Chapter VI: Section III: Code of Rules for the Erection of Lightning Conductors

The following Code of Rules should be carefully attended to in drawing out a specification for a Lightning Conductor, the reasons for each being given in the previous Sections and in the Appendix:—

=Points.=—The point of the upper terminal should not be sharp, not
sharper than a cone of which the height is equal to the radius of
its base. But a foot lower down a copper ring should be screwed
and soldered on to the upper terminal, in which ring should be
fixed three or four sharp copper points, each about 6 in. long. It
is desirable that these points be so platinized, gilded, or nickel
plated as to resist oxidation.

=Upper Terminals.=—The number of conductors or points to be specified
will depend upon the size of the building, the material of which
it is constructed, and the comparative height of the several
parts. No general rule can be given for this; but the architect
must be guided by the directions given at pp. 12 to 14. He must,
however, bear in mind that even ordinary chimney stacks, when
exposed, should be protected by short terminals connected to the
nearest rod, inasmuch as accidents often occur owing to the good
conducting power of the heated air and soot in a chimney (p. 2).

=Insulators.=—The rod is not to be kept from the building by glass or
other insulators, but attached to it by metal fastenings. (See p.
11.)

=Fixing.=—Rods should preferentially be taken down the side of the
building which is most exposed to rain. They should be held
firmly, but the holdfasts should not be driven in so tightly as to
pinch the rod, or prevent the contraction and expansion produced
by changes of temperature.

=Factory Chimneys.=—These should have a copper band round the top, and
stout, sharp, copper points, each about 1 ft. long, at intervals
of two or three feet throughout the circumference, and the rod
should be connected with all bands and metallic masses in or near
the chimney. (See p. 5.) Oxidation of the points must be carefully
guarded against.

=Ornamental Ironwork.=—All vanes, finials, ridge ironwork, &c., should
be connected with the conductor, and it is not absolutely
necessary to use any other point than that afforded by such
ornamental ironwork, provided the connection be perfect and the
mass of ironwork considerable. As, however, there is risk of
derangement through repairs, it is safer to have an independent
upper terminal. (See p. 4.)

=Material for Rod.=—Copper, weighing not less than 6 oz. per foot run,
and the conductivity of which is not less than 90 per cent. of
that of pure copper, either in the form of tape or rope of stout
wires—no individual wire being less than No. 12 B. W. G. Iron may
be used, but should not weigh less than 2¼ lbs. per foot run. (See
pp. 5 to 10.)

=Joints.=—Although electricity of high tension will jump across bad
joints, they diminish the efficacy of the conductor; therefore
every joint, besides being well cleaned, screwed, scarfed, or
rivetted, should be thoroughly soldered. (See p. 10.)

=Protection.=—Copper rods to the height of 10 feet above the ground
should be protected from injury and theft, by being enclosed in an
iron pipe reaching some distance into the ground.

=Painting.=—Iron rods, whether galvanized or not, should be painted;
copper ones may be painted or not according to architectural
requirements.

=Curvature.=—The rod should not be bent abruptly round sharp corners.
In no case should the length of the rod between two points be more
than half as long again as the straight line joining them. Where a
string course or other projecting stone work will admit of it, the
rod may be carried straight through, instead of round the
projection. In such a case the hole should be large enough to
allow the conductor to pass freely, and allow for expansion, &c.

=Extensive Masses of Metal.=—As far as practicable it is desirable
that the conductor be connected to extensive masses of metal, such
as hot-water pipes, &c., both internal and external; but it should
be kept away from all soft metal pipes, and from internal
gas-pipes of every kind, respecting which see page 15. Church
Bells inside well protected spires need not be connected.

=Earth Connection.=—It is essential that the lower extremity of the
conductor be buried in permanently damp soil; hence proximity to
rain-water pipes, and to drains, is desirable. It is a very good
plan to make the conductor bifurcate close below the surface of
the ground, and adopt two of the following methods for securing
the escape of the lightning into the earth. A strip of copper tape
may be led from the bottom of the rod to the nearest gas or water
_main_—not merely to a lead pipe—and be soldered to it; or a tape
may be soldered to a sheet of copper 3 ft. × 3 ft. and 1/16 in.
thick, buried in permanently wet earth, and surrounded by cinders
or coke; or many yards of the tape may be laid in a trench filled
with coke, taking care that the surfaces of copper are, as in the
previous cases, not less than 18 square feet. Where iron is used
for the rod, a galvanized iron plate of similar dimensions should
be employed.

=Inspection.=—Before giving his final certificate, the architect
should have the conductor satisfactorily examined and tested by a
qualified person, as injury to it often occurs up to the latest
period of the works from accidental causes, and often from the
carelessness of workmen. (See p. 14.)

=Collieries.=—Undoubted evidence exists of the explosion of firedamp
in collieries through sparks from atmospheric electricity being
led into the mine by the wire ropes of the shaft and the iron
rails of the galleries. Hence the headgear of all shafts should be
protected by proper lightning conductors.

(Signed)

W. GRYLLS ADAMS.
W. E. AYRTON.
LATIMER CLARK.
E. E. DYMOND.
G. CAREY FOSTER.
D. E. HUGHES.
T. HAYTER LEWIS.
W. H. PREECE.
G. J. SYMONS.
JOHN WHICHCORD.

_December 14th, 1881._