has a radius equal to the height of the conductor; but one firm considers that this should be multiplied by five or six times; while another asserts, “that no appreciable extent is protected by a single rod conductor;” and another, that “many instances may be related of buildings being struck much within the radius of well protected churches or chimneys.”
We have no experience at present to enable us to form a definite opinion on this point. The Committee of the French Academy, gave the radius as equal to twice the height of the conductor from the ground, but buildings have undoubtedly been injured within this limit. The writer does not think that a greater radius than the height should be taken: but thinks that this is one of the most important questions that the Conference could determine. Calculation might, to a certain extent, settle the point: but it is more a case for experience.
8. If there is more than one terminal, is the size of the conductor increased?
This question has been partially considered. (See No. 3.)
Some firms do not consider any increase necessary: others think that when two or more terminals are used, the main rope should be somewhat enlarged; while others run one cable from each terminal, or make the conductor of sufficient capacity to carry off the double charge.
The writer considers that every conductor should be complete in itself: or, if this is inconvenient, then the size of the main conductor should be enlarged in proportion. It does not at all follow, as one firm implies, that if two or more terminals receive the charge simultaneously, it is necessarily sub-divided. Each charge may be full and complete in itself, and be sufficient to fill the wire; and, therefore, if the main conductor be not increased, accident may result.
There is no doubt whatever that great consideration should always be given to the lessons of experience, and the opinions of those who have made the erection of lightning conductors for 35 years their especial practical study, are much entitled to weight; but such practice may have originally been based on error, and the teachings may not have been guided by science. Where such variety of practice abounds, there must be fallacy somewhere, and, therefore, danger; and not the least of the beneficial labours of the Conference will be to point out to these different practical men, where their faults and their departures from truth exist.
W. H. PREECE.
August 8th, 1879.
APPENDIX C.
REPLY FROM MANUFACTURERS, RECEIVED AFTER THE COMPLETION OF THE ANALYSIS WHICH FORMS APPENDIX B.
Faraday Steam Works,
St. John’s Road, Huddersfield.
11th November, 1879.
Sir,
Enclosed we have pleasure in handing you our replies to the eight questions which you ask lightning rod manufacturers and erectors, together with three tracings, showing our system of protection under different conditions. In the case of Nottingham Castle we considered it necessary, on account of the rock on which the castle was built, to adopt an extensive system of lateral points in earth termination, by running all the main conductors from the building down the shrubbery into the moat, where we formed the flat copper band into the form of gridirons, in which several hundred feet of the copper band has been used, and the termini of the ribs pointed, and the whole being sunk eight feet, and two cart-loads of gas carbon laid over each grid.
Yours obediently,
SANDERSON & CO.
REPLIES TO THE QUESTIONS OF THE LIGHTNING-ROD CONFERENCE.
I.—Usually a length of copper tube 5 feet long 1 inch diameter × No. 8 B.W.G., which is termed the elevation rod, surmounted by a solid copper point, forged from ⅞th of an inch round bar, wrought three parts of its length to a square tapering point, the said elevation rod and point are screwed together by a copper ball-shaped union, into which are screwed four smaller points at an angle of 45 degrees. When fixing lightning conductors on church spires and turrets we usually run the copper tape a few inches above the vane or finial, having previously prepared and pointed the tape; by this system all joints are avoided.
II.—We, the sole inventors, manufacture the solid copper tape lightning conductors of the following sizes:—
| Nos. | 1 | 2 | 3 | 4 | 5 | 21 | 22 | 23 |
|---|---|---|---|---|---|---|---|---|
| in. | in. | in. | in. | in. | in. | in. | in. | |
| ⅝×1/12 | ¾×⅛ | 1×⅛ | 1½×⅛ | 2×⅛ | 1×1/16 | 1½×1/16 | 2×1/16 | |
| [A | ·05 | ·09 | ·13 | ·19 | ·25 | ·06 | ·09 | ·13] |
and in continuous lengths up to 500 and 600 feet.
III.—Yes. For heights of say 50 feet we recommend our No. 2 (¾ in. × ⅛ in.) size; for 100 feet our No. 3 (1 in. × ⅛ in.) size; and for 200 feet or over, our No. 4 (1½ in. × ⅛ in.) size; or our Nos. 21 (1 in. × 1/16 in.), 22 (1½ in. × 1/16 in.), or 23 (2 in. × 1/16 in.) according to position and circumstances.
IV.—In the case of church spire or turret conductors we have no joints whatever, as described in Answer I., but where elevation rods and points are used we make a copper coupling, screwed at one end to receive the elevation rod, and at the other end to receive the copper tape, which is firmly rivetted into the coupling, and thence soldered or brazed. But when a complete system is employed with branches or tributaries, running from several points on to the main conductors, we make the joint by means of copper rivets, and then solder.
V.—By means of gun metal clips, or holdfasts, let into the building, which secures the copper tape in close contact with the face of the building. Under no circumstances do we use glass, ebonite, or other insulators.
VI.—In good moist earth 5 feet or 6 feet deep we simply run the copper tape out from the building some 20 feet, and
