then be soldered, to insure preservation, and covered with an insulation equal to that on the conductors.

[Section f. All joints must be soldered, even if made with the McIntyre or any other patent splicing device. This ruling applies to joints and splices in all classes of wiring covered by these rules.]

g. Telegraph, telephone, and similar wires must not be placed on the same cross-arm with electric light or power wires.

11. Service-blocks:

Must be covered over their entire surface with at least two coats of waterproof paint.

FIG. 28.

Showing Guard-iron. FIG. 29.-Petticoat Insulator. FIG. 30. - Rubber Hook. FIG. 31.-Twisted Joint. FIG. 32.-Service-block. FIG. 33.-Cross-arms.

The "petticoat-insulator" has a petticoat, or lip, round the bottom. (Fig. 29.) There may be leakage over wet surfaces, but with the petticoat insulator the

inside surface of the petticoat is protected from the weather and is always dry. Thus the current cannot leak from the wire to the ground since it would have to cross this dry surface in order to reach the wooden pin on which the insulator is screwed, and this pin affords the only path to the earth.

Figure 12 shows a "porcelain knob." Dry porcelain is one of the best of insulators, but the knob has all its surface exposed to the weather, and when wet there may be considerable leakage over this surface. Porcelain also sometimes absorbs moisture.

The "porcelain cleat" (Fig. 11) and the "rubber hook" (Fig. 30) are objectionable for outside work, for the same reason that knobs are objectionable.

Figure 31 shows a "twisted joint" that will be secure without solder and that will insure good electrical connection. If left simply twisted in this way, or even if covered, the copper would soon become tarnished with a thin layer of poorly conducting substance. This would impair the connection and introduce into the circuit a certain amount of resistance that would perhaps be the cause of considerable heating. To make a permanently good joint, it is necessary to solder it thoroughly.

"Service-blocks" are the blocks of wood to which the insulators holding the service-wires are attached. The object of the waterproof paint is simply to give a safe

guard against the absorption of moisture by the wood, which would make it a conductor and thus increase the liability of leakage. (Fig. 32.)

There is, of course, more liability of accidental contact between wires where they are near together, as they would be when attached to the same cross-arm. There is also more liability of a connection between the two circuits on account of leakage through a wet cross-arm. Only low electrical pressures are required to operate telephone, telegraph, and similar circuits, and since less care is usually taken with their insulation, even slight leakages to them, of light or power currents, might prove dangerous.

It will be observed that most of the provisions in Rules 10 and 11 are made for the purpose of securing good insulation. Wires and supports out of doors are, of course, often exposed to thorough soaking, and wind storms bring strains upon the supports, swing wires out of position and rub them against awning frames, cornices, etc., so that the greatest precaution must be taken if the insulation of the circuit is to be at all times preserved.

A proper insulating covering on the wire will prevent leakage as long as the covering is in its original condition. It is a protection against leakage that comes from accidental contacts with conducting material, and prevents much of the trouble that arises with inferior

coverings. When, however, the covering rubs against stonework or other substances, as it often does when the wire is moved by the wind, the covering is soon abraded so that the bare wire is exposed to contact. Thus, though the insulating covering gives security in many cases, it cannot be depended upon exclusively, and precautions must be taken against contacts with any foreign substances and also against the possibility that dampness will cause leakage at some point where the covering has been injured.

(HIGH-POTENTIAL SYSTEMS.)

INTERIOR CONDUCTORS.

12. All Interior Conductors:

a. Must be covered where they enter buildings from outside terminal insulators to and through the walls, with extra waterproof insulation, and must have drip-loops outside. The hole through which the conductor passes must be bushed with waterproof and non-combustible insulating tube, slanting upward toward the inside. The tube must be sealed with tape, thoroughly painted, and securing the tube to the wire.

b. Must be arranged to enter and leave the building through a double contact service-switch, which will effectually close the main circuit and disconnect the interior wires when it is turned "off." The switch must be so constructed that it shall be automatic in its action, not stopping between points when started, and prevent an arc between the points under all circumstances; it must indi

cate on inspection whether the current be "on" or "off," and be mounted in a non-combustible case, and kept free from moisture, and easy of access to police or firemen. So-called "snap-switches" shall not be used on high-potential circuits.

c. Must be always in plain sight, and never encased, except when required by the Inspector.

d. Must be covered in all cases with an approved noncombustible material that will adhere to the wire, not fray by friction, and bear a temperature of 150 degrees Fahr., without softening.

[Section d. Insulation that will be approved for interior conductors must be solid, at least three sixty-fourths of an inch in thickness, and covered with a substantial braid. It must not readily carry fire, must show an insulating resistance of one megohm per mile after two weeks' submersion in water at 70 degrees Fahr., and three days' submersion in lime-water, with a current of 550 volts, and after three minutes' electrification.]

[See List of Wires, page 80.]

e. Must be supported on glass or porcelain insulators, and kept rigidly at least eight inches from each other, except within the structure of lamps or on hanger-boards, cut-out boxes, or the like, where less distance is necessary.

f. Must be separated from contact with walls, floors, timbers or partitions through which they may pass, by noncombustible insulating tube.

g. Must be so spliced or joined as to be both mechanically and electrically secure without solder. They must then be