WIRING RULES AND REQUIREMENTS.

The leading-in wires of these flexible cords must be con< nected to heaters or the like at the point of lowest temperature, and where such wires are detachable at the heater, their terminals must be arranged with female ends protected by porcelain extending at least one-eighth inch beyond the metal terminals.

If the connection at the heater is fixed, a separable doublepole connector must be placed in the circuit so that in case an undue strain is brought on the conductors the device will be automatically cut out and disconnected.

Flexible cord connections longer than six feet will not be permitted.

Receptacles for plug attachments must be placed at least six inches above the floor.

Where switches are provided they must conform to the rules laid down in Section 26 of the General Requirements.

Where a number of utensils are grouped for general cooking service, installations to be approved must be provided with slate, soapstone or other approved slab or table for utensils to rest upon. Plug receptacles mounted on slate or other approved material shall be attached to mains running at least six inches above the working surface of the table.

Sad irons and other heating appliances that are intended to be applied to inflammable articles, such as clothing, must be arranged as above as far as connections, etc., are concealed and must also be provided with approved attachments which will cut off current when they are not in actual use.

NATIONAL BOARD FIRE UNDERWRITERS.

The leading-in wires to these forms of apparatus must be connected through porcelain connecting blocks, and the cable or cord of the same must be passed through an insulated elastic spiral or spring so arranged as to protect the same from kinking, chafing or like injury at or near the point of conuection.

These conductors must be so placed that they will at all times be at least four feet from the floor and well protected against contact with water pipes or other possible ground connections.

The use of no flexible cord will be permitted, unless specifically approved by this Board.

WIRING.

Wire Gauges.—In practice sizes of wires or conductors are designated in two ways: first, by measurements in 1,000th of an inch, and, secondly, by the number of circular mils they contain, a circular mil being a circle one one-thousands of an inch in diameter, and the number of these circles contained in a cross section of a piece of wire is called a size of so many circular mils of cross section, or so many circular mils wire, the other being mils diameter. A copper bar one square inch in size, contains 1,273,200 circular mils, and a round wire, one inch in diameter contains exactly one million circular mils.

Wire gauges are employed for accurately measuring the diameter of a wire, this is done so as to calculate the resistance of a given length of such wire.

Fig. 172, page 391, shows a form of wire guage called the round wire gauge. Notches are cut in the edges. Numbers indicating the different sizes of the wire are affixed to each of the openings; the number 5 in the gauge indicates that wire that will just pass through straight sides of the opening is No. 5 wire Brown & Sharp gauge (B. & S. G.)

Fig. 171, page 385, shows the Birmingham wire gauge (B. W. G.) In general electric practice the Brown & Sharp (American) Wire Gauge is used for copper wire and the Birmingham Wire Gauge for iron wire.

The Micrometer Wire Gauge is shown in Fig. 170, page 379. This is a device used for measuring the diameter of a wire in the thousandths of an inch. Micro as a prefix denotes

the millionth part.