Since 1971 edition NEC, 3-phase motors only need two phases protected with properly sized overload protection.

Since 1971 edition NEC, 3-phase motors only need two phases protected with properly sized overload protection.

• A. True
• B. False
• C. Three
• D. None

Answer: (B)

Overload protection for three-phase motors must cover all ungrounded conductors that supply the motor. The reason is that if a motor loses a phase or runs with an imbalance, the remaining windings can overheat quickly, and protection on only two of the three lines won’t reliably prevent damage. The NEC requires overload protection in each ungrounded conductor, or a single device that simultaneously interrupts all three phases. So the statement is false: you don’t limit protection to two phases.

Overload protection for three-phase motors must cover all ungrounded conductors that supply the motor. The reason is that if a motor loses a phase or runs with an imbalance, the remaining windings can overheat quickly, and protection on only two of the three lines won’t reliably prevent damage. The NEC requires overload protection in each ungrounded conductor, or a single device that simultaneously interrupts all three phases. So the statement is false: you don’t limit protection to two phases.