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    Wire sizes are designated by numbers which correspond to numbers on a standard gauge. Of course wire sizes could be given in thousandths of an inch but it has been found that the use of a certain number to designate a certain size wire simplifies matters a great deal. A standard wire gauge is the B & S Gauge, named after the Brown and Sharp Tool Manufacturing Company. This is sometimes called the “American Wire Gauge.” Details of wire gauges and wire tables will be given in a later lesson text.
    When considering various materials of which conductors and resistors are made, it is customary to talk about their resistance as compared to the resistance of copper. In other words, copper is used as a standard and the resistance of any other metal is given

TABLE NO. 1
ConductorRelative Resistance
(as compared with copper)
Silver0.92
Copper1.00
Aluminum1.67
Zinc3.60
Iron6.17
Nickel7.72
Steel8.62
German Silver17.30

as being so many times that of copper. Of course in doing this we must assume that the metals we are considering are of the same shape, form and size. The wire used for the filament rheostat in Fig. 8 to regulate the amount of current flow in the circuit has many times the resistance of a copper wire, the same size and same length. Considering copper as the starting point, that is, 1, iron wire will have a certain number of times more resistance than copper, as will steel, German silver, and wires of other metals. For example, German silver has 17..3 times as much resistance as copper; an aluminum wire will have 1.67 times as much resistance as copper. A table is given above in which the relative resistances of various metals are given, using copper as the standard.

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Transcriber  Jennifer Ellis