A modern convenience often taken for granted, electric power, can be found everywhere. To route electricity from the power station to your wall outlet requires many steps. Residential house wiring includes a variety of wiring and control devices to ensure safe and reliable service.
Electricity in the home is distributed by means of branch circuits. Furthermore, each branch circuit is supplied via a circuit breaker sized per the expected load on the circuit. A typical lighting and receptacle circuit will be rated at 15A. Because of their size, larger loads like ovens, clothes dryers, and air conditioning units are given dedicated circuit breakers.
A typical home can have dozens of 15A circuits, and several 20A, 30A, or even 50A circuits. Yet the total of all these breakers is much more than the size of the main breaker. However, this is intentional. It’s highly unlikely that every circuit will be fully loaded at any one time, so a demand factor is taken into account to keep the main breaker at a reasonable size.
A wood-framed home will typically use solid copper non-metallic sheathed cable for the majority of wiring applications. Solid conductors are easy to terminate and cheaper than equivalent stranded wire. The AWG size of the wire is determined by the expected load on the circuit and by the size of the breaker protecting it. You should never connect a wire to a breaker that is too large to protect it, as an overloaded wire can easily catch fire.