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The archetype of this category was the Morse system and the code associated with it, both invented by Samuel Morse in 1838. In 1865, the Morse system became the standard for international communication, using a modified form of Morse's code that had been developed for German railways. This was well understood in the late 19th Century and was one of the reasons why London’s Underground railways adopted a fully insulated DC system with a separate negative return rail as well as a positive rail - the four-rail system. Wire types for North American wiring practices are defined by standards issued by Underwriters Laboratories, the Canadian Standards Association, the American Society for Testing and Materials, the National Electrical Manufacturers Association, and the Insulated Cable Engineers Association. Lighting and power receptacle circuits in North American systems are typically radial from a distribution panel containing circuit breakers to protect each branch circuit. Several other types of wiring systems are used for building wiring in the United States; these include corrugated metal armored cable, mineral-insulated cable, other types of power cable, and various types of electrical conduit. Since the early 1960s, wiring in new construction has required a separate grounding conductor used to bond (electrically connect) all normally non-current carrying parts of an electrical installation.

An extended specification, THWN-2 permits use in wet locations and conductor temperatures up to 90°C simultaneously. Other exceptions to the use of BS 1363 plugs and sockets include equipment requiring more than 13 A, low-power portable equipment (such as shavers and toothbrushes) and mains-operated clocks. Digital Museum of Plugs and Sockets. Britain pre-war had used a combination of 2A, 5A, and 15A round pin sockets. In commercial and industrial, unenclosed NM cable is often prohibited in certain areas or altogether (depending on what the building is used for and local/state building codes). The Canadian Electrical Code, while developed independently from the NFPA code, is similar in scope and intent to the US NEC, with only minor variations in technical requirement details; harmonization of the CEC and NEC codes is intended to facilitate free trade between the two countries. It's called a loop because the two wires, connected at one end by the switch and at the other end by your phone, what is electric cable allow current to flow all the way around. Many electrical telegraph systems were invented that operated in different ways, but the ones that became widespread fit into two broad categories.

Beginning in 1850, submarine telegraph cables allowed for the first rapid communication between people on different continents. First are the needle telegraphs, in which electric current sent down the telegraph line produces electromagnetic force to move a needle-shaped pointer into position over a printed list. It was the first electrical telecommunications system and the most widely used of a number of early messaging systems called telegraphs, that were devised to send text messages more quickly than physically carrying them. Only 12 customers across America could see the first color TV broadcast. Electrical telegraphy can be considered the first example of electrical engineering. The rise of the Internet and email in the 1990s largely made dedicated telegraphy networks obsolete. Increasing use of the telephone pushed telegraphy into only a few specialist uses; its use by the general public dwindled to greetings for special occasions. If the length of the wire is small, a few hundred meters to several kilometers, speeds of several megabits per second can be achieved without unacceptable error rate.

This made higher speeds problematic, because the stern of a propeller powered boat comes to lay deeper in the water as speed goes up. Circuits with larger currents (such as for electric furnaces, water heaters, air conditioners, or sub-mains to additional circuit panels) will have larger conductors. Often, 20 ampere circuits are used for general purpose receptacles and lighting. In commercial construction, three-phase circuits are often used. This is a specification for PVC insulation (other thermoplastics are permitted, but rarely used) with a nylon jacket for abrasion resistance. Rigid may be required for certain areas and additionally, vapor-lock fittings may be required in areas where a fire or explosion hazard is present (such as gas stations, chemical factories, grain silos, etc.) PVC can be used where wire is run underground or where concrete will be poured. A duct bank is usually made of multiple PVC conduits encased in concrete. Early needle telegraph models used multiple needles, thus requiring multiple wires to be installed between stations. This was built around the signalling block system in which signal boxes along the line communicate with neighbouring boxes by telegraphic sounding of single-stroke bells and three-position needle telegraph instruments. In 1753, an anonymous writer in the Scots Magazine suggested an electrostatic telegraph.