Umair Gaines
In electrical engineering, a common rail is a shared path between different electrical routes in a circuit. In the context of railways, a common bond rail refers to the practice of electrically connecting rails to ensure proper signalling and power transmission. This is achieved through various methods, such as welding, bond wires, or specialised products like ERICO's CADWELD bonds, which offer superior protection against physical damage and electrical interference. These bonding techniques are crucial for the safe and efficient operation of electric trains, particularly in third-rail systems, where a semi-continuous rigid conductor provides power to the train through metal contact blocks called collector shoes.
Common Rail (Electricity) Characteristics and Values Table
| Characteristics | Values |
|---|---|
| Definition | A shared path between different electrical routes in an electrical circuit |
| Example | A device or circuit board might have a power rail or a ground rail, which components are attached to |
| Function | All the electrical charge flowing through different components is drawn from/collected into a single conductor line |
| ATX standard for PC power supplies | Defines a set of common rails as to ground the power, these rails are designated as COM and all have black wires |
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What You'll Learn
Third rail systems
A third rail system, also known as a live rail, electric rail, or conductor rail system, is a means of providing electric power to a train through a semi-continuous rigid conductor rail placed alongside or between the rails of a railway track. The third rail usually sits outside the two running rails, but in some systems, it is mounted between them. The electricity is transmitted to the train via a sliding shoe, which is held in contact with the rail.
The third rail system is commonly used in underground, metro, and urban transit systems, with shorter distances between stations. Over 30% of the UK rail network currently uses a third rail system, especially in dense urban areas. The system is generally associated with low voltage (rarely above 750 V) and is cheaper to install and maintain than overhead wire contact systems. The electricity is supplied with direct current (DC) electricity from lineside substations located between 1 and 6 miles apart, depending on the intensity of the train service.
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. The third rail may be identified by its different width, colour, or height compared to the two main rails, and it may have a protective cover, usually made of fibreglass, to prevent accidental contact.
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Electric Railway Improvement Company
The Electric Railway Improvement Company, also known as ERICO, was established in 1903 to supply power bonds, signal bonds, and related welding equipment to railroads, mining, and street railway industries. Over the next 112 years, the company expanded its capabilities and brands, promoting growth by venturing into new business areas.
ERICO's rail product line is the company's original business, and it has since developed a range of tools suitable for rail infrastructure applications. The company offers lightweight and easily transportable rail drilling machines in 2-stroke, 4-stroke petrol-powered, and 230V battery-powered electric variants. ERICO also provides a full range of rail profile templates, rapid clamping devices, and drills. Their portable rail grinders range from the SBG100 battery-powered grinder for light applications to the SBG150 2-stroke machine and the SBG200 4-stroke machine for heavier applications. The SBG200 is particularly well-suited for special track work, making it ideal for rail grinding and deburring operations.
ERICO's range of cable clips is designed for effective cable management within the track bed. They also offer rail bonds, including the CADWELD® exothermic welded rail bonds, which provide maximum protection against physical damage with superior shear strength, maximum corrosion resistance, and stable electrical resistance. The ERICONTACT® mechanical rail contact system is another one of their products, approved by several European rail systems.
Additionally, ERICO has developed lightning protection and grounding products applicable to rail signalling, telecommunications, and control applications. Their System 3000 Dynasphere is an advanced lightning protection system with proven performance in the field, including in the world's longest railway tunnel, the Gotthard Base Tunnel in Switzerland.
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CADWELD® bonds
In electrical engineering, a common rail (shortened to COM) is a shared path between different electrical routes in an electrical circuit. Electrical bonding is the practice of intentionally electrically connecting all exposed metal items not designed to carry electricity in a room or building. This is done to protect from electric shock and to minimize electrical arcing between metal surfaces with electrical potential differences.
ERICO's original business was supplying power bonds, signal bonds, and related welding equipment to railroads, mining, and street railway industries. ERICO's rail product line now supplies a range of railway infrastructure components to rail systems worldwide. This includes CADWELD® exothermic welded rail bonds, which provide an efficient field method for any electrical connection, from signal and power to grounding.
Rail joint bond kits provide all the items required to make a welded power bond connection to the head of the rail. These kits are essential for ensuring the safety and efficiency of the railway system by providing a reliable electrical connection.
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Track circuit connections
Track circuits are a crucial component of railway signalling systems, enabling the detection of the presence or absence of trains on a section of track. This information is essential for the signalling system to determine whether it is safe for another train to proceed. Each section of the railway forms part of an electrical circuit, with a voltage applied across the two rails. When a train enters the section, its wheels and axles create an electrical connection between the rails, causing the voltage to drop, which in turn turns off the electrical relay, indicating that the section is occupied.
Additionally, track circuit connections can be established using data pickup units (DPUs) in jointless track circuits. DPUs consist of tuned coils that detect the presence or absence of current in the adjacent rail, controlling the relay accordingly. This technology allows for more flexible placement of track circuits and avoids the need to change frequencies in a series of track circuits.
In some cases, track-circuit operating clips (TCOCs) are used as a simple safety measure. These clips are carried by heavy rail trains in Britain and consist of a length of wire connecting two metal spring clips that attach to the rails. During emergencies or obstructions, applying a TCOC to both rails indicates that the line is occupied, triggering the signalling system to respond accordingly.
The reliability of track circuit connections is crucial for railway safety and efficient train operations. Any failures or disruptions in these connections can lead to delays or, in the worst-case scenario, accidents. Regular maintenance and monitoring of track circuit connections are essential to ensure their proper functioning and to minimise the impact of potential failures.
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Electric shock hazards
In electrical engineering, a common rail (COM) is a shared path between different electrical routes in an electrical circuit.
The electrified third rail, located close to the ground, poses a substantial risk to anyone on the tracks. This hazard can be mitigated through various means, such as installing platform screen doors, strategically placing the conductor rail, or covering it with a coverboard. However, coverboards may not always be feasible due to structural constraints. Additionally, at level crossings, there is a risk of pedestrians accidentally coming into contact with the third rail.
To address these concerns, some rail systems have adopted overhead wires or lines instead of third rails. Examples of this can be seen in the southern region of British Rail, where freight yards utilized overhead wires to avoid the electrocution hazards associated with third rails. Similarly, certain electric trains in New York City switch from third-rail power to overhead lines outside of tunnels to mitigate health hazards from diesel locomotive exhaust.
However, it is important to note that even in the absence of a third rail, electric shock hazards can still exist. In certain cases, such as in Hillsboro, Oregon, issues with the rail system have resulted in electric shocks to seeing-eye dogs, indicating the potential for similar incidents involving humans.
To enhance safety, electrical bonding is employed in rail systems. Electrical bonding involves intentionally connecting exposed metal items to protect against electric shock. In the context of railways, bonding is achieved through various methods, including exothermic welded rail bonds, mechanical rail contact systems, and plug bonds for joint bonding. These bonding techniques help minimize the risk of electric shocks by ensuring that all metal objects are at the same potential, reducing the likelihood of dangerous voltage differences.
Furthermore, proper grounding is crucial in preventing electric shock hazards. Negative Rail Grounding Units (NRG units) are essential safety components that clamp fault voltages to the ground. Their absence in poorly designed rail systems can lead to lethal consequences, as voltage faults can make the entire rail system, including the cars, dangerous to touch.
In conclusion, electric shock hazards are a significant concern in rail systems, particularly those utilizing third rails. While mitigation strategies exist, such as platform screen doors and the use of overhead lines, the potential for electric shock remains. Proper electrical bonding, grounding, and the inclusion of NRG units are vital to enhancing safety and protecting individuals and infrastructure from the dangers of electric shock.
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Frequently asked questions
A common rail, shortened to COM, is a shared path between different electrical routes in an electrical circuit.
A device or circuit board might have a power rail or a ground rail, which components are attached to, so all the electrical charge flowing through different components is drawn from/collected into a single conductor line.
A third rail, also known as a live rail, electric rail, or conductor rail, is a method of providing electric power to a train. It is a semi-continuous rigid conductor placed alongside or between the rails of a railway track.
A third rail provides electric traction power to trains using an additional rail (conductor rail) to transfer electric power to the train.
