal aspects, position of the switches, routes etc.

In order to furthermore show our standard, designing and apparatus we enclose some leaves from a handbook for signal maintainers.

1.    Electric switch machine, mechanical parts.  One throw rod and one control rod are connected to every switch tongue. The point lying against the rail is locked by the point lying from the rail. The switch is kept in position by aid of a friction clutch on the motor shaft. The machine is provided with contacts for the motor circuit and for SS indication.

2.    Shows a typical circuit of a switch machine with series motor. The motor is short-circuited in the end position of the lever. The levers are of Westinghouses princip with indication and end position. For local operation a lever is arranged by the switch. A back contact of the L-relay supersedes the track relay by local operation.

3.    Shows another manner to demonstrate the connection between lever and switch machine.

4.    Shows a station with electric interlocking and interlocking machine with turn levers.  The lever operation is made in the manner as on Westinghouse's interlocking machines. The signals are marked h and v, which means that the signal is operated by right-turning or left-turning of the signal lever respectively.

5-7.    locking sheet which is arranged in the same manner as that of Westinghouse'    with the difference that in the last column stands "if not" instead of Westinghouse's  "when". Underwritten numbers  (2) mean reverse position. Without underwriting means  (2) normal position. A ring round the number    (2)    means normal or reverse position.

8-12.    These diagrams are drawned in about the same manner as those of the Westinghouse Co. Leave 8 shows home signal relays and point-locking, 9 shows H-relay, D-relay and relay circuits used for showing "shunting permitted" on the dwarfs ,| when the switches are to he locally operated. 10 shows I-relays that operate signals in the other end of the track showing stop in a direction opposite to that for which the route is clear. These signals are used for informing personal in the station yard that a train is coming on that track. Furthermore a circuit for releasing a clear route is given. At last the release circuit for locking magnet by clear shunting route is shown. 11 shows typical circuits on dwarf signals. Instead of resistances for the indication lamps on the illumnated track diagram current transformers are now used. 12 shows typical circuits of home light signals and distant signals. The circuits for a home signal are arranged in such a way that if a green lamp breaks, other eventually burning green lamps will he extinguished. In series with the green lamps there is a light relay which is energized, when green aspect is shown, and short-circuits the feeding transformer for the red light. In the circuit for the red light is no contact.


  1.  Electric switch machine
  2. cable distributors
  3. Dwarf signal
  4. Home signal with 5 lights and dwarf signal with 4 lights
  5. Distant signal with siding light
  6. Electric lock in connection to switch stand
  7. "  "    "     "   "    "  with cover
  8. open Relay boxes
  9. Electric interlocking machine with illuminated track diagram

Stockholm, March 14th,  1947.
Elektrotekniska byrån.




Sidan uppdaterad den 8 december 2005