A 3 phase, 6 pole induction motor operates on 440 V, 50 Hz, supply. If the actual speed of the motor is 960 rpm the slip will be

• A. 5 %
• B. 0.4 %
• C. 6 %
• D. 4 %

Answer: (D)

Ns = 120f/P
Slip=(Ns-Nr)/Ns
Ns = 1000 and Nr = 960
from equation of slip, S = (1000-960)/1000
S = 0.04 or 4%