Lightning Page 143

Every ground terminal within the housing, as well as a connection to the housing itself, is brought to one common ground point called the "prime ground terminal" which is connected to earth ground through the lowest resistance path possible. Railway signalmen have told of standing inside a wayside housing during a storm and seeing the arresters constantly flashing like a small fireworks display. A severe surge will cause a railroad arrester to blow off its glass covering with a report like a gunshot.

Although telephone lines often run long distances above ground, many types of cable are shielded, and surges occur mainly in the shield where they harmlessly bleed off to ground.

In the home, the telephone line is connected to ground through two carbon fuses of carefully calculated resistance. One carbon fuse connects each side of the line to ground, thereby holding each side of the line at an equal potential above ground, thus zero volts with respect to one another so far as alien power surges are concerned.

At the exchange each incoming conductor is connected to ground through a carbon fuse and all the ground connections made through one common terminal.

Commercial broadcasting stations, as a general rule, use relatively crude lightning protection methods. A piece of heavy bar