HOLT Electricians Practice Exam

How many overload units are required for a 3-phase AC motor according to Section 430-36?

1. 1

2. 2

3. 3

4. 4

The correct answer is: 3

The requirement for overload units in a 3-phase AC motor, according to Section 430-36 of the National Electrical Code (NEC), states that one overload relay should be provided for each phase of the motor. This means that in a 3-phase system, three thermally responsive overload units are necessary to ensure that each phase is adequately protected. Each overload unit is designed to detect overload conditions and help prevent damage to the motor by interrupting the circuit if one phase of the motor experiences an overload. This configuration allows for even protection across all phases, as unbalanced loads could lead to overheating and failure if not properly monitored. Since each of the three phases requires its own overload protection to monitor their individual current levels, the total required would be three units total for a typical 3-phase motor application, confirming that the answer of three overload units is indeed the correct choice.