The Nomenclature System of Locomotives on IR

by Shirish Paranjape, 2000

Note: This article originally appeared in 'Indian Railways', Dec. 2000. It is reproduced here by generous permission of the author, Shirish Paranjape. Readers may also be interested in the FAQ pages on locomotives.

All travellers and enthusiasts would have observed, during their journeys, the alphanumeric numbers, such as 'WAP-4', 'WAG-7' boldly painted on the body of the locomotives operating on the Indian Railways. This article attempts to explain the system for nomenclature adopted by the Indian Railways for the locomotives operating on the Indian Railways.

The numbering system of locomotives comprises two parts. First, the code prefix such as 'WDM-2' or 'WAM-4' which denotes the type/class of the loco; and second, a serial number such as '17604'. Each letter in the code-prefix has a specific significance, and the understanding of this would help us in the overall understanding of the nomenclature adopted on IR, as well as the varied types of locomotives running on the IR.

The first (left-most) letter denotes the gauge. Thus, 'W' stands for Broad Gauge, 'Y' is Metre Gauge and 'Z' is Narrow Gauge. We will normally see one of these letters as the first letter in the number of the loco.

The Steam Saga

In the bygone era, life was simple, because there was only one category of loco, based on the fuel is used. Those were days of the elegant, huffing and puffing steam locos, also colloquially called 'coal engines'. In those days, on the broad gauge, we had:

  • 'WP' class locos, with a hemispherical front, which gave the loco a very majestic and powerful look.
  • 'WG' class locos, which had a flat front.

The letters 'P' and 'G' indicated Passenger service and Goods service, respectively. Which means that 'WP' was a broad gauge passenger service loco, while 'WG' was a broad gauge goods service loco. Due to the shift to diesel and electric traction, both these types of locos are no longer in service on IR, and can be seen only in museums.

On the metre gauge, we had the omnipresent 'YP' class locos, which, unlike their broad-gauge counterparts (WP), had a flat front. The goods trains on the metre gauge were pulled by 'YG' class locos, which had a look similar to the 'YP' locos.

Thus, in the days of steam traction, the second letter indicated the 'service class' of the loco, and mainly the 'WP'. 'WG', 'YP' & 'YG' class of steam locos dominated the IR scene.

The Change from Solid to Liquid Fuel

Then, in the sixties, came diesel traction, and life became a little more difficult. Most of the diesel locos operating on broad gauge are 'WDM-2' series, where 'W' is Broad Gauge, 'D' is Diesel, and 'M' is 'Mixed' (service). These versatile locos, made in India at DLW, Varanasi under license from ALCO, USA, have put in an exceedingly meritorious and long service in hauling passenger as well as goods trains, both singly and in pairs.

The number '2' indicates that it is a second generation loco, from design technology point of view. Its predecessor 'WDM-1' was used in much smaller numbers and were last seen on the Durg-Nagpur section of South Eastern Railway, hauling goods trains. The peculiarity of the WDM-1 was that it had the driver's cab only on one end, while the other end was flat -- like the ends of passenger coaches. So, while it appeared flush with the load behind it, the WDM- 1 had to be reversed for the journey in the opposite direction. On the other hand, 'WDM-2', though unsymmetrical, can be used in any direction without the need of reversing, thanks to the design of its driver's cab.

WDM-2's cousin on the metre gauge is an equally versatile 'YDM-4', while that on the narrow gauge is ZDM-1. You will also find 'WDS-4' bringing passenger trains into platform at the starting stations. ('S' indicates 'shunting class'). There are other variants such as 'WDP-1' ('P' for 'passenger service', and higher-powered (3100hp), 'WDP-2' and 'WDG-2' locos for passenger and goods service respectively.

While 'WDM-2' and its related variants are based on ALCO designs, IR has recently gone in for a new technology, powerful (4000hp) locos based on the designs of General Motors, USA. These locos are christened 'WDG-4' ('G' for Goods), and these are manufactured at DLW. These locos can be seen operating on the Hubli Division of the South Central Railway, hauling goods trains carrying bulk ore.

On the narrow gauge, locos such as 'ZDM' operate on Kangra Valley Railway and Kalka-Shimla Railway, while other narrow gauge variants pull tourist trains on the Neral-Matheran Railway near Mumbai.

The Electric Locomotives

The advent and the progress of Electric Traction has further complicated the numbering system. From a simple 'WP' or 'WG', we now move on to more complex nomenclatures such as 'WCAM-3', an addition of as many as 3 characters. But this addition is not without adequate meaning, as we will realise after the following discussion.

Electricity comes in two forms -- AC (Alternating Current) and DC (Direct Current). On Indian Railways, the Mumbai-Pune, Mumbai-Igatpuri and Mumbai-Virar sections are fed by DC supply (1,500V DC), while all other sections are fed by AC supply (25,000V AC). Therefore, the nomenclature system for electric locos includes a letter to differentiate between locos with DC traction from those with AC traction. As per this system, 'A' indicates 'AC traction' while 'C' indicates 'DC traction (not 'D', so as to avoid any confusion with diesel). One can, therefore, find 'WCG' class locos (Broad Gauge, DC traction, Goods duty) operating on the Mumbai Division, while their counterparts 'WAG' locos haul broad gauge goods trains on AC traction elsewhere on LR. Similarly, trains, such as Mumbai-Pune Deccan Queen Express were, till recently, hauled by gigantic 'WCM-l' and 'WCM-5' ('M' for 'Mixed' service, just as in 'WDM-2'), while Mail/Express trains in the other parts of the country are powered by AC electric locos such as 'WAM-4' (Broad Gauge, AC Traction, Mixed service).

The WAM-4 Ioco has been produced in very large numbers (upward of 500), and is in service very widely in India. Its predecessor WAM-1/2/3 can be seen operating on Eastern Railway, for instance, on Sealdah Division. 'WAG-2' is of Hitachi design and operates mainly on the Bhusawal Division of Central Railway. This is a very handsome-looking loco, which is also the case with its 'younger brother', the 'YAM-1' used for hauling trains on the only electrified metre gauge section on IR namely the Chennai-Chengalpattu section. Under Project Umgauge being implemented by the railways, this section will get converted to broad gauge, and rail enthusiasts will surely miss the sight of this lovely loco hauling a load of metre gauge coaches.

What WAM-4 is to Mail/Express trains, 'WAG-5' is to goods trains operating on the broad gauge. The WAG-S is the most common loco for hauling BG freight trains on AC traction. More than 700 locos of this variety can be seen on LR.

Driven by the ever-growing need for more speed & power, we have seen technological advancements on the IR scene too. Thus we now can commonly see a huge, 5000 horsepower, red-coloured, and well-contoured loco, the 'WAP-4' hauling super-fast Mail pr Express trains of as many as 24 coaches in various parts of the country. This BG-AC Passenger Service loco is capable of achieving speeds upto 140 kilometres per hour. Its predecessors, the 'WAP-l' and 'WAP-3' can be found in much lesser numbers -- they were probably used to improve the designs, which has now been adopted on the 'WAP4'

Modern Technology

The conventional locos had:

  • DC motors fed by DC overhead supply, such as for WCM, WCG locos (Electric locos, DC traction)
  • AC overhead supply, stepped down through a multi-winding transformer, rectified by static rectifiers, whose output was fed to the DC motors. Locos such as WAM, WAP, WAG are equipped with this technology. (Electric locos, AC traction).
  • Diesel fuel driving an engine, which operates an alternator, whose AC Electric output was rectified and fed to the DC motors, in locos such as WDM-2, WDP, WDG. Due to this the diesel locos are actually 'diesel-electric locos. These locos were actually with an on-board moving powerhouse operated on diesel fuel.

The latest technological innovation in traction is the use of 3-phase AC motors instead of DC motors as the prime movers in the loco. With a desire to implement this technology, IR purchased, under a transfer of technology agreement, two new types of electric locos from ADtranz. These locos, one with 6000hp, 160km/h (upgradable to 200km/h), and the other with 6000hp, 100km/h capability, are christened as WAP-5 and WAG-9 on the Indian Railways. These can be seen operating on the Northern and Eastern Railways hauling maillexpress and goods trains respectively.

The technology of AC motors as pnme movers applied to diesel traction is also now available with the IR. in the form of the WDG-4 loco, being produced at DLW under another technology transfer agreement (with General Motors, USA). This 4000hp, 160km/h loco will be found in increasing numbers as the production gradually increases.

While on one side this technology transfer was under progress, IR, through Chittaranjan Locomotive Works and RDSO, have in parallell developed an indigenous, powerful 5000hp loco for freight traffic, called the 'WAG-7'. This loco is already under manufacture at CLW, and can operate at speeds upto 100km/h.

A Technological Challenge for theRailway Engineer

Since Mumbai Division is the only division on IR to have DC overhead supply, there is a need to change from DC to AC (or vice-versa) for trains going out of (or coming into) Mumbai. This changeover takes place at three locations. On the Central Railway route towards north and east, this change takes place at Igatpuri -- on the platform -- in the form of change of the locomotive. On the south-bound route, the changeover is to a diesel loco, at Pune station. But the most interesting is the changeover on the Western Railway route, towards Vadodara/Delhi. This change happens while the train is in full motion -- without any stopping or jerks whatsoever. To achieve this, the trains on Mumbai Central - Vadodara / Ahmadabad route are operated by 'dual-traction' locos of WCAM series. (BG, DC and AC traction, Mixed service). The changeover takes place just north of Virar, over a neutral section, while the passengers inside the train normally remain oblivious of such a major (technical) happening!

The Numerals

After having discussed and understood the alphabetic nomenclature prevalent in naming the locos operating on IR, let us take a brief look at the numerals too. Today, most locos have a 5-digit number after the type-code. The first two digits (from left) also signify the type of the loco, and the remaining three digits denote the serial number in that category. Thus WAP-4 class locos always have numbers beginning 22, while WCG class locos start with 20. The new generation WAP-5 and WAG-9 locos have numbers in the 30 and 31 series.

Who makes these locomotives?

While most of the electric locos today are manufactured at CLW, some, for instance, WCAM-2, WCAM-3 and WAG-5-HB, are made by BHEL. Similarly, while CLW made most of the BG steam locos of the bygone era, many 'YP' class MG steam locos were made by Tata Engineering and Locomotive Company. Though TELCO no longer produces locomotives, the word 'locomotive' has remained etched in the name of the company. Similarly, while DLW has contributed to almost all diesel locos, some shunting locos were made at CLW.

With this basic understanding of the loco numbering system adopted on the Indian Railways, the readers will now be able to distinguish and recognize each type of loco separately, and perhaps, make their friends and relatives too more aware of the interesting intricacies of the Indian Railways, while continuing to enjoy their rail travel.