Fig. 1,043.—Horn type lightning arrester. In this type of arrester, two wires, after approaching within a short distance of one another, are bent divergently. These wires are supported on insulators. One of them is connected to the line to be protected and the other is earthed. The normal line pressure is insufficient to bridge the gap, even at its narrowest portion, but an extra high pressure whether due to lightning or to other disturbing phenomena, will bridge the gap at its narrowest point and establish a path to earth. When, however, the main current attempts to flow across, phenomena of electromagnetic repulsion force the arc upward along the horns, lengthening and attenuating it, until it finally becomes extinguished.
Ques. How should lightning arresters be grounded?
Ans. They should be connected to ground with No. 6 B. & S. gauge copper wire or larger. Gas pipes within a building must not be used for a ground connection.
Fig. 1,044.—Ground connection for lightning arrester.
Fig. 1,045.—Carbon lightning arrester with fuses as used on telephone lines. The arrester consists of two blocks of carbon separated a small distance by a thin sheet of insulating mica, which is perforated with one or more holes; a high voltage charge on the line will jump through the hole in the mica from the carbon on the line side to the lower carbon, which is connected with the ground; the fuses protect the instruments against foreign currents which might damage, although not of sufficiently high pressure to jump to earth; sometimes the connections are reversed so that the fuse is between the line and the earth.