Electricity requires a complete circuit, to return current to its point of origin or to the ground. That is why household wiring has three copper wires, two of them insulated, usually encased in a single plastic shield. A wire with black insulation carries current --- is "hot." A wire with white insulation is "neutral," and returns current to its origin. A bare wire is the ground, which deflects current to the ground if the circuit is interrupted.
Ohms, Amps, Volts, Watts Measure Electricity
Electricity is the flow of electrons through some conductor. Different materials have different conductivity; copper is best. The resistance to the flow of electrons is measured in ohms. The amount of electricity in a circuit is measured in amperes or amps. The force required to move electricity is called volts. How much electricity is used at the end point is called watts. One watt is the force of 1 amp pushed by 1 volt through a resistance of 1 ohm. Never work on electrical circuits unless they are completely dead, with no current flowing.
Conductors and Insulators
Electrical circuits use conductors, semiconductors, variable resistors and insulators. Conductors allow current to flow freely. Semi-conductors allow current to flow under certain conditions but block it at others. Resistors impede the flow of current in some defined conditions. Insulators block the flow of all current. Most home wiring involves conductors and insulators; semiconductors and resistors are used in electronic equipment and other devices.
Breakers and Fuses
Circuits used in most households have a point of origin, where power from the utility service enters the house. This is marked by a breaker panel or fuse box; they perform the same function, to interrupt the flow of current if there is a circuit problem. Fuses, the older protector, use thin wires which burn in two if the current is excessive or altered. Circuit breakers simply trip a switch to block the current if there is a problem. There also will be a ground, a copper rod driven deep into the ground near the entry box and wired to it.
110 Is Standard Voltage
Most household circuits are called 110-volt, although the flow of power in is usually 115 or 120 volts. The power grid supplying service varies from 110 to 130 volts, so the 110 is a minimum. Some circuits, for large appliances, are 220 volts (although service actually is 240 or 250); these have four wires, two of them hot with a single neutral or "common" return.
Wiring a Plug
The most basic household electrical project is wiring a plug. A receptacle has two plug points, each with two vertical blades (the one on the left slightly larger) and a rounded one below. The larger blade is hot, the smaller neutral and the rounded one the ground. The hot wire attaches to a brass screw on the receptacle, the neutral to a silver screw and the bare ground to a green screw. There are two sets of brass and silver screws but only one set is used for the plug; the second pair is to an extension if the plug is in a series.
Wiring Fixtures and Switches
Ceiling and wall light fixtures are wired much like plugs. Fixtures will have brass, silver and green screws which are connected to the appropriate wires. A switch will wire differently. It will involve two hot wires, one feeding the current into the switch, the other connecting to the fixture or outlet being controlled. Two black wires attach to brass screws, the neutral wire to a silver or dark screw, a ground to the green screw. All fixtures and switches must be grounded.