A circuit is a continuous closed path along which electricity flows from the source of power, through a device, and back to the source.
The hot wire brings electricity to a device, and the neutral wire returns electricity to the service panel.
The individual fixtures or receptacles on a circuit are connected by either parallel or series wiring. Switches may or may not be added along the way.
In real life, light fixtures, receptacles, and switches are mounted in housing boxes, which also contain and protect all wiring connections.
Numerous routing options exist. When wiring a switch circuit, for example, the cable may run through the switch box and on to the light, or it may run through the light, with a separate "switch loop" running to the switch.
 Additional wires may also pass through one or both boxes, unswitched, on their way to other devices.
Parallel wiring
In most homes, several light fixtures or receptacles operate on the same circuit with the hot and neutral wires running together from one housing box to another; wires to individual devices branch off from them.
Switch wiring
Switches turn things on and off by controlling the flow of electric current. Switches are installed only on hot wires.
The simple knife-blade switch shown at top right in the Switch Wiring illustrations shows how a switch closes (completes) a circuit, turning the light on. When the switch is open, it disconnects the light from the hot bus bar, as shown in the illustration at bottom right.
Series wiring
This type of circuit passes the hot wire through a series of devices before joining the neutral wire that returns to the source.
 Series wiring is rarely used for home light circuits because when one light bulb fails, all the lights go out in the circuit.
A string of old-style Christmas tree lights is an example of series wiring.
Complete Home Wiring
Electricity provides us with comfort and conveniences that we often take for granted until something goes wrong. Fortunately for the do-it-yourselfer, electrical work is one of the easiest kinds of home improvement and repair.
Copyright Sunset Publishing Corporation
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