This chapter covers two things: the periodic inspection/maintenance schedule structure used on EMU/MEMU traction equipment, and the two families of electrical contactors (electro-magnetic and electro-pneumatic) that make and break circuits throughout the rake.
Maintenance Schedule Structure
Traction motor maintenance (and, by the same pattern, much of the rest of the electrical equipment) on AC EMU/MEMU follows a fixed cycle of progressively deeper inspections, each named for how far apart they occur:
- Trip Inspection — every 10 days: the most frequent, lightest check.
- IA Schedule — every 45 days.
- IB Schedule — every 90 days.
- IC Schedule — every 180 days: the deepest of the four periodic schedules, before full overhaul.
Do's and Don'ts — Traction Motor Maintenance
- Always use a torque wrench for tightening nuts & bolts to the recommended value — not judgement by feel.
- Ensure replacement carbon brushes are the same grade as the ones being replaced.
- Use a shock pulse meter (SPM) to monitor bearing condition, and keep a record of readings over time.
- Remove carbon brushes before applying any solvent for cleaning the motor.
- Never mix carbon brushes of different grades on the same traction motor.
- Never reuse used grease or lubricant oil.
- Never carry out commutator resurfacing/turning unless grooves, stepped wear, or ovality are actually found — don't resurface as routine.
- Never run the motor at high speed under no-load for long periods — risk of roller skid, scuffing, and premature bearing failure.
- Never use a higher-voltage meggar than specified for insulation testing.
Electrical Contactors — Two Families
Two distinct contactor families make and break circuits throughout an AC EMU/MEMU rake, and exam questions often hinge on telling them apart correctly.
- Electro-magnetic (EM) contactors — operate purely on energisation of an operating coil; arc quenching is done via a blow-out coil working together with an arc box. Used for the main compressor circuit (CC1), auxiliary compressor circuit (CC2), lights, and fans.
- Electro-pneumatic (EP) contactors — use compressed air (pneumatic) actuation, controlled electrically, rather than a purely magnetic operating coil. Used in the main traction power circuit, where higher currents demand a more robust actuation mechanism.
Energy Conservation in EMU/MEMU
- Adhere strictly to the coasting and powering boards provided for EMU/MEMU sections.
- Switch OFF power whenever the rake is stabled or line clear is delayed more than 30 minutes.
- Switch OFF the rear Motor Coach while hauling empty stock to shed movement.
- Run at maximum permissible speed and coast wherever possible; approach the foot of a gradient at max permissible speed to reduce traction motor current while climbing.
The guard/maintenance staff also play a role — switching off fans and lights as service completes, and avoiding brake binding in the formation. Broader measures include energy-conservation awareness posters for commuters, fluorescent lighting in place of incandescent lamps, rail-flange lubrication to reduce frictional losses, and energy meters to monitor specific consumption.