An induction motor draws a relatively high current when it is started; typically five to six times the full-load Amperes of the motor. This "in-rush" of current energizes the motor windings creating the fields that provide the torque. This in-rush can be modified by the motor manufacturer but that, in turn, also changes the ability of the motor to start under load. The usual practice is to design the windings to tolerate these large currents for a short period of time during the motor's acceleration to full speed, at which time the current will have dropped to a value that the motor can tolerate indefinitely.
Conditions permitting, an induction motor is usually started "across-the-line" at full voltage, by closing a set of contacts that connect the motor terminals directly to the electrical supply.
This graph shows the torque and current characteristics as functions of the speed for a 15-HP, 230-V, 60-Hertz, 1,750-rpm, Code-G squirrel-cage induction motor. The full-load current for this motor is 42 Amperes but the starting ("locked-rotor") current is 228 Amperes when started across-the-line. The full-load torque is about 45 pound-feet but the starting torque is 1.58 times as large. 
Notice that the torque continues to increase from the starting value as the motor accelerates until a speed of about 1,500 rpm is reached, after which the torque drops sharply toward zero at the synchronous speed of 1,800 rpm. The rated torque occurs at a speed about 3 percent less than 1,800 rpm.
Notice also that the current also remains at a high value until a speed near rated (1,750 rpm in this case) is reached. In fact, the current is at least twice rated value until the speed comes within about 125 rpm of rated speed.
These large currents during motor startup and acceleration cause rapid heating of the motor conductors. The actual temperature rise depends upon the time it takes to reach operating speed, which depends upon the inertia of the motor and the driven load, as well as any power output required from the load. This is why the motor manufacturer may also specify the maximum inertia the motor can safely accelerate. There may also be a limit on the number of starts permitted within a specified period of time.
If the motor should fail to start for any reason, it would continue to draw these heavy starting currents until it was either destroyed or the circuit opened due to fuse or circuit breaker operation. Ordinarily, the motor overload relay would interrupt power to the motor, but back-up protection is usually provided in the electrical system by fuses or a circuit breaker.
