Trystan Casey
The third rail is the part of the subway track that is electric. It is located close to the ground and provides 600 volts of electricity to power subway cars and their ancillaries. The third rail is a safety hazard and can be deadly to anyone on the tracks. The risk can be mitigated through the use of platform screen doors, placing the conductor rail away from the platform, or covering the conductor rail. The third rail was first used in 1906 by Lionel electric trains, and is still used in many new systems, including the Copenhagen Metro, Taipei Metro, and Wuhan Metro.
| Characteristics | Values |
|---|---|
| Purpose | To provide electrical power to the power-train and ancillaries of the subway cars |
| Voltage | 600 volts DC |
| Risk | High risk of electric shock |
| Mitigation | Platform screen doors, placing the conductor rail away from the platform, covering the conductor rail |
| Conductor rail material | Special soft steel |
| Conductor rail length | 33 feet |
| Conductor rail weight | 100 pounds per yard |
| Return current | Usually flows through one or both running rails |
| Design | Third rail (current feed) and fourth rail (current return) |
| Contact shoe position | Below, above, or beside the third rail |
| Contact shoe type | Horizontal |
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What You'll Learn
Third rail systems are a hazard to anyone on the tracks
Third rail systems are a means of providing electric traction power to trains. They use an additional rail, known as a "conductor rail", which is placed alongside or between the rails of a railway track. This rail is electrified and therefore poses a hazard to anyone on the tracks.
The dangers of third rail systems have been recognised for some time, with early attempts to mitigate the risk including the use of bottom or side contact rails, which allowed the conductor rail to be covered, protecting track workers from accidental contact. Despite these measures, third rail systems remain a hazard to anyone on the tracks, including both workers and passengers.
The electrified rail presents a risk of electric shock, and high voltages above 1500 V are not considered safe. As a result, very high currents are required to transfer adequate power to the train, leading to high resistive losses and the need for closely spaced feed points. This creates a dangerous environment for anyone in close proximity to the tracks, as accidental contact with the electrified rail can result in serious injury or death.
The risk of electric shock can be mitigated through the use of platform screen doors or by placing the conductor rail on the side of the track away from the platform. Additionally, the conductor rail can be covered with a coverboard, a plank supported by brackets, to prevent accidental contact. However, coverboards are not always feasible due to their impact on the structure and loading gauge.
The hazards of third rail systems have been highlighted in several incidents, including a 1992 case in Chicago where a person walked onto the tracks at a level crossing and suffered electric shock, resulting in a significant financial verdict against the transit authority. In another incident, the Valhalla train crash of 2015, it is believed that the third rail penetrated the interior of a passenger car, contributing to the deaths of five passengers. These incidents underscore the critical importance of effectively managing the risks associated with third rail systems to ensure the safety of individuals on or around railway tracks.
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The third rail carries 660 volts of electricity
The third rail is also known as the contact rail, and it is made of special soft steel to secure high conductivity. The running rails are electrically connected to minimize resistance in the electric circuit. Contact shoes can be positioned below, above, or beside the third rail, resulting in bottom-contact, top-contact, or side-contact variations. The position of contact between the train and the rail has evolved over time, with early systems using top contact, and later developments adopting side or bottom contact to protect track workers and the conductor rail from the elements.
The third rail is an essential component of subway electrification, and its design has been refined over the years to enhance safety and efficiency. The voltage supplied to the third rail must be carefully considered to balance power transfer and safety concerns. While third-rail systems have been widely adopted, some countries prefer overhead wiring for their urban railways.
The third rail is a critical but hazardous component of subway systems. Its high voltage presents a risk to anyone on the tracks, and precautions must be taken to mitigate this danger. The risk can be reduced through the use of platform screen doors, strategic placement of the conductor rail, or covering the rail with a coverboard.
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$798.98
The third rail is located close to the ground
The third rail is a crucial component of subway systems, providing electrical power to the trains and their ancillaries. Its location close to the ground poses unique challenges and safety considerations.
The third rail is typically located near the ground, and its proximity to the ground is an important factor in its design and operation. This placement is intentional and serves a specific purpose. The third rail needs to be close to the ground to facilitate the transfer of electrical power to the train. The electricity flows from the third rail to the train through a horizontal contact shoe, which is positioned between the rubber wheels of the train. This arrangement ensures a consistent and reliable transfer of electricity to power the train's systems.
The close proximity of the third rail to the ground introduces safety hazards, as it carries a high voltage of 600 to 1200 volts DC. This voltage is more than enough to be lethal to individuals who come into contact with it. To mitigate the risks associated with the electrified rail, several safety measures are employed. These include the use of platform screen doors, strategically placing the conductor rail away from the platform, and covering the conductor rail with a protective coverboard.
The third rail's location near the ground also presents challenges in terms of maintenance and operations. For example, rainwater can disrupt signals and require the temporary shutdown of the electrified third rail until the issue is resolved. Additionally, the third rail's proximity to the ground can make it more susceptible to debris, such as leaves, snow, or ice, which may accumulate and impact the smooth flow of electricity. Regular maintenance and cleaning are necessary to ensure the safe and efficient operation of the third rail.
The design and placement of the third rail have evolved over time to enhance safety and functionality. For instance, the New York Central Railroad, the Philadelphia Market-Frankford Line, and the Hamburg Hochbahn pioneered the use of bottom contact rails, also known as the Wilgus-Sprague system, in the early 20th century. This design helped protect track workers from accidental contact with the electrified rail. Subsequently, the Manchester-Bury Line introduced side contact rails, providing additional safety measures. These advancements demonstrate the ongoing efforts to improve the safety and reliability of subway systems, specifically concerning the electrified third rail.
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The third rail is interrupted at level crossings
A third rail, also known as a live rail, electric rail or conductor rail, is a method of providing electric power to a railway locomotive or train. It is typically used in mass transit or rapid transit systems, which are fully or almost fully segregated from the outside environment. The third rail can be located alongside or between the rails of a railway track.
To ensure the train still has power at all times, there is usually a pickup on each carriage, and trains using the third rail often have several power-pickups along their length. In the event that the train loses power, it will coast through the powerless section. The third rail ends shortly before the level crossing and starts again after the crossing.
To maintain a continuous power supply, cables connect each side of the gap in the rail. These gaps are necessary to ensure the safety of pedestrians and to prevent electric shocks, particularly in locations where individuals may have easy access to the tracks.
In some cases, level crossings are avoided entirely with third-rail systems, and alternative power sources such as overhead wires are used. For example, the Rotterdam Metro has outlying branches with numerous level crossings that utilize overhead wires for power transmission.
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The third rail is made of special soft steel
The third rail is an essential component of subway systems, providing electrical power to the trains and their ancillaries. However, it also poses a significant safety hazard, carrying enough electricity to be fatal. To mitigate this risk, various measures are employed, such as platform screen doors and coverboards.
The use of soft steel in the third rail also provides benefits beyond electrical conductivity. Soft steel is known for its malleability and ductility, making it easier to work with during the manufacturing and installation process. It can be shaped and formed without cracking or breaking, which is essential for creating the long, continuous rails required for subway systems. Additionally, soft steel's ductility allows it to withstand stress and strain without permanent deformation, ensuring the structural integrity of the third rail over time.
Furthermore, soft steel's lower carbon content contributes to its corrosion resistance. In the corrosive environment of subway tunnels, soft steel's resistance to rust and oxidation helps maintain the integrity of the third rail and minimizes the need for frequent maintenance and repairs. This corrosion resistance is especially important given the presence of moisture and rainwater, which can sometimes infiltrate the subway system and affect the electrical components.
The choice of soft steel for the third rail is a testament to the engineering considerations that go into designing a safe and efficient subway system. By prioritizing conductivity, workability, and corrosion resistance, the use of soft steel helps ensure the reliable operation of subway trains while also mitigating potential electrical hazards. This balance of properties makes soft steel a crucial material in the functioning of modern subway infrastructure.
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Frequently asked questions
The third rail is the part of the subway track that provides electrical power to the subway cars.
The third rail provides electrical power to the subway cars, including the power-train and ancillaries.
The third rail is energized at 600 volts DC, providing power to the subway cars. The running rails are electrically connected using wire bonds or other devices to minimize resistance in the electric circuit.
The third rail is located close to the ground, typically at the side of the track or in the center of the track.
Yes, the third rail is hazardous and can deliver an electric shock. It carries enough electricity to kill a person.
