A case in point occurred in May 1879. The steeple of the church at Laughton-en-le-Morthen was struck by lightning and damaged, the lightning conductor being thrown down and broken into two pieces. A correspondence on the subject ensued in the Times, and Mr. R. S. Newall had the remains of the conductor examined, with the following result:
‘The spire is 175 feet in height, and it had attached to it a thin tube, made of corrugated copper, about seven-eighths of an inch in external diameter and five-eighths internal. The copper is about one-thirty-second of an inch in thickness, and it weighs about one and a quarter pound per yard. It is made in short lengths, joined together by screws and coupling pieces, but there is no metallic contact whatever between the pieces, which are much corroded.
‘The conductor appeared to be fastened to the vane. It was not in contact with the building, which it ought to have been, but it was kept at a distance of about two-and-a-half inches from it by twenty-one insulators. The earth contact was obtained by bending the tube and burying it in the ground at a depth of from six inches to eighteen inches, the soil being dry loose rubbish; the length of the earth end was only three feet, with two short pieces of about a foot in length each tied to the tube by thin wires, thus forming altogether a most inefficient conductor. It was placed in a corner formed by a double stone buttress, which came between the conductor and a lead-covered roof attached to the spire, the distance between the conductor and the lead roof being about six feet six inches.
‘The lightning appears to have come down the conductor a certain distance, and, finding the road to earth bad, it passed through the buttress, dislodging about two cart-loads of stone, and then came down the cast-iron down pipes leading from the lead-covered roof and so to earth.’
Mr. Newall, in writing to the Times, goes on to say:—
‘Now if the conductor had been made of copper-wire rope, weighing about two pounds per yard, and fixed in contact with the spire, without insulators and with a proper earth contact, no damage whatever would have been sustained by the building; and if the conductor had been tested periodically by an expert he would have shown whether the conductor was good or useless. This examination ought to be insisted on, as the earth connection is often wilfully destroyed; but I have never in all my experience known a building which had a conductor properly fixed to suffer damage from lightning.’
What is really required is to make a lightning conductor of sufficient calibre to carry down the electric discharge, however great it may be, from the summit of the building into the earth, and that the earth contact should be above suspicion and thoroughly good in all seasons.
Fig. 26.
