Single wire is used for the incoming line of the distribution box
Live (L) Wire Connection: In a distribution box setup, the incoming live wire (also known as phase or hot wire, denoted as L or Line) connects to the line terminal of the circuit breaker. In a single-line electrical diagram, each transmission or distribution power line appears as a single line on the page, rather than as three (or four) lines showing individual conductors in a three-phase AC circuit. This condenses the space and complexity of the diagram for simpler troubleshooting. In India, a 230V single-phase AC supply is used for domestic so here all the devices used in the DB is operating with a 230V AC supply whereas in USA 110 or 120V AC supply is used for. Basically, they are simplified and digest picture of whole switchboard, showing only major power equipment and connections to other. Red boxes represent circuit breakers, grey lines represent three-phase bus and interconnecting conductors, the orange circle represents an electric generator, the green spiral is an inductor, and the three overlapping blue circles represent a double-wound transformer with a tertiary winding.
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