Covered wire for carrying electricity is made in a great variety of forms and designated by names that have been suggested by their use. These wires are made of a single strand or in cables, where several wires are collected, insulated and formed into a single piece. Cables may contain any number of insulated wires.

The sizes of wires are determined by a wire gage. In the United States the B. & S. gage is used as the standard for all wires and sheet metal. The gage originated with the Brown & Sharp Mfg. Co. of Providence, R. I., and has become a national standard by common consent. The numbers range from No. 0000 to No. 60. The size of wire for household electrical service ranges from No. 18 which is 0.04 inch in diameter to No. 8 which is 0.128 inch across. The carrying capacities in amperes of wires, as given by the Underwriters' table of sizes from No. 8 to No. 18, are as.follows:

Wire gage No.

Rubber insulation, amperes

Other insulation, amperes

8

35

50

10

25

30

12

20

25

Wire gage

No.

Rubber insulation, amperes

Other insulation, amperes

14

15

20

16

6

10

18

3

5