The ‘crawling’ in an induction motor is caused by

The correct answer is: B. low voltage supply.

Crawling is a phenomenon that occurs in induction motors when the voltage supply is low. When the voltage supply is low, the motor’s magnetic field is weakened, which causes the motor to run at a slower speed. This can cause the motor to make a whining or growling noise, and it can also cause the motor to overheat.

The other options are incorrect because:

• High loads do not cause crawling. In fact, high loads can actually cause the motor to run faster.
• Improper design of the machine can cause a variety of problems, but it is not likely to cause crawling.
• Harmonics developed in the motor can cause a variety of problems, but they are not likely to cause crawling.

In conclusion, the correct answer is: B. low voltage supply.