rod to the building.
6. Ground end is coiled loosely in damp earth or a well.
RICHARD JOHNSON, CLAPHAM, & MORRIS.
180, Rottemore, Glasgow.
We beg to reply to your queries on the material, system, and fitting of lightning conductors, as practiced by us for over 25 years, during which time we have never had a building injured in which we have been engaged, and have fitted from 15,000 to 20,000 feet a year, without advertisement.
1. Uniformly solid copper, consisting of 1 centre concave point, about 14 inches long, presenting 8 sharp angles = 3½ inch surface; this is surrounded by 4 smaller points of same construction. These all terminate or spring out of a hollow copper ball, which is screwed on a copper tube ¾ inch diameter inside, and from 4 inches to 5 inches long, according to requirement. The copper cable is passed through this tube, is knotted inside of the ball, and the points are all screwed against it, which forms the point of contact, and thoroughly fixes the cable at the top; but the fixing of the top or terminal rod is fashioned in accordance with the requirements of the building or material to be fixed to.
2. Uniformly copper cable constructed of 49 strands, hard drawn square copper wire Nos. 17, 18, or 19 w.g.
3. We never use less than 6–inch surface, i.e., measuring the circumference of each wire, we contending that surface is the only power of the conductor. Up to 150 ft. we use No. 19 (= ½ inch diam.) [A. 0·20 in.],¾ inch for a longer length of cable (i.e., 17 or 18) [A. 0·44 in.].
4. Usually with a gun-metal screwed coupler.
5. With brass holdfasts, lined with porcelain, glass, or guttapercha.
6. Spread out end of strands of cable like a fan, and bury it in the moist earth a few feet deep, in an oblique way tending from building.
7. 30 to 40 yards.
8. We invariably run one cable from each terminal or top rod: but in spires we commonly take a connection from the bottom of the vane rod, and connect it to the main conductor, which goes to the highest point of vane or final: if the former, we fix a copper bush or disc to the vane rod at foot of vane, which is fast to cable, and a corresponding one on vane, with cable at highest point, when the cable is fringed out, presenting its 49 points, and by these discs the vane revolves with that portion of the conductor attached, and the point of contact is given by the discs.
C. H. PENNYCOOK & CO.
All Saints’ Works, Derby.
1. Form for upper terminals:—A straight copper tube,¾ inch diameter; thickness of metal, 15 B.W.G. [A. 0·15 in.], with solid copper point (no branches); the point is soldered and rivetted into the tube; or a solid copper rod,½ inch diameter [A. 0·20 in.], tapering towards the top.
2. Material and dimensions of conductor:—Either a copper band of 2½ inches wide and No. 16 B.W.G. thickness [A. 0·16 in.]; or a copper wire rope,½ inch diameter, of 6 strands, each strand containing 6 wires [A. 0·20 in.].
3. Proportion between length and sectional area of conductor:—The ½ inch copper rope [A. 0·20 in.], or 2½ × 16 B.W.G. band [A. 0·16 in.], is used for heights not over 120 feet; for higher buildings, a ¾ inch rope [A. 0·44 in.] or band, 2½ × 12 B.W.G. [A. 0·27 in.] should be used.
4. Joint, how made:—Joint is made between band and copper rod with a brass screwed socket, the rod is soldered and rivetted into socket, and the band is soldered round socket, then soldered and rivetted. When the copper rope is used, a hole is drilled into socket, same diameter as rope, at the lower end, and turned out conical shape; the rope is then passed through the socket, the ends spread out, and the spaces filled up with solder.
5. Attachment to building:—The conductor is fixed close to building without insulators, and is brought into close contact with the spouting; is closely attached to chimney and walls by means of copper straps and copper nails driven into the masonry.
6. Ground connection:—Should a good, permanent drain be near, the conductor is brought to it and bound round and firmly fixed.
If there should be an open drain or brook, the conductor is brought under it at sufficient depth that if the stream be dry at any time there will be sufficient moisture to carry away the charge without disruption. Should there be neither drain pipes nor brook sufficiently near, the conductor is taken from 12 to 20 feet below the surface to the clay, where it is certain to be always damp, even in seasons of the greatest drought ever known.
In no case should the earth connection be taken into a closed tank or well.
If a band be used, it should be cut into strips about 18 inches long and laid in different directions; rope should be unwrapped and spread in a similar manner.
7. Supposed area protected:—It is impossible to determine exactly the area the conductor protects. It is erroneously supposed that the rod will protect buildings within its radius, but experience will not bear out this axiom. Many instances may be related of buildings being struck much within the radius of well-protected churches or chimneys.
The protection a conductor affords depends to a great extent on the relative positions of the electric discharge and the objects that it may meet in its course. As a general rule, a church with a high spire with a proper conductor may be considered to protect the remainder of the edifice; but a low, straggling building should have several conductors at the outside highest points.
8. If there is more than one terminal is the size of conductor increased?—No; as sufficient material should always be used to carry off without disruption the heaviest known charge, it is unnecessary to increase the size of conductor. Should two or more upper terminals be connected with the main conductor, the size of material need not be increased; for if two or more terminals receive the charge simultaneously it necessarily follows that it is sub-divided; therefore the conductor will have no more work than if one point only had been struck.
Note.—We quite agree with Snow Harris regarding insulators, that if there be anything in insulators they are a disadvantage, for if the building be struck in any other part than the conductor, the current cannot easily find its way to the conductor. The current will take the line of least resistance; therefore it is reasonable to assume that the building is more certain to escape the disruptive force of lighting when the conductor is in close proximity with the building.
JOHN DAVIS & SON.
Bigg Market, Newcastle-on-Tyne.
1. For upper terminals I generally use ½ inch diameter solid copper rod [A. 0·20 in.], or ¾ inch diameter tube [A. 0·24] with four points, and I fix them 4 or 6 feet above the building they are intended to protect. I always endeavour to get the upper terminal as near the size of the conductor as is consistent with strength. I make my points of the best copper tipped with platinum.
2. For the conductor I use ½ inch diameter copper wire rope [A. 0·20 in.], which is (in my opinion) the best and most applicable conductor used, as it appears to be an open question, at present, whether it is surface or mass which conducts. If it is mass, then a tube conductor is insufficient. If it is surface, then a solid rod is superfluous. The copper tape conductor I consider the worst form of any, as it bends too easily round sharp corners, projections, &c., of buildings, which is a thing to be avoided as much as possible. A conductor should be brought to earth as direct as possible, and with no bends if they can be avoided. The copper wire rope conductor has both surface and mass
