44Q ENGINEERING ON THE FARM 



be a maximum quantity of moisture and where the ground 

 becomes moist early in the storm. Steel windmill towers 

 should be grounded by wires fastened to the lower part 

 of the tower and buried in the moist earth. 



Because of varying soil conditions, no specific depth can 

 be given. There is no danger from excessive depth, and 

 many lightning-rod systems have been failures because of 

 shallow grounding. Eight or ten feet is an advisable depth 

 under nearly all conditions. One hundred to two hundred 

 pounds of scrap iron buried in a large hole around the 

 ground conductor is desirable. Occasionally where digging 

 is hard a trench is dug and filled with scrap iron placed 

 around and in close contact with the ground conductor. 

 Some authorities recommend extending the ground conductor 

 into a well. 



Detailed instructions relating to wiring a building for 

 protection from lightning are covered by Alfred J. Henry 

 in Farmers' Bulletin 367, U. S. Department of Agriculture. 



SUMMARY 



No better conclusion can be drawn for this chapter than 

 that given by Professor S. C. Lee of the Manitoba Agricul- 

 tural College, in Extension Bulletin No. I, after an elaborate 

 series of experiments to determine the efficiency of lightning 

 rods 



Copper and galvanized iron are the standard materials 

 used for lightning conductors. Conductors of sufficient 

 size to carry the heavy lightning currents should weigh at 

 least 3 ounces per foot when made of copper and 5 ounces 

 per fopt when made of galvanized iron. 



Any shape of cable that is desirable and easily put up may 

 be used. Cable made of twisted strands of either iron or 

 copper is very suitable. 



All parts of the wiring should be connected into one sys- 

 tem and no blunt ends or stubs left ungrounded. Where 

 joints must be made, they should be very secure, and 



