Wires for electrical purposes are called conductors, simply because they conduct electricity. Actually, wire is a misnomer, because you don't buy bare metal. Rather the wire -- the metal -- comes covered with insulation, usually plastic. The conductor may consist of either solid metal or twisted strands; solid conductors are used in most house wiring, while the stranded conductors are used in conduit wiring and other applications where flexibility is important.
Conductors are always copper (at one time aluminum was used, but this was found to be a safety hazard).
Wire is commonly spoken of in terms of a number, or gauge, that refers to the diameter of the wire. The larger the number, the smaller the wire. No. 38 wire, for example, is a little thicker than a human hair; No. 18 wire is about the diameter of the head of a pin; No.2 wire has the diameter of a lead pencil. And it keeps getting bigger, with the number designations changing to 1/0, 2/0, 3/0, 4/0, and so forth.
The bigger the wire, the more current it can carry. You will normally be concerned with relatively few wires. Those commonly used in house wiring are numbers 14 and 12; numbers 18 and 16 are common for extension cords; number 14 is used for heavy-duty appliance cords.
Insulated wire is also classified by letter according to type of covering or insulation used, but these designations normally need not concern the do-it-yourselfer.
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