Master Electrician Practice Exam

What is the maximum full-load current rating for each motor to be installed without individual overcurrent protection if rated less than 1 hp on a 120-volt, 20-ampere branch circuit?

1. 4 amperes

2. 5 amperes

3. 6 amperes

4. 7 amperes

The correct answer is: 6 amperes

The maximum full-load current rating for motors rated less than 1 horsepower (hp) on a 120-volt, 20-ampere branch circuit is determined by the National Electrical Code (NEC). According to NEC guidelines, motors that are rated less than 1 hp can be installed without individual overcurrent protection, provided they do not exceed certain current limits. For a 120-volt circuit, the permissible full-load current for a motor under these conditions is 6 amperes. This limit ensures that the motor operates effectively without the risk of tripping the circuit breaker or causing overheating, while still providing adequate protection to the circuit. By keeping the maximum current rating at 6 amperes, systems are designed to maintain safety and reliability, allowing for the use of smaller motors without additional protections. Motors rated above this current would necessitate individual overcurrent protection to manage potential overload scenarios. Hence, the selection of 6 amperes as the maximum full-load current is based on established standards aimed at safeguarding both the motor and the circuit.