are insulated, and the insulation of the tie-wire should be equal in character and thickness to the line-wire that it ties.

Dead Ending.- When a line ter

minates it is dead-ended by taking a turn around the insulator and wrapping it about itself, or by means of a McIntire connector.

Service Connections and Loops. When it is necessary to take a tap off to give service, an extra insulator must be mounted on the cross-arm, in order that the strain of the service main may not put a side strain on the line-wire; for a series circuit the line is usually dead-ended at the nearest pole, and a loop taken to the building to be served. this case the arrangement shown in Fig. 209 may be used.

In

LINE WIRE

Fig. 208. Method of making Tie.

Limitations of Voltage. The maximum voltage that it is possible to employ on overhead lines depends upon conditions. In 1890 a pressure of 5000 volts was considered to be very high, but gradu

ally the apparatus and methods have been improved until 40,000 or even 60,000 volts is now regarded as commercially practicable.

The electrical maintenance of such a circuit depends entirely upon the insulators, since the wires are usually bare, and the poles even if made of wood should never be depended upon for insulation, especially at such high voltages.

In a paper before the American Institute of Electrical Engineers,* Mr. C. F. Scott gave the results of experiments on several lines, and pointed out that the loss between wires by leakage directly through the air rose rapidly above a certain voltage. In Fig. 210, which shows some of these data, it will be noted (curve 1) that the loss between two No. 28 wires 48 inches apart was 500 watts at

30,000 volts, each wire being 1040 feet long. This is far too great for commercial work, since the waste would amount to about 2.5 k.w. per mile. With larger wires the loss decreases; for example, in curve 3 the leakage for two No. 8 wires the same distance apart is only one-fifth as great at 30,000 volts, being 100 watts for the same length. When No. 7 wires, rubber-covered, are used (curve 4), the loss is practically nil at 30,000 volts, and only becomes 50 watts at 60,000 volts, or .25 k.w. per mile. The substitution of still

larger conductors secures a further reduction in this leakage through the air, so that it can be kept within reasonable limits event at 60,000 volts. A transmission line in California, which is designed to operate at this pressure, employs aluminum wires one inch in diameter, which should give very little air leakage, even though they are bare. When the distance between wires is increased, the loss is diminished, as shown in Fig. 211. It is also a fact that the leakage depends upon the wave form of the pressure, being greater with peaked than with flat topped waves, since the maximum volt

*Transactions, June 30, 1898.

age is higher in the former case. The percentage of humidity in the atmosphere, or even a fall of rain or snow, does not materially increase this loss through the air.

Lightning Arresters are required in almost all cases in connection. with overhead conductors. The principal forms in use, and the manner of using them, were described quite fully in Vol. I., pages 425 to 438.

GENERAL SPECIFICATIONS FOR ORDINARY POLE LINE

CONSTRUCTION.

(2000 VOLTS.)

Poles to be of best quality cedar or chestnut, round or octagonal, as specified. Height to be approximately thirty (30) to thirty-five (35) feet. Diameter of base to be ten (10) inches. Diameter of top to be about six (6) inches. The poles to be straight and knots closely trimmed. Tops to be chamfered.

Gains to be cut square with the axis of the pole and with all other gains, and to be accurately made to fit cross-arms, so as to bring the cross-arms nearly flush with the pole.

Painting. Poles which are specified to be painted to have the lower six and one-half (64) feet, including the base of the pole, either creosoted or painted with a heavy coat of tar paint or equal. (This is not to be done if the pole is "green" or sappy.) The roof of the

pole to be painted with three (3) coats of best quality white lead. · All gains to receive two (2) coats of best white lead previous to the introduction of cross-arms. Lower shanks of pins to be painted with white lead before being inserted into cross-arms. Cross-arms to be thoroughly painted with two (2) good coats of mineral paint put on with a brush. After the poles are erected and wires in place all the poles specified to be painted with two (2) coats of best quality dark-green mineral paint.

Guy-Stubs and Anchor Logs to be used where the pole needs side guying on a sharp bend, or wherever the country does not provide a more convenient way to guy them. These anchor logs or guy-stubs to be of proper dimensions, depending on the size of the pole and weight of the line.

Cross-Arms to be thoroughly sound, straight-grained timber, of southern pine, and free from knots. The arms to be of requisite length, to be sawed true and square, and up to the dimensions specified. The top side of the cross-arm to be chamfered throughout the whole length, with the exception of eight (8) inches at the center, where the arm fits the gain. Cross-arms to have holes bored of spacing and size for pins, as specified or shown on drawings. Cross-arms to be screwed to the pole by two (2) inch galvanized iron bolts extending entirely through the arm and pole. Under the head and nut of each bolt a galvanized iron washer, not less than 24 inches in diameter, shall be placed. Bolts to be staggered. (This construction refers to cross-arms carrying heavy wires and large number of same. On light lines lag screws are sufficient.)

Iron Fittings to be of good quality best refined wrought iron, which would conform to good bridge specifications, to be thoroughly galvanized. Galvanizing to be subject to a test. Crossarm braces to be used on all the cross-arms having four (4) or more pins. The braces to be secured to the pole with a lag screw, and to the cross-arm with carriage bolts of sufficient length to go through the braces and arms. Galvanized iron washers to be placed under the head of all bolts, nuts, and lag screws.

Pins. All pins to be best quality, sound, clear, split locust, free from knots and sapwood. Pins to be of standard dimensions, which are governed by the size and weight of the insulators, etc. The threading and tapering shall be neatly and accurately cut,

showing the full thread, and shall accurately fit the insulator. Each pin to be secured to the cross-arm by a sixpenny galvanized iron wire nail driven straight through cross-arm and shank of pin. On all curves pins to be bolted by galvanized iron bolts.

Insulators. Insulators as per sample to be used, to be sound, strong, free from fins, having threaded holes accurately molded and of uniform size. To be double petticoated, made of glass, and subject to a break-down test of 6000 volts, from a source capable of delivering five (5) amperes at that pressure.

Guy-Rods. Anchor guys shall be attached to galvanized iron guy-rods. These rods to be from 6 to 8 feet long, g inch in diameter, provided with a galvanized iron washer inch thick and 3 inches square, with 3 inch hole for reception of the rod.

Wire-Rope Fittings. All wire-rope fittings, such as thimbles, guy-clamps, rings, sockets, shall be of first-class quality of wirerope fittings, equivalent in every respect to those manufactured by the Roebling Company or Washburn & Moen. To be galvanized.

Lightning Rods. Every tenth pole to be supplied with a lightning rod made of No. 6 galvanized iron wire, carried at least one foot above top of pole, and secured to same by heavy galvanized steel staples made of No. 4 (B. and S. gauge) wire. These staples shall be 24 inches long. The wire shall be carried down the pole, and thoroughly buried in the ground at the base of the pole, with at least two hand turns.

Guy-Ropes to be made of good flexible quality galvanized iron, and to be composed of one or more strands, depending on the stress to be borne by the guy. To conform to good specifications for elongation, twist, and breaking.

Construction Details. The line shall be located by measuring off and placing stakes for pole location at distances of 120 feet as an average. Such stakes must be placed as nearly in line as possible. In case of obstacles, the pole should be located as near the stakes as possible. In the distribution of the poles, the strongest and heaviest poles shall be placed on line corners, while the bestlooking shall be distributed throughout the town, or in the front of residences. The length of the pole shall be proportioned to the contour of the country, so that the wires may be strung without abrupt changes in level.

On straight lines all poles shall be set in the ground to a depth