SWITCHBOARDS AND SWITCHBOARD APPLIANCES. 345 



voltage, the A.C. solenoid is compounded, that is, it is provided 

 with two windings, one of which is connected to a potential trans- 

 former and the other is connected to a current transformer. 



In practice, condensers are connected across the contacts C and 

 TT' to reduce the amount of sparking, and reversing switches 

 are arranged to reverse the currents through C and through TT' 

 (once a day) so as to give equal wear on the contact points. 



