Most OHE items are attended to during annual maintenance and periodical overhaul. Some items, however, require more frequent attention — this chapter covers those special, higher-frequency checks, plus the two dedicated seasonal (pre-summer, pre-monsoon) checklists.
5.1 Insulators — Cleaning Frequency by Pollution Level
- Normally, insulators need cleaning once a year along with the annual maintenance schedule, where there is NO pollution.
- Where pollution is NOT high, the interval may be three months or longer, depending on the degree of pollution in the area.
- Where pollution is HEAVY, more frequent cleaning is required.
- The affected section should be divided into various zones based on the degree and nature of pollution, and the periodicity of insulator cleaning fixed suitably per zone.
5.2 Section Insulator — Quarterly
Section insulators on main lines, neutral sections, passenger yards, and sidings should be attended to ONCE IN THREE MONTHS as follows:
- Clean insulators and replace badly chipped or even slightly cracked insulators.
- Check runners for flash marks.
- Check level of the assembly and adjust as required.
- Check for excessive contact wire wear near the anchor clamp.
- Tighten the PG clamps of droppers and stiffener properly.
- Check that the pantograph passes underneath the section insulator smoothly.
5.3-5.7 Other Special Checks
- 5.3 Isolating Switches at Yards/Loading Siding: continuity and soundness of earth connections should be checked ONCE A MONTH.
- 5.4 Bi-Metallic Clamps: checked for tightness and signs of overheating ONCE IN THREE MONTHS.
- 5.5 Earth Connections: apart from general inspection during foot patrolling, all bond and earthing connections should be specially checked for continuity and soundness ONCE IN SIX MONTHS.
- 5.6 OHE Support on Steel Girders: examined as often as possible depending on traffic movement.
- 5.7 Bird Nests: precaution should be taken during the nesting season, and nests removed as soon as possible.
5.8 Pre-Summer Checks
| Item | Check |
|---|---|
| Overhead crossing | Check all power line crossings for broken and loose guard wire |
| Bird nest / kite threads | Remove all kite threads and polythene from OHE, transmission line, and nearby structures (FOB/ROB/platform sheds etc.) |
| ATDs | Ensure free movement of ATDs; replace jammed/over-riding ATDs. Proper Z & Y adjustment should be done |
| Jumper | Excessive loose jumpers should be attended |
| Anti-creep | Anti-creep having excess sag should be re-tensioned |
| Turnout/Crossover | All turnouts and crossovers should be checked |
| FOB/ROB | Clearance of the OHE under FOB/ROB should be checked; protective screen, cable/wires should be properly secured |
5.9 Pre-Monsoon Checks
- Check the condition of insulators, especially section insulators at major yards having mixed type of traction.
- Check the overline structure for any water leakage onto the OHE.
- Trim tree branches near the OHE.
- Check the condition of embankments with respect to stability of the mast.
- Ensure proper drainage of rainwater surrounding the OHE foundation/mast.
Exam Focus — The Frequency Ladder for Section 5
A clean frequency ladder across Section 5's special checks: isolating switch earth continuity = MONTHLY (most frequent) → section insulator, bi-metallic clamps = QUARTERLY (3-monthly) → earth connections (bond/earthing soundness specifically) = HALF-YEARLY (6-monthly) → insulator cleaning = YEARLY in unpolluted areas (with quarterly-or-more in heavy pollution zones, since pollution overrides the default). Pre-summer and pre-monsoon checks are seasonal (twice-yearly, timed to the season) rather than fixed-interval — a distinct category from the calendar-based frequencies above.