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It also precludes "crossing" a wall by drawing the solution line up to a wall, perhaps along it, but then leaving the wall on the same side. There are 16 "walls", seven separating rooms and nine separating the rooms from the area outside the drawing. The method of proof is proof by contradiction. That is, we proceed as if a solution exists and ...
For electric power supply, a cable is run either overhead or underground into a distribution board in the home. A distribution board, or circuit breaker panel, is typically a metal box mounted on a wall of the home. In many new homes, the electrical switchboard is located on the outside of the external wall of the garage.
Proof without words: One house is temporarily deleted. The lines connecting the remaining houses with the utilities divide the plane into three regions. Whichever region the deleted house is placed into, the similarly shaded utility is outside the region. By the Jordan curve theorem, a line connecting them must intersect one of the existing lines.
Ceramic bushings protected each wire entering a metal device box, when such an enclosure was used. Loom, a woven flexible insulating sleeve, was slipped over insulated wire to provide additional protection whenever a wire passed over or under another wire, when a wire entered a metal device enclosure, and in other situations prescribed by code.
A similar, usually wall mounted, container used mainly to accommodate switches, sockets and the associated connecting wiring is called a pattress. The term junction box may also be used for a larger item, such as a piece of street furniture. In the UK, such items are often called a cabinet. See Enclosure (electrical).
The neutral is connected to the center tap of the power company transformer of a split-phase system, or the center of the wye connection of a polyphase power system. United States electrical codes require that the neutral be connected to earth at the "service panel" only and at no other point within the building wiring system.
Installing electrical wiring by "chasing" grooves into the masonry structure of the walls of a building. Materials for wiring interior electrical systems in buildings vary depending on: Intended use and amount of power demand on the circuit; Type of occupancy and size of the building; National and local regulations
Couplings connect two pieces of conduit together. Sometimes the fittings are considered sufficiently conductive to bond (electrically unite) the metal conduit to a metal junction box (thus sharing the box's ground connection); other times, grounding bushings are used which have bonding jumpers from the bushing to a grounding screw on the box. [13]