777 A' IMX'CTION MOTOR 



249 



squirrel-cage induction motors to the wood-working industry, the 

 motors serving as the headstocks of the lathes. 



As this type of motor develops very little starting torque, it 

 cannot be used where it must be started under any considerable 

 load. Another disadvantage is that its speed is not adjustable. 



106. Starting Squirrel-cage Motors. Small induction motors 

 up to 5 hp. can usually be connected directly across the line 

 without undue disturbance of the line voltage. Special starting 

 devices should be used for motors of 7.5 hp. and greater. 



Line 



FIG. 236. Switching ronm-rtions when motor is connected directly across line 



ure 236 shows the connections often used for the smaller- 

 si/ed motors where special starting devices are not required. 

 A doable-thlOW switch, when in the starting position, puts the 

 motor in series with three high-capacity fuses, one in each line. 



ise of the action of a spring, the switch can make contact 

 on this side only while it is held in position. When the switch is 

 thrown to the running position, the current is supplied through 



fuses designed to carry only the safe operating current of 

 the motor. This gives the motor over-load protection that 

 would not otherwise l>e obtained if fuBBfl suiliciently lai: 



rtinu: current were used during normal operation. 



in rods <>r other typ< ometimes in 



in the >!.-. rint to limit the starting current. Also, high- 



