This chapter covers two practical, frequently-tested areas: the real maintenance checklist followed for AC coaches at primary/secondary depots, and the causes and prevention of electrical fires in coach wiring.
AC Coach Maintenance Checklist
Real Depot-Level Requirements
- AC coaches must leave the Primary Depot with BOTH alternators working. If one can't be repaired at a secondary depot, sending the coach with just one working alternator requires officer-level approval, and that alternator must be fully functional with the coach properly pre-cooled first.
- Belt count requirement: 6+6 belts on alternators from Primary Depot, minimum 5+5 from Secondary Depot — with facilities to change belts on the rake itself.
- SMF (VRLA) battery cells: full-load and no-load voltage of each cell recorded monthly for 3 months; if no abnormal variation, recording frequency drops to once every 3 months.
- ACCI/ACCA staff (AC Coach attendants/technicians) must maintain a log book recording all unusual occurrences, and undergo a standardised one-week training on equipment operation and failure handling.
- WRA (Water Retention/Roof-mounted assembly) working must be checked on arrival at primary/secondary depot, confirmed before the rake is placed at the platform.
- Unit Exchange Spares (UES) must be available and registered at every depot, and failure analysis of major equipment must be reported to RDSO periodically.
Fire Causes & Prevention
Excessive current in coach cables is the only real cause of electrical fires — either from undersized cables (eliminated by design/spec compliance to EL/TL/48) or a short circuit. Since cable sizing is standardised, short circuits are the main practical concern, and the response has three layers: prevent the short in the first place, ensure protective devices isolate any fault instantly, and use fire-retardant materials so that if a fire does start, it doesn't spread.
- Earth checking: the train lighting system is a two-wire unearthed system, so genuinely causing a short circuit requires TWO earths — one on positive polarity, one on negative — checked separately.
- Light points, fan points, and switches are especially prone to earthing in metal-bodied coaches — proper fitment attention at the lamp holder, fan brush holder, and toggle switches minimizes this.
- Air clearances: minimum 10mm between any live part and the coach body, 4mm between parts of opposite polarity (EL/TL/48 clause 3.9.4) — inadequate clearance risks a tool-induced short during routine maintenance.
- Coach insulation test: insulation resistance measured with a 500V megger, following a defined test procedure — a genuinely testable procedural fact.
Important Caution — Never Chip Cable Insulation
A dangerous maintenance-staff habit is explicitly flagged: chipping cable insulation mid-length to test for a live feed. This leaves a permanent scar that re-taping won't properly fix. Correct practice is to test feeds only at terminals, never by damaging the insulation midway along the cable.
Exam Focus — Detecting a Bad Crimped Joint
A poor crimped joint causes heating that damages cable insulation over time. The practical detection method: feel the temperature of the socket while full load current is passing through it — a hot terminal indicates either an improper connection or a bad crimped joint.