of at least six feet, unless otherwise specified.

All poles shall be set perpendicularly on straight-line work. On curves, poles should be set with an outward rake.

The holes shall be dug sufficiently large to admit the butt of the pole without hewing; and after the pole is set, the earth shall be returned and thoroughly tamped around all the base of the pole. Tamping shall be done in the proportion of three tampers to one shoveler. Upon curves the poles must be laterally guyed.

Every eighth pole to be laterally guyed on both sides, and on steep hills every pole shall be head-guyed in both directions.

The two end poles of each line shall be head and laterally guyed. On long spans the poles shall be head-guyed both ways, and side-guyed in both directions.

"Y" guying to be used in all cases.

Where it is difficult to get good setting for a pole, same to be set in "sand-barrel" or concrete, to be approved by the engineers. In cases where poles are set in rock, pole to be hewn to fit an approved iron shoe, which is to be securely bolted to rock. Shoe to be painted inside with two coats of white lead before pole is inserted. Outside of shoe to be smooth, and hydraulic cement to be placed on top of rock on which shoe is set.

Guys to be fastened to poles by means of galvanized eye-bolt, fitted with galvanized washers under head and under nut of bolt.

Placing of Cross-Arms. On straight-line work, the cross-arms to be placed on alternate sides of succeeding poles. On long spans the cross-arms of terminal poles shall be placed opposite the long section. Double cross-arms to be used on all abrupt changes in direction and also on end poles.

At the end of lines the arms of at least the last two poles shall be placed on the side facing the terminal of the line. On curves the cross-arms shall face towards the middle of the curve.

Long spans of 200 feet shall be head-guyed, and if possible side-guyed in both directions.

Tying of Wires. Line wires shall be tied in a manner as approved by the engineers.

Joints. All joints to be made either with a McIntyre sleeve or a Western Union splice, and to be thoroughly soldered, taped, and bound with cord.

Guard Hooks. To be placed on each cross-arm on sharp bends.

Guard Wires.

below another line.

To be placed wherever wires cross above or

Binding Wire. Binding wire to be used to secure wires on all insulators. Wires to be of first-class insulation, solid copper wire, No binding wire

two gauge numbers smaller than the line wire. smaller than No. 8 B and S. gauge to be used.

Excavation. All excavating and filling for pole line to be done by contractor; also felling of trees, bushes, and all blasting, grading, etc. Trees and bushes to be trimmed so that no branch can come in contact with the wires. All removing and replacing of fences or other structures which may be found necessary for locating pole line to be done by the contractor.

CHAPTER XIII.

UNDERGROUND ELECTRICAL CONDUCTORS.

THE branch of electrical light engineering that is the greatest in magnitude, and involves the largest expenditure, is that which relates to the designing, laying, and maintaining of a large system of underground conductors. In no other department of electric lighting are the practice and results so variable. For nearly ten years after electric lighting was first introduced, the distribution of a current was effected almost entirely by overhead wires, the only important exception being the Edison Underground System, first laid in 1882, and generally employed by most of the low-tension, direct-current systems in the larger cities of this country, and in many places abroad. Since 1890 the popular objection to the use of overhead electrical wires has grown, and wherever possible has demanded the substitution for them of underground conductors. The enormous expense of making the change, as well as the almost utter lack of experience with buried high-tension circuits, made this a most formidable problem at first. As is usual in such cases, extraordinary methods were devised for overcoming the apparent difficulties. It has been found, however, that very simple construction, provided it is of good quality, insures the practical success and permanence of underground conductors. In fact, alternating current and arc-lighting circuits of 1000 to 7000 volts. are commonly laid in underground conduits, and do not give much more trouble than low-tension wires, including those employed for telegraphic and telephonic purposes. The essential elements of an underground system of conductors are, first, the conductor itself, which is almost invariably composed of copper; second, the insulation, which may be either a complete covering of non-conducting material, or simply points of support; and third, the mechanical protection, which usually takes the form of a tube or conduit, and must be particularly strong in order to withstand the severe conditions to which it is exposed.

In some instances, especially in Europe, iron-armored cables are laid directly in the earth, without any conduit to protect them. The armor, which is relied upon for mechanical protection, consists of a spiral winding of iron or steel wire, like that of a submarine cable, or a spiral wrapping of iron or steel tape, with overlapping joints. In either case there is a certain amount of flexibility which a conduit does not possess, enabling the cable to pass around obstacles and adapt itself to the various underground pipes, etc., that are often very numerous in large cities. Moreover, the ironarmored cable would occupy much less space than an equivalent conduit. In some underground conductor systems the cables are drawn in after the conduits are built, and in others the conductors are put in the sections before they are laid, or are built in at the same time.

Wrought-Iron or Steel Pipes, similar to gas or steam pipes with screw or other connections, is the strongest and one of the most satisfactory forms of conduit; and it has been extensively adopted,

particularly where its rather high first cost is not a serious objection. Its advantages are great strength to resist the severe strains due to the pressure of the earth, often aggravated by unequal settling. It is also well adapted to withstand blows of pick-axes, shovels, etc., to which conduits are exposed during subsequent excavations of the same ground. Wrought-iron or steel pipes require to be of less thickness, and therefore occupy less space than any other form of conduit. They can be joined by screw or other connections which are most secure, and can also be made water-tight. Such a pipe can be bent to a reasonable extent without breaking or opening the joints; whereas with almost any other form of conduit the unequal settling of the ground, which is almost certain to occur, is likely to crack or break it.

The disadvantages of wrought-iron pipes are their somewhat high first cost, and the fact that they are made of conducting material, which will cause a ground connection if the insulation of the wire is injured. It is doubtful, however, if non-conducting conduits, such as earthenware, are really better for underground construction. If a difficulty occurs in the insulation of the wire, the incidental insulation afforded by the conduit is hardly sufficient to enable the circuit to be worked properly. The moisture which would almost always be present would produce a sufficient "ground" to render it undesirable and probably dangerous to employ the conductor. In most cases it would be just as well, and would enable a fault to be more quickly detected and located, if a “dead ground,” i.e., low-resistance ground connection were made immediately. In fact, with high-tension circuits in non-conducting conduits, it is important to have the lead sheathing of the cables that are ordinarily used well grounded throughout its entire length, otherwise a defect in the insulation, or simply the electrostatic charging and discharging which takes place with alternating currents, render it dangerous to touch the lead sheathing.

Wrought-Iron Pipe in Hydraulic Cement. This is used to quite a large extent, the ordinary construction for this conduit. consisting in digging a trench in the street, the size depending upon the number of pipes to be laid. The bottom of this trench, after being carefully leveled or graded, is covered with a layer of good concrete 2 to 4 inches deep, and the sides are braced with plank. A suitable mixture for this purpose is composed of