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Adverse weather conditions, such as high winds and low temperatures, interrupt transmission. These included single phase AC systems, poly-phase AC systems, low voltage incandescent lighting, high-voltage arc lighting, and existing DC motors in factories and street cars. Different classes of loads (for example, lighting, fixed motors, and traction/railway systems) required different voltages, and so used different generators and circuits. This restricted the distance between generating plant and loads. Reliability was improved and capital costs were reduced, because stand-by generating capacity could be shared over many more customers and a wider area. Large cable companies used addressable descramblers to limit access to premium channels for customers not subscribing to higher tiers, however the above magazines often published workarounds for that technology as well. At the optical node, the optical signal is translated back into an electrical signal and carried by coaxial cable distribution lines on utility poles, from which cables branch out to a series of signal amplifiers and line extenders. Transmission companies determine the maximum reliable capacity of each line (ordinarily less than its physical or thermal limit) to ensure that spare capacity is available in the event of a failure in another part of the network. HVDC links stabilize power distribution networks where sudden new loads, or blackouts, in one part of a network might otherwise result in synchronization problems and cascading failures.

The US Northeast faced blackouts in 1965, 1977, 2003, and major blackouts in other US regions in 1996 and 2011. Electric transmission networks are interconnected into regional, national, and even continent-wide networks to reduce the risk of such a failure by providing multiple redundant, alternative routes for power to flow should such shutdowns occur. The optimum size of a conductor for a given voltage and current can be estimated by Kelvin's law for conductor size, which states that size is optimal when the annual cost of energy wasted in resistance is equal to the annual capital charges of providing the conductor. And since conductance is proportional to cross-sectional area, resistive power loss is only reduced proportionally with increasing cross-sectional area, providing a much smaller benefit than the squared reduction provided by multiplying the voltage. The rate of transmission expansion needs to double to support ongoing electrification and reach emission reduction targets. Most North American transmission lines are high-voltage three-phase AC, although single phase AC is sometimes used in railway electrification systems.

5. For dwelling units, conductors, as listed below, shall be permitted as 120/240 volt, 3 wire, single phase service-entrance conductors, service lateral conductors and feeder conductors that serve as the main power feeder to a dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. Tight lays during stranding makes the cable extensible (CBA - as in telephone handset cords). There are also usually upstream channels on the cable to send data from the customer box to the cable headend, for advanced features such as requesting pay-per-view shows or movies, cable internet access, and cable telephone service. Due to widespread cable theft in earlier analog systems, the signals are typically encrypted on modern digital cable systems, and the set-top box must be activated by an activation code sent by the cable company before it will function, which is only sent after the subscriber signs up. Since some readers request historical data on electrical code provisions, we note that the data in this article has been excerpted / adapted from the U.S. National Electrical Code. The locations of wiring size vs ampacity ratings changed in the 2011 NEC and again in the 2014 NEC.

Informational Note No. 1: It is possible that the conductor ampacity will require other correction or adjustment factors applicable to the conductor installation. The conductor material is nearly always an aluminum alloy, formed of several strands and possibly reinforced with steel strands. Since power lines are designed for long-term use, Kelvin's law is used in conjunction with long-term estimates of the price of copper and aluminum as well as interest rates. Copper was sometimes used for overhead transmission, but aluminum is lighter, reduces yields only marginally and costs much less. The reduced current reduces heating losses. Transmitting electricity at high voltage reduces the fraction of energy lost to Joule heating, which varies by conductor type, the current, and the transmission distance. The first long distance AC line was 34 kilometres (21 miles) long, built for the 1884 International Exhibition of Electricity in Turin, Italy. The first three-phase alternating current using high voltage took place in 1891 during the international electricity exhibition in Frankfurt. High-voltage direct current (HVDC) systems require relatively costly conversion equipment that may be economically justified for particular projects such as submarine cables and longer distance high capacity point-to-point transmission. Fault-sensing protective relays at each end of the line must communicate to monitor the flow of power so that faulted conductors or equipment can be quickly de-energized and the balance of the system restored.

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