EFECTS OF LIGHTNING

Radio Record, Volume I, Issue 9, 16 September 1927, Page 14

EFECTS OF LIGHTNING

FIRE UNDERWRITERS’ REGULATIONS, A Kelburn reader wishes to know the possible and probable effects fo lightning upon a set or user without an arrester in the aerial circuit. If the set was in use when lightning struck the aerial, the chances are that there would not be much left of the wiring of the set, as the track of the discharge would be through the aerial circuit to earth. This would offer an indirect path for the lightning to get to earth, and would. also offer resistance. When lightning | meets with ny opposition to its progress the tendency is to branch off in all directions, seeking an easier path, and this tendency would probably lead it through the whole of the set wiring, which would at least receive considerable damage. A listener with headphones might get a severe shock direct from the ‘phones, but it any case a person situated anywhere in a house without a wireless installation sometimes gets what is known as a "return shock" when the lightning discharge is close at hand. When a highly elec-

trified cloud passes overhead it attracts to the nearest point of all conductors. below it a charge of the opposite elec- | tricity to its own, so that a person s‘anding about has a strong charge of elec: | tricity attracted from the earth to his head. When the discharge of the cloud: takes place to a lightning conductor, : chimney, or other high object near at. hand, the charge in the person’s head suddenly returns to earth, giving the "return shock," which may be slight or fairly severe, but not fatal. | Not very much is usualy known about lightning, and on that account there is a tendency to overrate the danger from it. © When we take into account the

large number of aerials in use and the rare occasions upon which one is struck, the danger is shown to be fairly slight. But when an arrester is properly fixed on the outside of the building a lightning discharge will jump the arrester and find its way direct to earth, and, provided that the discharge is not abnormally large, there is a good chance that the set would be unharmed. The function of an arrester is only to provide an easier path to earth than through the set when the latter is in use. When the set is not in use the putting over of the switch to earth the acrial should never be neglected, as by that means the set is protected, and the aerial, acting as a lightning conductor, affords an actual protection against the house itself being struck. When the aerial is so earthed the lightning arrester is out of action for the time bei..g. The earthing switch should also be placed outside the house in a convenient position by the window. The foregoing remarks show that in neglecting to instal a lightning arrester a certain amount of risk, though small, i being run, but there is another aspect of the case. The fire underwriters’ regulations require that no less gauge than fourteens wire shall be used for the lead-in and earth connection, that an earthing switch shall be provided, and that a lightning arrester of good pattern be installed, and it is very much to listeners’ own interests that they should comply with these three important regulations, as it is only in case of such compliance that the company insuring the property waives any right to make an increase in the premium on account of extra risk. When a thunderstorm is close at hand it is wise to discontinue listening, earth the aerial, and disconnect both aerial and earth wires from the terminals of the set as a simple precaution, but there should be no nervous apprehension about it.