The OHE Inspection Car carries out a distinct, annual round of highly specific geometric checks at locations that carry disproportionate risk if maladjusted — turnouts/crossovers, section insulator assemblies, overlaps, overline structures, and splices. Points and crossings in particular receive special attention because mal-adjustment of OHE at these locations can lead directly to pantograph entanglement.
7.1 Maintenance of Turnout / Crossover
| Parameter | Standard Value |
|---|---|
| Height of contact wire towards turnout, at/near obligatory structure | Turnout contact wire = Main line height (H) + 50mm |
| Turnout span (max) | 54 m |
| Pantograph clearance from turnout/crossover wire while on main line | H + 50mm |
| Stagger of contact wire at obligatory structure — main line | 200mm max |
| Stagger of contact wire at obligatory structure — turnout | 300mm max |
| Movement of tower wagon from main line to turnout / turnout to main line (take-off/take-on) | 650mm to 720mm from centre line of pantograph |
| Vertical distance, register-arm axis to contact plane — with drop bracket | 300mm |
| Vertical distance, register-arm axis to contact plane — with steady arm clamp | 250mm |
| Stagger of section insulator of turnout/crossover | ±100mm |
| Track separation at section insulator — runners towards centre of turnout | 1.65 m min |
| Track separation at section insulator — runners away from centre of turnout | 1.45 m min |
| Setting distance (implantation) of obligatory structure | 3.0 m min |
| Distance of 'G' jumper from obligatory structure | 5.6 m |
| Length of 'G' jumper | 4.0 m |
| Track separation at obligatory structure | 150 to 700 mm |
- The pantograph must NOT touch the turnout/crossover contact wire while the train passes on the main line — this is the entire safety rationale behind the H+50mm turnout height rule.
- Sag of the section insulator at turnout/crossover: height should be the same as at support — i.e. zero additional sag.
- Sag of contact wire follows RDSO's standard dropper schedule.
- Observation at the obligatory location: register-arm tube should be horizontal, bracket plumbed to a depth of 25-30mm.
- Length of pipe provided in the hex tie rod of the limiting device (to bridge redundant length) follows SMI No. TI/MI/0035 Rev.1.
- Condition of ATD of the turnout/mainline OHE: must be free to move.
7.2 Maintenance of Section Insulator Assemblies
- Clean insulators and replace badly chipped or even slightly chipped insulators; check runners for flash marks; observe for hit marks on runners.
- Check for excessive contact wire wear near anchor loops — find the reason and attend it.
- Check level of the section insulator cross-beam assembly with a spirit level and adjust if necessary.
- Tighten PG clamps of droppers and stiffeners.
| Parameter | Standard Value |
|---|---|
| Clearance, runner to runner | 460 mm max |
| Clearance, contact wire to runner | 230 mm |
| Encumbrance at section insulator | Not less than 450 mm |
| Stagger of section insulator | Zero |
- Check the pantograph passes smoothly under the section insulator; adjust runners for level and smooth passage if not.
- Measure and record IR values of the section insulator and 9-ton insulator — should be more than the permissible limit.
- Record height of the section insulator from rail level; note the core insulator and cut-in-insulator make.
7.3 Maintenance of Overlap OHE and RRA Clamp
| Parameter | Standard Value |
|---|---|
| Distance between parallel contact wires — Un-Insulated Overlap (UIOL) | 200 mm |
| Distance between parallel contact wires — Insulated Overlap (IOL) | 500 mm |
| Stagger of in-running contact wire — tangent track | ±200 mm |
| Stagger of in-running contact wire — curved track | ±300 mm |
| Overlapping of contact wire | 2 to 9 m |
| Number of PG clamps required in 'G' jumper | 8 (minimum) |
- The cut-in-insulator of catenary and contact wire must NOT have longitudinal shift (eccentricity) — it should be zero.
- Check proper seating and tightness of connections at PG clamps of 'G' and 'F' jumpers — tighten if loose/seating issue.
- Ensure adequate looping in the jumper with 8 nos. of PG clamp in the 'G' jumper — if length is short, replace it; if PG clamp count is less than 8, add more. Ensure a proper shape of the jumper.
- Check the contact wire in the RRA clamp for hair-cracks using a magnifying glass; check for cracks/damage/sharp edges/defects in clamp fitting with the same tool.
- Check for deformation of the RRA clamp — replace if defective. Check for crack/damage to contact wire near the RRA clamp — change the contact wire, provide a splice, or a contact wire ending clamp.
Exam Focus — The Memorable Mnemonic Line
A Hindi field mnemonic is worth remembering as a quick recall trigger for this exact rule: 'JAHAN MILE DO TENSION LENGTH, WAHAN HO G JUMPER WITH DOUBLE (PG CLAMP) STRENGTH' — wherever two tension lengths meet (i.e. an overlap), the G jumper needs double PG-clamp strength. This anchors the '8 PG clamps minimum in the G jumper' rule.
7.4 Annual Maintenance of Overline Structure/Tunnels and Clearances Under Overline Structure
- Check horizontal and vertical clearances — adjust if required. Check for flash marks on the underside of the bridge structure.
- Check the gradient of contact wire on either side — should NOT exceed 3mm/m. Check clearance of catenary/contact wire (whichever is nearest to structure) at both ends.
- Check that false catenary (contact wire) is provided; check that an insulated sleeve is provided.
- Check smoke screens are properly secured with adequate clearance (attended by the Engineering Department if not); check condition/availability of the 25000V danger board on the screen.
- Check the underside of the bridge for any foreign material hanging; check the side gap on FOB/ROB for water or foreign material.
- Minimum FOB/ROB headroom from rail level is maintained as per SOD (Schedule of Dimensions).
7.5 Splices
- Check for cracks, other casting defects, and abnormalities — replace if found.
- Check tightness of the stainless-steel stud.
- Check that no slipping of the two contact-wire ends has occurred, viewed through the top window — there should be NO GAP between the two contact wire ends.
- Contact wire splices should NORMALLY NOT be re-used.
- For catenary splices, check tightness of the right-hand and left-hand joint sockets.
7.6 General Annual Maintenance of OHE by Inspection Car
- Check stagger of contact wire and catenary wire — as per SED; check contact wire height by height gauge — as per SED.
- Check all nuts, bolts, 'U' pins, split pins — tighten if loose, provide missing items. Check for kinks in the contact wire — remove with a kink remover if observed.
- Check the 'G', 'C', 'F' jumpers for deformation, strand breakage, shaping, PG clamp tightness, and rusting of nuts/bolts/washers.
- Measure contact wire diameter vertically by micrometer; check hogging of contact wire and adjust by one-end dropper; check height of contact wire in mid-span (calculate pre-sag).
- Check gradient of the contact wire profile — should be 3mm/m; check twist of contact wire — remove with a twister.
Exam Focus — UIOL vs IOL, and the Overlap Range
A frequently-confused pair: Un-Insulated Overlap (UIOL) parallel wire spacing = 200mm, Insulated Overlap (IOL) = 500mm — insulated needs more than double the spacing, since it must maintain electrical clearance between the two separately-fed sections, not just mechanical clearance. The overlap length itself (2 to 9m) is a range, not a fixed figure — don't confuse it with the parallel-wire spacing numbers above.