What is a 4th rail?
In concept, ‘fourth rail’ provides vehicle power through two parallel, wayside side-contact, aluminum/stainless steel conductor rails having opposite polarity; hence eliminating the need for running rails to act as part of the power electrification circuit.
What is the voltage of the 4th rail?
630 V DC
Two standard gauge rails are the running rails; the outer third rail carries positive current at +420 V DC and the inner fourth rail is the negative return at –210 V DC, giving a supply voltage of 630 V DC.
What Does touching the third rail mean?
Touching a third rail can result in electrocution, so usage of the metaphor in political situations relates to the risk of “political suicide” that a person would face by raising certain taboo subjects or having points of view that are either censored, shunned or considered highly controversial or offensive to advocate …
Why does the tube have 4 rails?
The fourth rail was chosen, partly as a cheaper option and partly for signalling reasons. As direct current track circuits were to be used to control signals, an insulated return system for the traction current was an effective way of separating the two systems.
What is 3rd or 4th rail?
In 3rd rail systems, the current returns to the supply though the ordinary running rail(s). In a 4th rail system, a second insulated rail is provided, and current return is via a second set of pickup shoes through to the second insulated rail.
Are trains AC or DC?
Direct current, either directly supplied, or converted from AC onboard a train, is the most commonly used. This is because, according to railsystem.net, “DC consumes less energy compared to an AC unit for operating the same service conditions.
Has anyone ever survived the 3rd rail?
Andy Morris hit an electrified third rail after being shoved onto tracks during a drunken fight. A down-on-his-luck construction worker survived a 625-volt zap to the head after getting pushed onto an electrified third rail during a drunken brawl in Brooklyn.
What is Kolkata underground railway called?
Kolkata Metro
The Kolkata Metro (Bengali: কলকাতা মেট্রো) is a rapid transit system serving the city of Kolkata in West Bengal, India.
Why does the London Underground use four rail system?
The London Underground uses the four rail system for two main reasons. Firstly, it was originally required by the government to limit the voltage drop along the line to 7 volts. This was intended to reduce problems caused by stray currents causing electrolysis affecting utility pipes and cables.
Where does power conversion take place on a railway?
Power conversion for a DC system takes place mainly in a railway substation where large, heavy, and more efficient hardware can be used as compared to an AC system where conversion takes place aboard the locomotive where space is limited and losses are significantly higher.
Where are the positive and negative rails on a train?
The positive rail is at a potential of 420 volts above earth and the negative rail at 210 volts below earth. In this view above of Surrey Quays (East London Line) the arrangement of current rails is clearly seen. The negative rail is mounted centrally between the two running rails. The positive rail is mounted outside the running rails.
Where did the steel for the Forth Bridge come from?
The original design required 42,000 tonnes (41,000 long tons; 46,000 short tons) for the cantilevers only, of which 12,000 tonnes (12,000 long tons; 13,000 short tons) was to come from Siemens’ steel works in Landore, Wales and the remainder from the Steel Company of Scotland’s works near Glasgow.