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Contrary to the extensive definition used by Chappe, Morse argued that the term telegraph can strictly be applied only to systems that transmit and record messages at a distance. There is no definite record of the system ever being used, but there are several passages in ancient texts that some think are suggestive. One of the few for which details are known is a system invented by Aeneas Tacticus (4th century BC). The earliest true telegraph put into widespread use was the Chappe telegraph, an optical telegraph invented by Claude Chappe in the late 18th century. The word telegraph (from Ancient Greek: τῆλε (têle) 'at a distance' and γράφειν (gráphein) 'to write') was coined by the French inventor of the semaphore telegraph, Claude Chappe, who also coined the word semaphore. The next improvement was the Baudot code of 1874. French engineer Émile Baudot patented a printing telegraph in which the signals were translated automatically into typographic characters.

26-29 Possibly the first alphabetic telegraph code in the modern era is due to Franz Kessler who published his work in 1616. Kessler used a lamp placed inside a barrel with a moveable shutter operated by the signaller. The first widely used system (Wheatstone, 1858) was first put into service with the British General Post Office in 1867. A novel feature of the Wheatstone system was the use of bipolar encoding. Holzmann and Pehrson, for instance, suggest that Livy is describing its use by Philip V of Macedon in 207 BC during the First Macedonian War. Smoke signals, for instance, are to be considered semaphore, not telegraph. While the signalling was complex (for instance, different-coloured flags could be used to indicate enemy strength), only predetermined messages could be sent. A wirephoto or wire picture was a newspaper picture that was sent from a remote location by a facsimile telegraph. This particular concrete pole supports: - Static wire. For overhead cables the fiber is integrated into the core of a phase wire.

A Delta-star (also known as delta - wye or delta Y) transformer is often used for producing a 3 phase, or single phase and neutral supply to homes and industry. This differentiates it from a 3 phase supply which has 3 wires 120 degrees out of phase with each other. Most of the early electrical systems required multiple wires (Ronalds' system was an exception), but the system developed in the United States by Morse and Vail was a single-wire system. The cost of installing wires was ultimately more economically significant than the cost of training operators. The electric telegraph started to replace the optical telegraph in the mid-19th century. The electric telegraph was slower to develop in France due to the established optical telegraph system, but an electrical telegraph was put into use with a code compatible with the Chappe optical telegraph. It is principally used for rural electrification, but also finds use for larger isolated loads such as water pumps.

Tacticus's system had water filled pots at the two signal stations which were drained in synchronisation. Going back to the water analogy, when you stand on a hose, you increase the resistance and restrict the flow. What Is Resistivity and How Does It Affect Resistance? Thus, reducing the current by a factor of two lowers the energy lost to conductor resistance by a factor of four for any given size of conductor. Polybius (2nd century BC) suggested using two successive groups of torches to identify the coordinates of the letter of the alphabet being transmitted. The few remaining telegraph applications were largely taken over by alternatives on the internet towards the end of the 20th century. A fuse that worked loose could end up protruding from the socket, electrically live and posing a shock hazard, when the plug was removed. The larger top pin is the earth connection, the left-hand pin is neutral and the right-hand pin is line when looking at a socket or at the rear of a plug. The power added by any system increases as the line voltage decreases. The voltage rating of the fuse must be equal to or, greater than, what would become the open-circuit voltage.

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