The electrified rail threatens electrocution of anyone wandering or falling onto the tracks. A very high current must therefore be used to transfer adequate power, resulting in high resistive losses, and requiring relatively closely spaced feed points ( electrical substations).

īottom contact third rail in the sheath insulator The contact shoe enters from the leftīecause third rail systems present electric shock hazards close to the ground, high voltages (above 1500 V) are not considered safe. The position of contact between the train and the rail varies: some of the earliest systems used top contact, but later developments use side or bottom contact, which enabled the conductor rail to be covered, protecting track workers from accidental contact and protecting the conductor rail from frost, ice, snow and leaf-fall. Tapered rails are provided at the ends of each section, to allow a smooth engagement of the train's contact shoes. The conductor rails have to be interrupted at level crossings, crossovers, and substation gaps. Contact shoes can be positioned below, above, or beside the third rail, depending on the type of third rail used: these third rails are referred to as bottom-contact, top-contact, or side-contact, respectively. The running rails are electrically connected using wire bonds or other devices, to minimise resistance in the electric circuit. Elsewhere in the world, extruded aluminium conductors with stainless steel contact surface or cap, is the preferred technology due to its lower electrical resistance, longer life, and lighter weight. In North America, the conductor rail is usually made of high conductivity steel or steel bolted to aluminium to increase the conductivity. The traction current is returned to the generating station through the running rails. The trains have metal contact blocks called collector shoes (also known as contact shoes or pickup shoes) which make contact with the conductor rail. The conductor rail is supported on ceramic insulators (known as 'pots'), at top contact or insulated brackets, at bottom contact, typically at intervals of around 10 feet (3.0 m). On most systems, the conductor rail is placed on the sleeper ends outside the running rails, but in some systems a central conductor rail is used. Third-rail systems are a means of providing electric traction power to trains using an additional rail (called a 'conductor rail') for the purpose. 3.6 Russian Federation and former Soviet Union.2.6 Electrical considerations and alternative technologies.

Step rails