SWITCHING EQUIPMENT 



579 



the magnetic repulsion suddenly set up by a large rush of current 

 consequent upon a heavy overload or short>circuit. This with 

 very few, if any exceptions, results in damage to the switch, 

 caused by its opening under heavy load. To obviate such possible 

 results, disconnecting switches should be provided with safety 

 locks which hold the switch blade in a closed position until opened 

 by the operator. The catch is closed automatically when the 



FIG. 371. Showing Method of Bringing Low-tension Leads from Outdoor 

 Transformers to Building through a Tunnel. 



switch is closed, and it may be of a design so as to serve in addition 

 as a guide for the blade in closing. 



The ordinary high-voltage knife-blade disconnecting switch, 

 operated by a hook on the end of a long rod, necessitates an amount 

 of space of the operator directly below the switch and perpendicu- 

 lar to its base, depending both upon the length of the blade and of 

 the rod used to open and close it. 



Where the space is restricted this design may therefore not 

 be the best suitable and a switch as shown in Fig. 373 has been 

 developed for such conditions. It is operated from directly below 



