HVAC and Air-Conditioning Circuits Flashcards

According to NEC Article 440, what is the maximum allowable voltage drop for the branch circuit supplying an air-conditioning compressor?

Answer: No specific limit in Article 440

NEC Article 440 does not specify a maximum voltage drop for branch circuits supplying compressors. Voltage drop recommendations are found in informational notes throughout the NEC.

What determines the minimum branch-circuit conductor size for a single hermetic refrigerant motor-compressor per NEC 440.32?

Answer: The nameplate rated-load current

Per NEC 440.32, the branch-circuit conductor size for a single motor-compressor must not be less than 125% of the rated-load current OR the branch-circuit selection current, whichever is greater.

When an air-conditioning unit has both a compressor motor and a fan motor, how is the overcurrent protection device sized?

Answer: Based on the compressor rated-load current plus the full-load current of other motors, with OCPD sized per the largest motor's table value

The OCPD is sized using the largest motor's maximum rating from the applicable table, plus the sum of the rated-load or full-load currents of all other motors in the circuit.

What is the maximum distance a disconnecting means for an air-conditioning unit can be located from the equipment per NEC 440.14?

Answer: Within sight from and readily accessible

NEC 440.14 requires the disconnecting means to be within sight from and readily accessible from the air-conditioning or refrigerating equipment.

A room air conditioner connected to a 120-volt, 15-ampere branch circuit must not exceed what percentage of the circuit rating per NEC 440.62(B)?

Answer: 80%

Per NEC 440.62(B), a room air conditioner rated 120 volts shall not exceed 80% of the branch-circuit ampere rating if other outlets are also supplied.

Per NEC 440.65, what additional protection is required for single-phase residential HVAC equipment rated at 250 volts or less?

Answer: Listed LCDI or AFCI protection cord set

NEC 440.65 requires cord-and-plug-connected single-phase HVAC equipment rated 250 volts or less to be provided with one of several specified protection methods including LCDI or AFCI protection.

When sizing conductors for a multi-motor HVAC unit, which NEC article works in conjunction with Article 440 for the non-compressor motors?

Answer: Article 430

Article 430 covers motors in general and works alongside Article 440 for sizing conductors and protection for fan motors and other non-compressor motors in HVAC equipment.

What type of short-circuit and ground-fault protection is typically required for a hermetic motor-compressor branch circuit?

Answer: Fuses or HACR-type breaker not exceeding 175% of rated-load current

NEC 440.22(A) generally limits the OCPD to not exceed 175% of the rated-load current, though specific equipment nameplate values may allow different sizing.

Per NEC 440.12, what is the minimum number of disconnecting means permitted for an air-conditioning unit?

Answer: One single disconnect for the entire unit

NEC 440.12 permits a single disconnecting means for the entire unit, provided it disconnects all ungrounded supply conductors.

What is the minimum conductor ampacity required for a 20-ampere rated-load current hermetic compressor on its own branch circuit?

Answer: 25 amperes

Per NEC 440.32, conductor ampacity must be at least 125% of the rated-load current. 125% x 20A = 25A.

According to Tennessee licensing requirements, can a Limited Licensed Electrician install a central air conditioning system in a new commercial building?

Answer: No, this typically requires a full electrical contractor license

Tennessee's Limited Licensed Electrician scope is generally restricted to residential and small commercial work. Large commercial HVAC installations typically require a licensed electrical contractor.

When installing a mini-split HVAC system, what is the NEC requirement for the outdoor unit's disconnecting means?

Answer: A disconnect within sight from the outdoor unit

NEC 440.14 requires a disconnecting means within sight from and readily accessible from the equipment, which applies to mini-split outdoor units.