TN LLE HVAC and Air-Conditioning Circuits — Questions and Answers
Question 1: According to NEC Article 440, what is the maximum allowable voltage drop for the branch circuit supplying an air-conditioning compressor?
- 3%
- 5%
- No specific limit in Article 440 (Correct answer)
- 10%
Correct 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.
While the NEC provides voltage drop recommendations in informational notes (suggesting 3% for branch circuits and 5% total), Article 440 specifically governing air-conditioning and refrigeration equipment does not mandate a specific voltage drop limit. The voltage drop recommendations are advisory rather than enforceable requirements.
Question 2: What determines the minimum branch-circuit conductor size for a single hermetic refrigerant motor-compressor per NEC 440.32?
- The nameplate rated-load current (Correct answer)
- 125% of the rated-load current
- The nameplate minimum circuit ampacity
- 115% of the locked-rotor current
Correct 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.
NEC 440.32 states that conductors supplying a single motor-compressor shall have an ampacity not less than 125% of either the rated-load current or the branch-circuit selection current, whichever is greater. The rated-load current is the primary value found on the equipment nameplate and serves as the basis for conductor sizing calculations.
Question 3: When an air-conditioning unit has both a compressor motor and a fan motor, how is the overcurrent protection device sized?
- Based on the largest motor only
- Sum of all motor currents plus 25%
- 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 (Correct answer)
- Based on the locked-rotor current of all motors combined
Correct 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.
For multimotor equipment like an A/C unit with compressor and fan motors, NEC 440.22 requires the overcurrent device to be rated based on the compressor motor's applicable table value (which accounts for starting current) plus the full-load current ratings of the additional motors. This ensures the OCPD can handle the highest starting surge while protecting against overload.
Question 4: What is the maximum distance a disconnecting means for an air-conditioning unit can be located from the equipment per NEC 440.14?
- Within 25 feet
- Within 50 feet
- Within sight from and readily accessible (Correct answer)
- Adjacent to the unit only
Correct 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.
NEC 440.14 specifies that the disconnecting means shall be located within sight from and readily accessible from the air-conditioning or refrigerating equipment. 'Within sight' is defined by the NEC as visible and not more than 50 feet distant. This ensures maintenance personnel can verify the disconnect is open while working on the equipment.
Question 5: 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)?
- 50%
- 80% (Correct answer)
- 100% if no other outlets exist
- 60%
Correct 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.
NEC 440.62(B) limits a cord-and-plug-connected room air conditioner to 80% of the branch-circuit rating when other outlets are supplied by the same circuit. If the air conditioner is the only load on the circuit, it may be rated up to 50% of the branch-circuit rating for a 15A or 20A circuit. This ensures adequate capacity for other connected loads.
Question 6: Per NEC 440.65, what additional protection is required for single-phase residential HVAC equipment rated at 250 volts or less?
- Surge protection
- AFCI protection
- HACR-type circuit breaker
- Listed LCDI or AFCI protection cord set (Correct answer)
Correct 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.
NEC 440.65 mandates that single-phase cord-and-plug-connected room air conditioners, household refrigerators/freezers rated 250V or less shall be provided with a factory-installed LCDI (leakage-current detection and interruption) or AFCI protection device. This addresses the fire risk from damaged cords that can develop series arcing faults.
Question 7: When sizing conductors for a multi-motor HVAC unit, which NEC article works in conjunction with Article 440 for the non-compressor motors?
- Article 408
- Article 430 (Correct answer)
- Article 424
- Article 422
Correct 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.
NEC Article 440 specifically governs hermetic refrigerant motor-compressors, but HVAC equipment often includes fan motors, pump motors, and other auxiliary motors that fall under Article 430's general motor provisions. When calculating conductor sizing and overcurrent protection for multimotor HVAC equipment, both articles must be applied — Article 440 for the compressor portion and Article 430 for all other motors.
Question 8: What type of short-circuit and ground-fault protection is typically required for a hermetic motor-compressor branch circuit?
- Standard inverse-time circuit breaker rated at 125% of RLA
- Fuses or HACR-type breaker not exceeding 175% of rated-load current (Correct answer)
- Any breaker rated at 100% of the locked-rotor current
- Time-delay fuses rated at 200% of FLA
Correct 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 440.22(A), the branch-circuit short-circuit and ground-fault protective device for a motor-compressor shall be rated not more than 175% of the motor-compressor rated-load current. If 175% does not correspond to a standard device rating, the next higher standard rating is permitted. Additionally, the equipment nameplate may specify maximum fuse size or HACR-type circuit breaker rating.
Question 9: Per NEC 440.12, what is the minimum number of disconnecting means permitted for an air-conditioning unit?
- One per motor
- Two — one for power, one for control
- One single disconnect for the entire unit (Correct answer)
- Three — compressor, fan, and control
Correct 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.
NEC 440.12 allows one disconnecting means to serve as the disconnect for the entire air-conditioning unit, including all motors and controllers. This single disconnect must open all ungrounded supply conductors simultaneously and have no pole that can operate independently. For multimotor equipment like a packaged HVAC unit, this simplifies the installation requirement.
Question 10: What is the minimum conductor ampacity required for a 20-ampere rated-load current hermetic compressor on its own branch circuit?
- 20 amperes
- 23 amperes
- 25 amperes (Correct answer)
- 30 amperes
Correct answer: 25 amperes
Per NEC 440.32, conductor ampacity must be at least 125% of the rated-load current. 125% x 20A = 25A.
NEC 440.32 requires that branch-circuit conductors supplying a single motor-compressor have an ampacity not less than 125% of the rated-load current (or branch-circuit selection current, whichever is greater). For a 20-ampere rated-load current: 20A x 1.25 = 25 amperes minimum conductor ampacity. This would typically require a 10 AWG copper conductor.
Question 11: According to Tennessee licensing requirements, can a Limited Licensed Electrician install a central air conditioning system in a new commercial building?
- Yes, without restrictions
- Yes, if the system is under 200 amperes
- No, this typically requires a full electrical contractor license (Correct answer)
- Yes, but only in buildings under 5,000 square feet
Correct 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.
The Tennessee Limited Licensed Electrician (LLE) license has specific scope limitations. Central air conditioning installations in new commercial buildings generally fall outside the LLE scope and require a fully licensed electrical contractor. The LLE license is primarily designed for residential work and certain limited commercial applications. Always verify current Tennessee Board of Licensing Contractors regulations for specific scope of work allowances.
Question 12: When installing a mini-split HVAC system, what is the NEC requirement for the outdoor unit's disconnecting means?
- No disconnect is required for units under 1 HP
- A disconnect within sight from the outdoor unit (Correct answer)
- Only a circuit breaker at the panel is required
- A disconnect inside the building near the indoor unit
Correct 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.
Mini-split outdoor units are classified as air-conditioning equipment under NEC Article 440 and must comply with Section 440.14, which requires a disconnecting means within sight from and readily accessible from the equipment. This typically means installing a non-fused or fused disconnect switch near the outdoor unit, even though the circuit breaker in the panel also serves as overcurrent protection. The disconnect must be readily accessible and within 50 feet with a direct line of sight.
TN LLE HVAC and Air-Conditioning Circuits
According to NEC Article 440, what is the maximum allowable voltage drop for the branch circuit supplying an air-conditioning compressor?
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