HVAC and Air-Conditioning Circuits Flashcards

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?

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.

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"?

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.

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?

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.

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?

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.

Which of the following is NOT a required marking on an air-conditioning unit's nameplate according to NEC 440.4?

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.

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?

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.