Lightning Conductors: Their History, Nature, and Mode of Application

by F.C.S. Richard Anderson

All metallic chimney caps, cornices and railings on the tops of buildings, as well as the water-pipes, gas-pipes, hot water-pipes, and other large or long pieces of metal, whether they occur inside or outside the building, are connected with each other by a conductor composed of light stranded wires, each about three-sixteenths of an inch in diameter; they are also connected with the main conductor at its nearest point. Where several adjacent buildings have each a metallic roof, these roofs are connected together by means of a horizontal conductor.

The terminal rod of the conductor generally projects about four feet above the chimney or other highest point of the building. It consists of a round iron rod seven-sixteenths of an inch in diameter, the lower extremity being hammered out for the purpose of fastening it to the conductor by soldering and screws or by bolts. A small building, not exceeding twenty-five feet in length or breadth, is generally fitted with either one terminal rod placed on the centre of the ridge of the roof, or with two rods, one at each end of the ridge, the latter method being the preferable one. In larger buildings terminal rods are placed at intervals of about twenty feet along the roof. The upper end of the rod is sometimes pointed, but not always, the argument being that although the ordinary end of a rod is blunt when used in connection with a Leyden jar, but that when applied to a thunder-cloud, which extends over thousands of acres, it becomes pointed, and bears the same proportion to a thunder-cloud as the sharp point of a needle does to the hand of a man. Occasionally the point is tipped with platinum, gold, silver, or pure copper, in order to prevent oxidation, but this is not considered essential, it being presumed that, practically no amount of rust on the top would impair the efficacy of the terminal rod.

In the case of a building having a flag-staff upon it, a galvanised iron wire is fastened along it and projects about six inches above the top, the lower end of the wire being of course carefully soldered or otherwise connected with the main conductor.

Steeples and spires, in addition to the ordinary vertical conductor, are fitted with horizontal conductors placed around them at intervals of about twenty feet, and connected with the vertical conductor. This is to provide against the occasional discharges that take place in the centre of steeples, and which are caused by the deflection of the discharge in the air by the rain.

Chimneys and air shafts, from which heated air or smoke escapes, are fitted with metallic caps which are connected with the general conductor. In order to protect this metallic cap from the effects of the sulphurous fumes arising from the chimney, a terra-cotta cap is contrived to fit inside the metallic cap. An analogous method is adopted with regard to the ventilators of barns and ice-houses. If these buildings have the ordinary ventilators in the form of dormer windows upon the roof, an iron rod seven-sixteenths of an inch in diameter is placed vertically across, and above the centre of the opening of each ventilator, and connected with the conductor. Should the barn or ice-house have openings or doors through which warm vapour can escape, a conductor is fixed to the roof at the gable ends above the centre of each opening or door, and extended outwards about five feet, at an angle of forty-five degrees from the roof, so as to be in line with any ascending vapour, or any descending charge of electricity following the course of the vapour. All these auxiliary conductors and terminal rods are metallically connected with the main conductor of the building.

The conductors are simply fastened to the building by iron staples or by straps of sheet iron, pierced with two holes for nails or screws.

In America, as elsewhere, the earth-terminal is regarded as of prime importance, and in all properly constructed lightning conductors receives the greatest care and attention. In the first place, such metal pipes as lead from the building to the water-mains, gas-mains, and sewers are carefully connected with the principal lightning conductor, in order that they may act as auxiliary earth-terminals. For the principal earth-terminal many contrivances have been brought forward, but very few possess any originality, and many are positively useless. Some of the best are similar to those in use in England; among others, perhaps the best method is that of placing a cast or wrought-iron pipe of three inches inside diameter, and about ten feet long, vertically in thoroughly moist earth and carefully connecting the conductor, or conductors, with it. The chief objections to this plan are the occasional difficulty of getting a moist earth at all, and the possibility of earth that is generally moist getting dried up in hot weather. To obviate these risks, the following arrangement is used:—

In a pipe of wrought or cast iron, at least ten feet long, and having an inside diameter of two inches with a thickness of three-eighths of an inch, are made a number of longitudinal openings or perforations, about ten inches long and a quarter of an inch wide. These openings or perforations are made at intervals of ten inches, and are placed in one or two lines opposite to each other. If it is preferred, round holes of from half an inch to one inch in diameter, and about six inches distant from each other, may be substituted for the longitudinal openings. This perforated pipe is placed in an upright position in the earth, and is so situated that it receives at its top opening the waste or rain water flowing along a channel or drain constructed for that purpose. The water, after running into the top of the pipe, gradually percolates down, and passing through the perforations or openings into the earth around and underneath the pipe, moistens it to such an extent and at such a depth as to render it but little affected by the heat of the sun. The pipe is generally placed at some little distance from the building, so as to give a sufficient area of earth to be kept moistened and to prevent the walls of the building being affected by the damp.

Occasionally, the pipe is made triangular or square, and with perforated branches and other metallic conductors. It is also sometimes constructed with enlargements at the top or bottom, so as to hold more water. Probably, however, the simplest plan is the best, as—if the soil be suitable—a plain round wrought-iron pipe can be driven into the earth. If a cast-iron pipe is used, a hole of a convenient size is excavated for it. In this case, great care has to be taken that the earth is thoroughly well rammed down all round the pipe.

Another arrangement is to employ, instead of a cast or wrought-iron pipe, a number of round or flat-iron bars, fastened together at the top and bottom by rivetting to metal hoops in such a manner that intervals are left between each bar, through which the water can pass. Sometimes a solid pipe without the openings is used, but it is not found to be so satisfactory as the perforated pipe, because the latter allows a greater amount of water to pass through it into the soil, thereby furnishing a larger area of moist earth.