Electrical System of Coaches:
What are the main components of Lead Acid Cell?

Ans. Main Components of Lead Acid Cells are:

  • Positive Plates which are tubular in shape made of PBO2
  • Negative Plates usually consists of a lead grid into which active material of Sponge lead is pressed.
  • Separators which are made by Synthetic used between positive and negative plates.
  • The container is made of hard rubber or PPCP with the high insulating strength to resist acids which are used as Electrolyte.
  • Cells cover which covers container having vent plugs and level indicator.
What type of batteries are used in TL coaches? Explain briefly about each one of them?
  1. Ans.
    In TL coaches two type of batteries are used. They are VRLA & SMF batteries. VRLA batteries
    These are the Valve Regulated Cells which works on Oxygen Recombination Principle.
SMF batteries:
  • To overcome problems of frequent topping up and leakage of electrolyte sealed
    maintenance free batteries are developed.
  • The electrolyte in SMF batteries is in immobilized form and these can be used in any position.
What do you mean by PELE box and when it is utilized?

Ans. The equipment available in PELE box are:


These equipment are used in emergency conditions of train service. This box is kept in the Guard Compartment.

What are the Safety Checks in under gear and batteries?

Ans: Alternator

  • Alternator safety chains
  • Suspension pin with anti-rotation plate and cotter pin
  • Suspension pin with nylon bushes
    Alternator pulleys
  • Axle pulley :
  • Axle pulley with bolts and split pins.
  • Battery box:
  • Condition of battery box channels
  • Check nuts with split pins.
  • Availability of nuts & bolts with split pins
  • Availability of nuts & bolts with split pins of other under gear electrical suspension equipment.
How to check Earth fault with Double Test Lamp?

Ans: Double test lamp having three leads. Centre lead should be connected to earth, left side lead to be connected on the positive side (+ve), right side to be connected on the negative side (-ve) If both bulbs glow dimly it indicates no earth in the coach. If left side bulb glows brightly it indicates negative earth (-ve) in the coach. If right side bulb glows brightly it indicates positive earth (+ve) in the coach.

What are the safety items to be inspected on battery?

Ans: Safety items to be checked on battery are full complements of battery box fixing bolts and its tightness, observation of its bottom plate and side plates for damage, full tightness of cell packing, proper securement of anti-theft arrangement and battery box cover, full tightness of inter-cell connections with double fasteners, correct size of battery fuse, elimination of earth leakage and maintenance of correct polarity, Etc.

What are the safety items to be inspected on Rotary Junction Box?

Ans: Safety items to be checked on rotary junction box are the full tightness of all terminal connections, provision of the correct size of HRC fuses, maintaining the correct polarity of incoming and outgoing cables, avoiding earthing and shorting of cables.

Why earthing is necessary for any electrical equipments, domestic installation & service building etc? For TL coaches what is the minimum I.R. value required for new wiring?

Ans: To drain away any leakage of currents due to poor insulation and to save human life from dangerous shock and also to avoid burning of electrical equipment. The minimum IR value required for wiring is 2MΩ’s and minimum IR value required in service for giving coach fit for service is 1MΩ.

Practically demonstrate to use a Fire extinguisher?
  • P -Pull the pin at the top of the extinguisher.
  • A -Aim the nozzle towards the base of the fire.
  • S -Stand approximately 8 feet away from the fire and squeeze the handle to discharge the extinguisher.
  • S -Sweep the nozzle back and forth at the base of the fire.
What are the precautions to be taken before starting work on electrical installations?

Ans: Before starting any electrical works on installations disconnect the power supply to the Electrical equipment and discharge & connect earth. If any capacitors are connected, it has to be discharged properly. Test with meters for any availability of supply then start the work.

How do you conduct insulation resistance test on 100 VA inverter used for Laptop and mobile charging sockets used in RC SG coaches?

Ans: The insulation resistance of the inverter shall be measured with 500v megger as given below: a) Between input terminals shorted together and the housing with the output being kept in open circuit condition.
b) Between the output terminals shorted together and keeping the input terminals in open circuit. The insulation resistance values measured thus shall not be less than 10 Mega ohms in each test.

Write about the working principle of TL/AC alternator?

Ans. The core of the stator which is completely embraced by the field coils will retain a residual magnetism if excited by a battery once.

The flux produced by the filed coils find its path through the rotor. When the rotor has rotated the passage of rotor teeth and slots, alternatively, under the field, offers a varying reluctance path for the flux produced by the field coils.

The flux, which varies periodically, links with AC coils and induces an alternating voltage in AC coil. The frequency of the induced voltage depends on the speed of the rotor, whereas the magnitude depends on the speed of the rotor and the level of excitation.

The field is controlled by the regulator to attain desired output voltage by means of positive feedback again.

What are the precautions to be taken while loading and unloading of alternator?

While unloading and loading alternator, see that the terminal box and pulley should not be broken.The alternator to be loaded in a correct way that bushes to be provided in proper place.While loading and unloading proper precautions to be taken not to fall on ground otherwise
men/materials will be injured/damaged.See that the anti-rotating clamp provided on trolley coincides with alternator suspension pin.

Replace the worn out alternator and alternator suspension bracket bushes.See that the alternator should not have played with proper washers in improper place to align the axle pulley.Safety chains and cotter pins to be provided without fail.

Give important measures adopted by railways for prevention of fires in TL coaches?
  • Ans.
    Cable sizes have been standardized.
  • Provision of fuse on both positive and negative side in FDB
  • Use of self-extinguishing PVC cables.
  • Provision of rubber grommets at points where the cable enters through metal members in the coach.
  • Proper crimping at the cable terminals.
  • Air clearance of 10 mm between live part and earth and between parts of opposite polarity.
  • Replacing of cables with any joints, noticed during POH.
  • Re-wiring of the coach planned on the basis of cable life of 15 years.
  • Use of Flame retardant Insulation tape.
  • If I.R. value of wiring is less than 1M, rewiring should be taken up.
What are the major train lighting equipment available in Self Generating coaches?

Ans. The major train lighting equipment in coach are

  1. Alternator
  2. Rectifier cum Regulator Unit
  3. Battery
  4. Axle Pulley
  5. Rotary/ Roof Junction Box
  6. Underframe Junction Box
  7. Fans
  8. Lights
  9. EFT
  10. BCT
Explain the procedure for through feeding in TL coaches in case of an adjacent coach is dark/dim?

Ans: The detailed procedure of emergency feed extension is given as under

Action to be taken in healthy coach

The availability of power supply in the emergency feed terminal should be ensured.Only one dark coach should be extended feed supply from one healthy coach.Before connecting, the polarity of the health coach as well as dark coach shall be checked.

L-II circuit of the healthy coach shall be switched off before connecting supply to dark coachThe rotary switch of (socket paralleling main) SPM-I and II shall be kept in ON position.Action to be taken in defective coach and feed extension.L-II and fan circuit of the dark coach shall be switched off before connecting supply from the health coach.

The rotary switch of (socket paralleling main) SPM-I and II shall be kept in ON position.The L-I circuit is having essential/emergency lighting circuit. This includes all lavatory lights 50% of compartment lights, and night lights in all types of IInd class coaches.Remove (+ve) fuse from battery box and )-ve) the main fuse from the junction box to disconnect the power supply to/from the battery.

The earth fault shall be checked up with the help of a testing lamp. If earth fault is there then feed extension should not be done.The feeding shall be given to L-I circuit only of the dark coach from the health coach.The defective coach shall be attended and cable should be removed at the first available
opportunity by TL staff.

The size of the cables for the feed extension shall be of 16 sq.mm PVC Aluminum /2.5 sq.mm elastomeric /2.5 sq.mm e-beam copper cables.The length of the wire for feed extension shall be 2×1.5 meter (for both terminals). The length of the cable shall not be more than 1.5 meters.Both ends of the cable shall be provided with the suitable size of the lug.The cable shall be secured tightly by the screws or bolts, nuts, and plain washer. The proper tightness of the connections should be ensured.

Write about the LED-based Emergency Lights provided in TL & AC Coaches?

Ans: The general lighting inside the TL and AC coaches is provided by 110V DC supply with battery backup system. But during extreme emergencies like derailment and accidents etc. or regular supply system failure, causing total darkness inside the coach.

To facilitate the easy exit of passengers and their immediate rescue, during such situations an emergency light unit (E.L.U) system is developed to provide illumination which is located inside the coaches at the passage and on the doorways for use of movement of passengers.

Emergency light consists of LED-based lights working on 12V DC supply by the battery. The charging of the battery 12V, 12AH is done with 110V DC/ 12V DC, DC-DC converter. When the coaches equipment working satisfactorily the 12V battery will be charging with the help of coach supply. This unit will switch “ON” automatically on failure of the normal supply system.

What happens if electrical connection or electrical joint is loose?

Ans: due to a loose connection at joints resistance at that point will increase thereby the I2R losses are more and develops heat. The total wiring may burn.

What are the precautions to be taken while working in RE area?


No one shall attempt to work on any overhead line running alongside the electrified tracks without taking special precautions of earthing on both sides of the work.Minimum 2m electrical clearance from live OHE of the adjacent track or any other equipment nearby must be maintained.

During foggy/cloudy weather conditions, wear safety shoes, insulated rubber gloves, and tools with insulated handles should be used to protect from induction effect.Steel tape or metallic tape or tape with woven metal reinforcement should not be used.

Always carry the ladders/lengthy items in a horizontal position instead of vertical.
While attending to platform lights (in COP/OPEN area), the ladders shall be properly secured to avoid accidental fall in OHE.