32 



hold the moisture." There is doubtless some virtue in this, though the ground-plate 

 and other methods are better. 



On an L- or T-shaped building there should be at least three groundings. Two 

 of the damages suffered by the Protected Mutual happened in the following man- 

 ner : Both buildings were T-shaped. There was a ground-rod at each end of 

 the main part, and from the main system a cable ran along the ridge of the other 

 wing and a point was placed about five feet from the end, but the cable was not 

 continued further, there was no ground-rod for this part of the system. Later a 

 telephone line was run into the house, entering near this stub end. The lightning 

 flash struck the point on this wing, and divided, part following the cable and 

 part jumping to the telephone line. If there had been another ground-connection 

 for this portion of the system probably no damage would have occurred. 



All ground-rods should go deep enough to be in perpetual moisture. In Michi- 

 gan where rods are subject to insurance inspection it is insisted that ground-rods 

 must go at least eight feet in the earth, and many are sunk ten feet. 



Impoetance of Proper Grounding, 



Here let a note of warning be sounded to everyone who is having his buildings 

 rodded : Be present and see the ground-rods put down. Know for yourself that 

 the rods are actually down eight feet or more. Do not take anybody's say-so on 

 this point. Lightning-rod men, as a class, are as honest as' any other class of the 

 community, but an odd one is unscrupulous and will " scamp " the job if possible. 

 We have a record of a case where the rodding agent instead of putting the cable 

 eight feet straight down in the earth coiled it up and buried it in a small hole in 

 dry earth, and the barn was burned by lightning the very day it was rodded. Noth- 

 ing could be more dangerous. When electric power companies want to prevent the 

 lightning charge from coming in on the line wires and damaging their machinery 

 they make a " choke "-coil of several turns of the wire just inside the station and 

 beside the line put a ground-wire separated from the line by a short air-gap. When 

 the lightning charge follows the line to the station the " choke "-coil makes it so 

 difficult for the sudden current to pass that it jumps the air-gap to the ground-wire 

 in preference and thus escapes to the earth. Now the coil at the foot of the light- 

 ning rod acts just in the same way. It chokes the current back and makes it take 

 some other path, down through the building, probably firing the building on the way. 

 In a coil self-induction is very high, hence the choking effect. 



Consequently, let us say again, look well to the groundings. They are prob- 

 ably the most vital part of the system. See the ground-rods put in. 



3. Systems. — The cable beginning at one ground-rod should extend up the 

 corner, make a gradual turn at the eaves, go up the edge of the roof to the peak, 

 along the peak to the other end, down the edge of the roof to the eave, and down 

 the corner to the other ground. All turns should be rounded rather than angular. 



All the cables on a building should be connected in one system. Sometimes it 

 is found that on an L-, T- or U-shapcd building, for instance, the rods on the 

 one part are not connected with those on the other. Numerous instances are 

 reported where damage has occurred between these two systems, the lightning 

 striking the one system and part of the current jumping across to the other. Con- 

 sequently, divided systems should be scrupulously avoided. When a cupola is 

 encountered the cable should go around rather than over it, the point on the cupola 

 being connected to the cable below. ^ [ 



