612 ELECTRICAL EQUIPMENT 



The wiring connections of lightning arresters are important. 

 The discharge circuit should contain minimum impedance and 

 hence must furnish the shortest and most direct path from line 

 to ground. The most severe disturbances which an arrester is 

 called upon to handle are of high frequencies, and it is therefore 

 imperative to eliminate all necessary inductance. The features 

 favorable for low inductance are short length of conductor, large 

 radius bends and large surface of conductor. Copper tubing is 

 strongly recommended for wiring high-voltage arresters. It has 

 the advantage over either copper strip or solid conductors in that 

 it is easily supported, requires fewer insulators, and is therefore 

 cheaper to install. 



In all lightning arrester installations, good, permanent, low- 

 resistance grounds are essential for the satisfactory operation of 

 the arresters. Poor grounds cause loss in protection with an 

 ultimate loss in apparatus. It has been customary to ground a 

 lightning arrester by means of a large metal plate buried in a bed 

 of charcoal at a depth of 6 or 8 feet in the earth. A more satis- 

 factory method of making a ground is to drive a number of 1-inch 

 iron pipes 6 or 8 feet into the earth about the station, connecting 

 all these pipes together by means of a copper wire, or, preferably, 

 by a thin copper strip. A quantity of salt should be placed 

 around each pipe under the surface of the earth and the ground 

 thoroughly moistened with water. It is advisable to connect 

 these earth pipes to the iron framework of the station, and also 

 to any water mains, metal flumes, or trolley rails that are avail- 

 able. For the usual size station the following recommendation is 

 made: place three earth pipes equally spaced near each outside 

 wall, making twelve altogether, and place three extra pipes 

 spaced about 6 feet apart at a point nearest the arrester. 



Where plates are placed in streams of running water, they 

 should be buried in the mud along the bank in preference to laying 

 them in the stream. Streams with rocky bottoms are to be 

 avoided. Whenever plates are placed at any distance from the 

 arrester it is necessary also to drive a pipe in the earth directly 

 beneath the arrester, thus making the ground connections as short 

 as possible. Earth plates at a distance cannot be depended upon. 

 Long ground wires in a station can not be depended upon unless a 

 lead is carried to the multiple earth pipes described above. As it 

 is advisable to occasionally examine the underground connections 



