Classification of Locomotives (WDM 3A, WAP 7, WAG 9)

• In India, there are different ways of classifying the locomotives. Based on various factors locomotives are classified.
• Locomotives are classified according to their track gauge, motive power, the work they are suited for and their power of model number.
• This is indicated by the class name which provides the information about the locomotive. It comprises of 4 – 5 letters.
• The first letter indicates the track gauge . The second letter indicates their motive power (Diesel or Electric). The third letter indicates the kind of traffic for which they are suited for example goods, passengers, mixed or shunting. The fourth letter indicates locomotives chronological model number or nowadays the fourth letter indicates the horse power of the locomotive.

• In Extreme case the locomotive have the fifth letter which indicates the technical variant or subclass or subtype. Some of the indication of fifth letter is like ‘A’ for 100 hp, ‘B’ for 200 hp, ‘C’ for 300 hp, etc. So in this scheme, a WDP-3A refers to a 3100 hp loco, while a WDM-3F would be a 3600 hp locomotive.

These letters are further classified in detail. They are as follows:
1. The first Letter (Gauge)

• W – Indian Broad Gauge (W – wide gauge of having width of 5ft 6in). 
• Y – Meter Gauge ( Y – Yard Gauge of having width of 3ft or 1000 mm ).
• Z – Narrow Gauge ( Having width of 2ft 6in ).
• N – Narrow Gauge ( Having width of 2ft also called as ‘Toy gauge’)

2. The Second Letter (Motive Power)

• D – It stands for ‘Diesel’
• C – It stands for ‘DC Electric’. It can run under DC overhead line only.
• A – It stands for ‘AC Electric’. It can run under AC overhead line only.
• CA – It indicates both ‘AC and DC’. It can run under both AC and DC overhead line. It is consider as a single letter.
• B – It indicates ‘Battery Electric Locomotive’.

3. The Third Letter (Job Type).

• G – It indicates ‘Goods’.
• P – It indicates ‘Passengers’.
• M – It indicates ‘Mixed’ i.e. both goods and passengers 
• S – It indicates ‘Shunting’. It also known as switching engines.
• U – It indicates ‘Electric Multiple Unit’. It is use to carry the commuters in the city suburbs.

Followings are some of the examples :
(i). The locomotive with “WDM 3A” name, which means

• W – Broad Gauge.
• D – Diesel Motive Power.
• M – Suitable for both Goods as well as for Passengers.
• 3A – the Locomotive’s Power is 3100HP.

(ii). The locomotive with “WAP 5” name, which means

• W – Broad Gauge.
• A – AC Electric Traction Motive Power
• P – Suitable for Passenger Service.
• 5 – Locomotive is chronologically the fifth electric locomotive model used by the railways for passenger service.