Fig. 1,041.—Mason multi-discharge lightning arrester. The construction of this arrester is based on the well known principle that lightning discharges more readily at points or angles than elsewhere. The wire is wound around square carbon rods, which are connected to the ground, the line being insulated from the rods by sheets of mica. The wire itself being square, instead of round, adds to the efficiency of the arrester, by increasing the number of points or angles.
Ques. For what kind of service is the form of arrester just described used?
Ans. It is suitable for telegraph and telephone lines where currents of very low voltage are employed.
Ques. Why is it not used on lines employing higher voltage, such as in electric light and power stations?
Ans. Current at high pressure would follow the lightning across the gap and establish an arc or continuous flame from one plate to the other thus quickly destroying the plates and causing other more serious damage.
Ques. What provision is made to prevent the destruction of arresters by the line current?
Ans. Lightning arresters used on heavy duty circuits are designed to rupture the arc as soon as formed.