Communications cables are usually supported by steel strand. Incredibly, EV policies now have to cover customers for trips or falls on their own charging cables. In the 1980s and 1990s 12 kV DC was being tested on the October Railway near Leningrad (now Petersburg). Historically, concerns of resource independence have played a role in the decision to electrify railway lines. Historically, transmission and distribution lines were often owned by the same company, but starting in the 1990s, many countries liberalized the regulation of the electricity market in ways that led to separate companies handling transmission and distribution. These effects are often undesirable, in the first case amounting to unwanted transmission of energy which may adversely affect nearby equipment or other parts of the same piece of equipment; and in the second case, unwanted pickup of noise which may mask the desired signal being carried by the cable, or, if the cable is carrying power supply or control voltages, pollute them to such an extent as to cause equipment malfunction. Different regions may use different supply voltages and frequencies, complicating through service and requiring greater complexity of locomotive power. DC rolling stock was equipped with ignitron-based converters to lower the supply voltage to 3 kV.

In addition to the lack of grounding, these obsolete receptacles could allow a connected device to overheat and create a fire hazard if a device designed for the wrong voltage is connected. Disadvantages of electric traction include: high capital costs that may be uneconomic on lightly trafficked routes, a relative lack of flexibility (since electric trains need third rails or overhead wires), and a vulnerability to power interruptions. Some of these are independent of the contact system used, so that, for example, 750 V DC may be used with either third rail or overhead lines. Portable appliances with metal cases also have a bonding conductor in the flexible cable and plug connecting them to the distribution system. This pole supports: - Three-phase primary electric distribution. Most electrification systems use overhead wires, but third rail is an option up to 1,500 V. Third rail systems almost exclusively use DC distribution. Third rail is more compact than overhead wires and can be used in smaller-diameter tunnels, an important factor for subway systems. The same system was used for Milan's earliest underground line, Milan Metro's line 1, whose more recent lines use an overhead catenary or a third rail.

Between 2012 and 2016, the electrification was converted to 25 kV 50 Hz, which is the countrywide system. The system was also used for suburban electrification in East London and Manchester, now converted to 25 kV AC. In 1970 the Ural Electromechanical Institute of Railway Engineers carried out calculations for railway electrification at 12 kV DC, showing that the equivalent loss levels for a 25 kV AC system could be achieved with DC voltage between 11 and 16 kV. DC voltages between 600 V and 750 V are used by most tramways and trolleybus networks, as well as some metro systems as the traction motors accept this voltage without the weight of an on-board transformer. The history of railway electrification dates back to the late 19th century when the first electric tramways were introduced in cities like Berlin, London, and New York City. Railway electrification has constantly increased in the past decades, and as of 2022, electrified tracks account for nearly one-third of total tracks globally.

Therefore, most long-distance lines in developing or sparsely populated countries are not electrified due to relatively low frequency of trains. In the United Kingdom, 1,500 V DC was used in 1954 for the Woodhead trans-Pennine route (now closed); the system used regenerative braking, allowing for transfer of energy between climbing and descending trains on the steep approaches to the tunnel. Some electric traction systems provide regenerative braking that turns the train's kinetic energy back into electricity and returns it to the supply system to be used by other trains or the general utility grid. These take into account the number of trains drawing current and their distance from the substation. The early electrification of railways used direct current (DC) power systems, which were limited in terms of the distance they could transmit power. In the United States, the New York, New Haven and Hartford Railroad was one of the first major railways to be electrified.

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