Free TN-LLE HVAC and Air-Conditioning Circuits Questions and Answers 1 — Questions and Answers
Question 1: A hermetic refrigerant motor-compressor has a rated-load current (RLC) of 20A. What is the minimum ampacity for the branch-circuit conductors supplying this motor-compressor?
- 20A
- 25A (Correct answer)
- 30A
- 23A
Correct answer: 25A
NEC 440.32 requires branch-circuit conductors supplying a single motor-compressor to have an ampacity of not less than 125% of the motor-compressor's rated-load current. Therefore, 20A multiplied by 1.25 equals 25A.
Question 2: According to NEC Article 440, a disconnecting means for an air-conditioning unit must be located within sight from the unit. What is the maximum distance to be considered "within sight"?
- 25 feet
- 50 feet (Correct answer)
- 75 feet
- 100 feet
Correct answer: 50 feet
The term "In Sight From" is defined in NEC Article 100 as being visible and not more than 50 feet distant from the other. This rule ensures a technician can safely de-energize the unit while working on it.
Question 3: An A/C unit's nameplate lists the rated-load current as 24A and specifies a "Maximum Fuse Size" of 40A. What is the maximum size inverse-time circuit breaker that can be used for branch-circuit protection?
- 30A
- 40A (Correct answer)
- 45A
- 50A
Correct answer: 40A
NEC 440.4(B) states that equipment shall be installed in accordance with the manufacturer's recommendations included in the listing or labeling. If the nameplate specifies a maximum fuse or HACR circuit breaker size, that value must not be exceeded.
Question 4: A 120-volt, cord-and-plug-connected room air conditioner is installed on a branch circuit that also supplies lighting outlets. What is the maximum permissible rated current of the air conditioner?
- 50% of the branch-circuit rating (Correct answer)
- 80% of the branch-circuit rating
- 100% of the branch-circuit rating
- 125% of the branch-circuit rating
Correct answer: 50% of the branch-circuit rating
According to NEC 440.62(C), where a cord-and-plug-connected room air conditioner is connected to a branch circuit that also supplies lighting units or other appliances, the total rated current of the air conditioner shall not exceed 50% of the branch-circuit rating.
Question 5: Which of the following is NOT a required marking on an air-conditioning unit's nameplate according to NEC 440.4?
- Manufacturer's name
- Rated-load current in amperes
- Phase and Voltage
- Recommended conductor size (Correct answer)
Correct answer: Recommended conductor size
NEC 440.4(A) lists required markings, including rated-load current, voltage, phase, and manufacturer's name. It does not mandate the recommended conductor size, as the electrician is responsible for calculating this based on the NEC.
Question 6: An air-conditioning unit has a rated-load current of 18A and a locked-rotor current of 90A. What is the minimum ampere rating for the required disconnecting means?
- 20A
- 25A
- 30A (Correct answer)
- 18A
Correct answer: 30A
As per NEC 440.12(A)(1), the disconnecting means must have an ampere rating of at least 115% of the motor-compressor's rated-load current. In this case, 18A * 1.15 = 20.7A. A standard 30A non-fused disconnect is the minimum standard size that meets this requirement.
Free TN-LLE HVAC and Air-Conditioning Circuits Questions and Answers 1
A hermetic refrigerant motor-compressor has a rated-load current (RLC) of 20A.
What is the minimum ampacity for the branch-circuit conductors supplying this motor-compressor?