CEI CEI Motor & Motor Control Inspection 1 — Questions and Answers
Question 1: According to NEC Article 430, what is the minimum branch-circuit conductor ampacity for a single motor?
- 100% of the motor full-load current
- 125% of the motor full-load current (Correct answer)
- 150% of the motor full-load current
- 80% of the motor full-load current
Correct answer: 125% of the motor full-load current
NEC 430.22 requires motor branch-circuit conductors to have an ampacity of not less than 125% of the motor's full-load current rating.
Question 2: What device is required by NEC Article 430 to protect a motor from overheating under running conditions?
- Branch-circuit fuse
- Overload protection device (Correct answer)
- Ground-fault circuit interrupter
- Short-circuit breaker
Correct answer: Overload protection device
NEC 430.31 requires overload protection to protect motors, motor-control apparatus, and motor branch-circuit conductors from excessive heating due to motor overloads and failure to start.
Question 3: Which NEC article governs the installation of motors and motor controllers?
- Article 410
- Article 422
- Article 430 (Correct answer)
- Article 440
Correct answer: Article 430
NEC Article 430 covers motors, motor branch circuits, and motor controllers, including their installation requirements.
Question 4: When inspecting a motor disconnecting means, what is the minimum horsepower rating requirement for motors rated over 2 hp at 600V or less?
- The disconnect must be rated at least equal to the motor's hp (Correct answer)
- The disconnect must be rated at 115% of the motor's hp
- The disconnect must be rated at 125% of the motor's hp
- The disconnect must be rated at 150% of the motor's hp
Correct answer: The disconnect must be rated at least equal to the motor's hp
Per NEC 430.110, the disconnecting means for a motor must have a horsepower rating not less than the motor's rated horsepower.
Question 5: What is the maximum distance allowed between a motor disconnect and the motor controller, according to NEC 430.102?
- Within sight and within 50 feet
- Within sight from the controller (Correct answer)
- Within sight from the motor
- No distance limit is specified
Correct answer: Within sight from the controller
NEC 430.102(A) requires the disconnecting means to be in sight from the controller location, meaning visible and not more than 50 feet away.
Question 6: During an inspection of a motor installation, you find the overload relay set at 140% of the motor's full-load current. This is most likely acceptable for which type of motor?
- A standard Design B motor
- A wound-rotor motor
- A motor with a service factor of 1.15 or greater (Correct answer)
- A permanent split-capacitor motor
Correct answer: A motor with a service factor of 1.15 or greater
NEC 430.52 allows overload devices to be set up to 140% of full-load current for motors with a marked service factor of 1.15 or greater.
CEI CEI Motor & Motor Control Inspection 1
According to NEC Article 430, what is the minimum branch-circuit conductor ampacity for a single motor?