Key takeaways
- The Class 643 is a diesel locomotive from the American-influenced procurement line of the Yugoslav era.
- Quickest way to identify it: no pantograph, exhaust on the roof, class number beginning with 6.
- The 6xx block is the system: at SŽ, numbers starting with 6 stand for diesel locomotives.
- Diesel locomotives work where the overhead line is missing or gets in the way – on sidings, on shunting duties and on non-electrified lines.
- Fleet and deployment change; older diesel locomotives are gradually being replaced by newer vehicles.
Contents
Fact file
| Vehicle type | Diesel locomotive for shunting and light line duties |
|---|---|
| Design origin | American design lineage from General Motors / EMD, procured and built in Yugoslavia |
| Traction | Diesel engine, independent of the overhead line |
| Class number | 643 in the numerical class system of Slovenske železnice |
| Numbering logic | At SŽ, the 6xx block stands for diesel locomotives |
| UIC country code Slovenia | 79 |
Identifying features
Is this really the class in front of you?
- No pantograph, but an exhaust and radiator section instead – clearly a diesel locomotive
- Class number begins with 643; at SŽ the 6xx block denotes diesel traction
- Design in the American tradition with a separate cab and a long engine compartment
- Typically seen on station and trip working rather than at the head of fast passenger trains
- Can also work under the wires, because its traction is independent of the network
- Liveries follow whichever SŽ colour schemes apply and have changed over the years
Updated: August 2026 – No pantograph, but an exhaust and engine noise instead: the Class 643 is one of the diesel work vehicles of Slovenske železnice. It does not haul prestige trains; it moves wagons, runs trip workings and works where the overhead line ends. This page shows how to place it, what the Slovenian numbering system reveals and what to look out for when sighting and photographing it.
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What is the Class 643?
The SŽ Class 643 is a diesel locomotive for shunting and light line duties on the Slovenian network. Its design lineage goes back to the American design tradition of General Motors and its locomotive division EMD, which strongly shaped the diesel fleet in the Yugoslav era.
Operationally, that puts it firmly in its place: it is not a vehicle for fast passenger trains but one for work behind the scenes. Moving wagons, preparing trains, running trip workings between stations, serving private sidings – that is the field of work for this class of vehicle, in Slovenia just as in Germany.
The Slovenian numbering system: what the first digit reveals
Slovenia does without type letters and works with number blocks instead. That makes placing a vehicle surprisingly easy once you know the scheme – often the first digit is enough for a rough assignment.
| Number range | Vehicle type | What you see on the vehicle |
|---|---|---|
| 3xx | Electric traction units | Pantograph on the roof, no exhaust |
| 6xx | Diesel locomotives and diesel multiple units | Exhaust and radiator section, no pantograph |
| 7xx | Diesel railcars | Multi-car or single-car unit without a separate locomotive |
| Manufacturer number | Modern interoperable locomotives | European type numbers such as 193 or 541 |
The difference from the German system is small, but from the Norwegian one it is large: Norway names types with letters such as El, Di or Skd, Slovenia with numbers. Both systems are logical, but if you mix them up, you look in the wrong place. The general approach to identifying unknown vehicles is described in the guide to identifying classes – it works regardless of the country.
Look at the roof
No pantograph, but an exhaust and radiator grilles: that settles the matter before you have read any number.
Read the first digit
If the class number begins with a 6, you are in SŽ's diesel range. A 3 at the start points to electric traction units.
Place the body design
A separate cab with a long engine compartment points to the American-influenced design line that defined the Yugoslav diesel fleet.
Watch what it is doing
Moving wagons, coupling, short runs back and forth: this pattern belongs to shunting, not to line services.
What a diesel locomotive does in Slovenian operations
The network of Slovenske železnice is largely electrified – but not everywhere and not on every track. That is exactly where the role of diesel traction comes from. It fills the gaps left by the overhead line and takes on tasks for which electric traction would be impractical.
| Task | Typical setting | Observability |
|---|---|---|
| Shunting in the station | Track groups away from the platforms, loading roads | medium, often from a distance |
| Trip workings | Short distances between stations and sidings | variable, as required |
| Serving non-electrified lines | Branch lines away from the main routes | easier to plan if a timetable exists |
| Engineering and works trains | Engineering works, line closures | irregular, but often in unusual places |
| Pilot and stand-in duties | Wherever power is lacking at short notice | rare, hardly predictable |
By comparison, vehicles such as the Class 661 and the Class 664 are designed for heavier line duties, while diesel railcars such as the Class 711 cover passenger services on non-electrified lines. Together they form a picture familiar from Germany – just with different numbers and a different procurement history.
Fleet and deployment change
Which diesel locomotives are still in service and what for shifts with new procurements, inspection deadlines and timetable years. Older information from the internet goes out of date particularly quickly for this class of vehicle – check the current situation before a targeted trip.
See what is being reported in Slovenia right now
For shunting and trip workings, current community sightings are often the only usable source.
Spotting and photography: diesel locomotives call for patience
Photographing a shunting locomotive works differently from photographing a long-distance train. There is no timetable you can rely on, and the interesting areas are almost always inaccessible. That sounds discouraging, but it can be solved – with the right approach.
Find a spot at the end of the platform
The end of the platform is usually the last publicly accessible point with a view of the working tracks. You may not go any further: beyond it, the operational railway land begins.
Plan for more focal length
Because you have to keep your distance, you need more telephoto than for a normal platform shot. Build in reserve instead of cropping at the end.
Anticipate the movement
Shunting moves are slow and repeat themselves. Watch one round first, then you will know where the vehicle is about to reappear – and can prepare your framing.
Secure the number separately
Alongside the picture, take a second, tighter photo of just the vehicle markings. Without a legible number, a sighting is only half the job as documentation.
One more note on expectations: shunting locomotives are not vehicles you tick off and never need again. Because they work in the same place for years, repeat visits pay off – different light, a different season and a different activity produce completely different pictures of the same vehicle. If you really want to document a class, think in series rather than single shots.
How to observe shunting areas systematically and legally is described in the guide to spotting at the marshalling yard. Because boundaries are crossed quickly there, the article on safe distance from the track is essential reading too: track areas, stabling sidings and depots are operational railway land and not a photo spot – in Slovenia no more than in Germany.
Common mix-ups
It points to a diesel locomotive of the 6xx classes if …
- there is no pantograph, but an exhaust and radiator section instead
- the class number begins with a 6
- the vehicle is working on shunting or trip duties
- it is running on a non-electrified track
Take a closer look if …
- several diesel locomotives of different classes stand side by side and their designs look similar
- the markings are partly covered or weathered
- the vehicle is stabled and you cannot observe any activity
It is not a diesel locomotive if …
- a pantograph is raised to the overhead line
- the class number begins with 3, 193 or 541
- it is a continuous multiple unit without a separate locomotive
Verdict
The Class 643 is not a vehicle for glossy pictures but one for people who want to understand how the railway works. It shows how Slovenia built up its diesel fleet, what diesel traction is still needed for on a largely electrified network and how logically the Slovenian numbering system works. It can be identified in two steps – look at the roof, read the first digit. Everything else is detail work.
In short
No pantograph, number beginning with 6, work in the station rather than on the main line: that is the signature of Slovenian diesel traction. The Class 643 is part of it – and its workings depend on demand, so they can only be planned with patience and current information.
Document sightings abroad properly
Number, location, date and activity in one place – that is how individual photos become a reliable collection.
Summary
- The SŽ Class 643 is one of the diesel work vehicles of the Slovenian network and comes from Yugoslavia's American-influenced procurement tradition.
- The Slovenian class system arranges vehicles by number blocks – diesel locomotives sit in the 6xx range.
- Because diesel locomotives work on shunting and trip duties, their workings are harder to plan for than those of multiple units.
- The class does not run in Germany; it can only be documented on site or through archive material.
Frequently asked questions
What is the SŽ Class 643?
A diesel locomotive of the Slovenian network that comes from the American-influenced procurement line of the Yugoslav state railway. Vehicles of this size are typically used for shunting, trip workings and light line duties. The class number 643 clearly assigns it to diesel traction in the Slovenian system.
Why do Slovenian diesel locomotives begin with a 6?
Because the Slovenian class system works with number blocks instead of letters. Electric traction units sit in the 3xx range, diesel locomotives in the 6xx range, diesel railcars in the 7xx range. If you know this structure, you can often place a vehicle before you can make out any details – the first digit carries the information.
How do I tell a diesel locomotive from an electric locomotive?
By the roof. An electric locomotive carries at least one pantograph; a diesel locomotive has an exhaust and radiator structures instead. This feature works from a great distance and in poor light too – which is why it is always the first thing to check before you deal with the shape of the front or the number.
Why do diesel locomotives also run under the wires?
Because their traction is independent of the network and therefore works everywhere. On shunting duties that is a real advantage: depot tracks, loading roads and private sidings are often not electrified throughout, or the overhead line is switched off. A diesel locomotive can work regardless.
Does the Class 643 also run in Germany?
No. It was procured for Slovenian operations and is neither approved nor intended for regular service in Germany. For German spotters it is therefore purely a foreign vehicle – you can only see it on site, and only those who take down the number, date and location can document it.
Where is it worth looking for Slovenian diesel locomotives?
At larger stations with freight traffic, at junctions for non-electrified lines and around depots. Because shunting and trip workings run as required, there is no reliable timetable information – patience and a fallback subject are part of the planning.
Is the Class 643 still in service?
Older diesel locomotives in Slovenia, as everywhere, are being replaced gradually, and the status of individual machines differs. No reliable statement about the current fleet can be made here. So check the situation shortly before your trip using current sightings rather than older overviews from the internet.
What goes into a good sighting note?
The full vehicle number including the country code, plus date, location and the kind of activity observed. With shunting locomotives in particular, the activity is a piece of information in its own right: whether a locomotive is moving wagons, running a trip working or stabled says more about operations later than a bare list of numbers.
Log your sighting of the SZ Class 643
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