Chapter 2, Problem 1SQ

If the contacts on a manual starter cannot be closed immediately after a motor overload has tripped them open, what is the probable reason?

To determine

Explain the probable reason for allowing the time duration to reset the starter contacts after they tripped off by the overload protection equipment of the motor.

Explanation of Solution

Discussion:

The overload protection of the motor trips off (open) the contacts of a motor starter when the load exceeds the normal range. The overload protection equipment (heater) gets heated during the overload condition.

The contacts of the starter can reset only after the overload protection equipment cools completely. If the contacts are closed immediately, the heater does not cool properly due to the insufficient time and it lead to damage the motor as the overload still exists.

Conclusion:

Thus, the contacts of the motor starter cannot close immediately when the motor overload has tripped them open.