dead section

A dead section is a short, unpowered length of track installed within a neutral section of an electrified railway line. It exists to break electrical continuity and prevent short circuits or arcing when pantograph equipment transitions between sections powered by different phases or voltages. The dead section itself carries no current and is typically 1 to 2 metres long, though exact length varies by rail authority and voltage class.

On AC systems running at 25 kV or 15 kV, dead sections separate sections that are fed from different transformer substations or phase groups. As a train's pantograph moves from one powered section into a dead section, power to the train is momentarily lost, then restores as the pantograph enters the next powered section. On DC systems, dead sections mark transitions between positive and negative return rails or between sections of opposite polarity. The train's onboard equipment must tolerate these brief power interruptions without stalling or losing traction.

The primary risk in a dead section is arcing and electrical flash if the pantograph makes contact while straddling two different potentials. For this reason, dead sections are kept as short as practicable, and many modern trains have on-board energy storage, such as supercapacitors or small batteries, to maintain traction through the dead zone without interruption to the driver or passengers. Older rolling stock simply coasts through, relying on its momentum and the speed restriction enforced at that location.

Dead sections are marked on trackside signage and on the lineside with distinctive insulators and warning boards. Maintenance is critical: loose bolts, corrosion, or poor bonding in a dead section can cause unexpected power loss or dangerous voltage spikes. The term dead section is used almost exclusively in European railway practice; North American transit systems more often use the term neutral section to describe the whole transition zone, with less precise subdivision.