Catenary and overhead line equipment
The overhead contact system (OCS) — also called overhead line equipment (OLE) or overhead contact line (OCL) — supplies electrical power to trains through continuous contact between wire and pantograph.
The OCS is not structurally part of the track superstructure, but it is tied to the permanent way throughout: mast spacing and foundation design follow track geometry, and wire height is measured relative to the rail running surface.
Two wires
The contact wire runs at a nominally constant height above the rail — 5,000–5,500 mm depending on the network standard — and is the surface against which the pantograph slides. It is made of hard-drawn copper or copper alloy, with a cross-section of 100–150 mm².
At the speeds and current densities involved, contact wire wear is the principal life-limiting factor. Wire is replaced on a planned cycle based on measured wear rate rather than fixed time intervals.
The catenary (messenger) wire hangs between mast supports in its natural parabolic curve and carries the contact wire below it via droppers of varying length. The droppers are longer at mid-span, where the sag is greatest, and shorter near the masts — holding the contact wire horizontal throughout.
Stagger
The contact wire is deliberately zigzagged laterally by ±200–300 mm rather than running directly above the track centreline. The stagger distributes pantograph wear evenly across the carbon strip width.
Without it, wear would concentrate at a single point on both the contact wire and the pantograph strip.
High-speed design
Above 250 km/h, catenary design becomes a wave propagation problem. Pantograph passage creates a mechanical wave in the contact wire that must travel faster than the train to prevent resonance and wire uplift.
Contact wire tension of 27–31 kN and precisely controlled dropper spacing are required to achieve adequate wave speed.
Contact wire uplift must remain within limits to maintain continuous electrical contact; loss of contact at high speed generates arcing that erodes both the contact wire and the pantograph strip. EN 50119:2020 governs OCS design, test methods and acceptance criteria.
Four voltages
Four traction supply voltages are in service on the European network: 750 V DC and 1,500 V DC on urban and some regional lines; 3 kV DC on parts of Italy, Spain and central Europe; 15 kV AC at 16.7 Hz in Germany, Austria, Switzerland and Scandinavia; and 25 kV AC at 50 Hz on most high-speed lines and across much of central and eastern Europe.
OCS design differs significantly between these systems in conductor cross-section, insulation clearances and tension levels. Multi-system locomotives and electric multiple units (EMUs) carry transformers and converters capable of operating under two or more supply voltages, but the OCS itself is system-specific.
Cost and deployment
As of 2024, 57.6% of the EU rail network is electrified (Eurostat).
OLE installation costs on existing routes range from EUR 500,000 to EUR 2 million per track-kilometre. The variation is driven primarily by civil clearance works — raising bridge soffits and tunnel portals to accommodate the contact wire height requirement.