ELECTRICAL MACHINERY 495 



To find amperes to be conducted. 



C = Y = ^ =0.5 per lamp. 



0.5 X So = 25 amperes for all lamps. 

 112110 = 2 volts drop on line. 



C.M. = K XLX C = '-79X(iQX2)X2 5 = 26 , 975 . 



C M. = circular mil area. 

 K = 10.79. 

 L = 100 X 2 = 200 feet. 



C = 2 5 . 



By comparison with the wire table (670) the next larger size than 

 26,975 is B. & S. No. 5. 



Wiring calculations for a motor. To find the size of wire to 

 transmit any given horse power any distance when the voltage and 

 efficiency are known. 



C M - H P X 746 X L X IQ.79 



E X e X $M 



E = voltage required by motor. 

 e = drop on line. 

 H. P. = horse power of motor. 

 % M = efficiency of motor in decimals. 



Example. What size of wire is required to conduct current to a 

 220-volt 6 H.P. motor located 175 feet from the dynamo? The 

 drop on the line is to be 6 volts and the efficiency of the motor 80 

 per cent: 



r M _H.P. X746XLX iQ-79 



EXeX^M 

 _6 X 746 X 175 X 2 X 10.79 



220 X 6 X .80 

 = 15,984 C. M. 

 = No. 8 B. & S. 



To find the current required by a motor when the horse power, 

 efficiency and voltage are known. 



H. P. X 746 



EX#M 



Example. What current is furnished to the motor in the previous 

 problem ? 



c _ H. P. X 746 



EX#M ' 



_ 6X 746 



220 X 80 



= 25.4 amperes. 



