Lightning Rod Conference. Various
screwed end of the conductor. Or a solid copper rod ½ inch diameter [A. 0·20 in.], or wrought iron rod 1 inch diameter [A. 0·79 in.] (where iron conductors are used) the rod in either case forged to a blunt point, and screwed at the lower end, like the tube first described, to fit the coupling.
2. (a). Copper wire rope of 7 strands each, No. 10 Birmingham wire gauge, or in specified cases of No. 8 or 7 wire gauge, making, when spun, a rope with a sectional area varying from 7/16 to 11/16.
(b). Solid copper rods ½ inch diameter [A. 0·20 in.].
Solid iron rods 1 inch diameter [A. 0·79 in.].
(c). Copper band or “tape” of sizes from ¾ × ⅛ to 2 or 3 × 3/16 inches [A. 0·09 to 0·38 or 0·56 in.].
(d). Copper tube ⅝ inch diameter outside, and ⅛ inch thick [A. 0·20 in.]
3. Although no definite rule exists for the proportional sizes of the conductor, it is usual and prudent in a large building to employ for the main conductors, which should come from the highest and most exposed points to the earth in the most direct way, a larger conductor than would be required for a small building, and the branches or connections to this main conductor may be smaller in sectional area than the principal one. Thus, a church tower with four angle pinnacles may be protected by four finials or points, one to each pinnacle, and these four parts fitted to rope of 7 wires No. 10 gauge [A. 0·10 in.], to be united to a continuous band round the parapet, from whence a rope of 7 wires No. 8 gauge [A. 0·15 in.] should descend into the earth; or an infirmary or workhouse built with wings would have, perhaps, three direct rod conductors, one to each chimney stack, and connections with the water spouts, or lead flashing made of small copper tape ¾ × ⅛ [A. 0·09 in.] soldered to the lead and worked round the rods.
4. The fewer joints the safer, and for this reason—the copper rope or tape is better than the rod or tube, as the former is made conveniently any required length, and the danger of a fault or break in the continuity is avoided. Of the necessary joints the rope requires one at its junction with the top rod or tube; this is made by brazing a small ring of brass (or copper) round the rope; the solid end thus formed being chased with a deep male thread, which fits the prepared base of the rod. The branch conductors or connections, with adjacent constructive or decorative iron work—as beams, girders; cresting, vanes, &c., are made by threading a bead with a similar ring to receive the branch, as that already described. Where the branch reaches its object a ring or solid coupling should be “tapped” into the girder or cresting, to ensure thorough metallic connection, if the destination of the branch be the lead flashing, the seven wires must be opened like a fan, and each wire strongly soldered with common plumbers’ solder to the lead—
(b). Copper or iron rods are made continuous by couplings of either metal, as the case may be, which should exceed the diameter of the rods by enough metal to allow of a good thread. These couplings should be hexagonal or octagonal in plan, to allow the workman a certain grip; and the thread should be of the kind called right and left, so that while screwing one length he may not unscrew the other. These conductors require very careful, steady workmen, as a great element of danger exists in these numerous joints.
5. The various natures of the buildings provided with conductors require separate, and often different treatment: but the principle in all cases is the same, viz., to attach the conductor closely to the fabric, and the more the conductor is made an integral part, as it were, the more efficacious it will be. Any attempts at so called isolation are opposed to the theory of protection by conductors. The mechanical means of fixing are best illustrated by diagrams, the chief objects to be considered are—
(e). Permanence or strength and durability.
(f). Room for expansion of the conductor.
(g). Facility in fixing without cutting or breaking the conductor.
(h). Neatness in appearance.
These objects are gained by a careful consideration of the materials to which the conductors are fixed by “holdfasts,” for stone, slate or tiles, wood, and iron. It is important that sharp bends be avoided. A string course, for instance, should be drilled, and the rod or rope passed straight through. Also, that any metal bodies in the line of the conductor should be connected with it by staples screwed into such bodies. It is most necessary that the ends of vane bolts or rods should be joined to the conductor, or, where this is impossible, should be fitted with an independent wire or rod to the earth.
6. The connection with the ground is of special importance, as the object of the conductor is to provide a free passage between the two currents, and if this be not done, a lateral discharge is pretty sure to result. A building provided with suitable conductors, properly fixed, should at all conditions of the atmosphere, allow a free course to the electricity, and be in all its parts electrically equivalent, and with this intention the several parts (as mentioned in answer to question 3) are brought into connection with each other or with the ground. The actual length of the ground conductor is fixed by the nature of the subsoil, as it is obvious that dry sandy soil is unsuitable for a termination. We therefore continue the rope or tape until a good damp earth is reached, if possible, a spring or open water—generally speaking, about 5 to 10 yards will be sufficient in most localities. The conductor is then buried 5 to 10 feet, or upwards, in the damp earth or water. If a rope, the several strands are unravelled and opened out: if a rod or tape, a discharging fork is usually attached to the end to promote the easy discharge, for which purpose it is also usual to fill the trench with charcoal. The trench must be dug with a slight fall from the building downward.
7. The extent of area supposed to be protected by the conductor is estimated by many as included in a radius of double the height of the conductor from the base line; but the immunity from accident enjoyed by many buildings situated at a greater distance from a number of tall factory chimneys; or to take an opposite example, in a city where there are many lofty spires or towers, would go to show that a number of conductors attached to tail objects, serve to obviate the dangers arising from lightning by providing, at many different points, a direct communication between the positive and negative currents which exist in the clouds and earth. We have never known a church spire, when the conductor was fixed in accordance with ordinary skill, injured by lightning; and the tall factory chimneys of our manufacturing towns afford strong corroborative evidence of the value of conductors, and this in two ways—first, because those to which conductors are fixed, do not get struck; and, second, because those unprovided with conductors, do get destroyed from time to time.
8. A reference to the answer to No. 3 question, will show that we consider that when several terminals are used, an increased diameter is advisable in the main or principal conductor; but it must be remembered that either of the conductors referred to in the answer to question 2, is greatly in excess of what many eminent electricians consider necessary. A single wire being thought sufficient of 3/32 inch diameter (A. 0·06 in.) for any ordinary current of electricity. But both the English and French Governments have thought it prudent to specify a copper body, with a sectional area of ½ inch in English, or 1 centimetre in French (0·40 in.)—partly to provide against corrosion, which would rapidly deteriorate a thin wire, and partly to obviate the danger of the melting of the smaller conductor under the continued force of an unusually strong shock of lightning. We, therefore, respectfully follow the decision of such experts as have, by careful experiment and considerable diligence, acquired the knowledge they possess—both as to the substance, the form, and the treatment of this subject; and have only to add the fact, that any small experience we have practically had, goes to support the conclusions already arrived at by these authorities.
FREEMAN & COLLIER.
24 & 26, Lever Street, Manchester.
1. Our upper terminals are made of copper or brass, plain spike or ball with spike at top, and three radiating from it, or four or five spikes radiating from the ball. Attached to the ball (screwed into it) is a solid rod of copper, to which the conductor is fastened, as explained below.
2. Conductor is made of good quality copper wire strand 7 ply: ⅜ inch [A. 0·11