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HVAC NEC 2023

HVAC Basic Electrical Practice Test 1

Free HVAC Basic Electrical Practice Test 1. 25 questions on fundamental electrical concepts including conductance (mho), battery DC output, ammeter current measurement, Ohm's Law, fuse sizing, resistance as current opposition, ohmmeter operation, capacitor parallel circuits, voltmeter readings, parallel circuit current, power factor, single-phase vs three-phase systems, HVAC run capacitors, GFCI protection, transformer turns ratios, kilowatt-horsepower conversion, voltage drop, NEC grounding, control circuits, and 24V HVAC controls.

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HVAC electrical exams cover electrical theory (Ohm's Law, circuits), transformers, single-phase and three-phase motors, control wiring, safety, and troubleshooting.

Requirements vary by state. HVAC technicians typically need EPA 608 certification and may need a separate electrical license for line voltage work.

Electrical fundamentals for HVAC: Ohm's Law -- V = I x R. Knowing any two values lets you calculate the third. Power formula -- P = V x I (watts = volts x amps). For resistive loads: P = I squared x R = V squared / R. Parallel circuits: voltage is the SAME across all branches; current DIVIDES. Series circuits: current is the SAME through all elements; voltage DIVIDES.

25

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45 min

Time

70%

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HVAC Basic Electrical Practice Test 1 — Question List

Question 1: Which of the following is the unit of conductance?

Ohm
Mho
Ampere
Volts

Question 2: Which of the following current does a battery produces?

Direct current
Alternating current

Question 3: In electrical system the ammeter is used to measure?

Current
Voltage
Resistance
Power

Question 4: If the resistance of the circuit is decreases keeping the voltage same, what happens to the current in the circuit?

Increases
Decreases
Remains same

Question 5: Which of the electrical quantities are used in sizing of electrical fuses?

Volt and amps
Volt and power
Current and power
Current and ohms

Question 6: The resistance in circuit is the indication of …………………

How much opposition to current flow
How much EMF applied to circuit
How many coulombs crossed at a point in one second
Electrical pressure in the circuit

Question 7: Which of the following measuring equipment uses its own power source?

Ohmmeter
Voltmeter
Ammeter
Watt meter

Question 8: If two capacitors are connected in parallel with one having 20 mfd and second one with 10 mfd. What is its equivalent capacitance?

30 mfd
6.6 mfd
10 mfd
20 mfd

Question 9: If a voltmeter connected across two terminals indicates the maximum reading, what does it mean?

The two terminals are shorted
The two terminals are opened
The two terminals are in series
The two terminals are in parallel

Question 10: In parallel circuit the current flow will be same.

True
False

Question 11: What is power factor (PF) in an AC electrical circuit, and what does a power factor of 0.8 mean for an HVAC motor?

Power factor of 0.8 means the motor is operating at 80% of its rated speed
Power factor = real power / apparent power; PF = 0.8 means only 80% of supplied power does useful work. HVAC induction motors are inductive loads with PF typically 0.8-0.9 at full load
Power factor only applies to DC circuits -- AC circuits in HVAC are always at unity (1.0) power factor
A power factor of 0.8 means the motor is drawing 20% more voltage than its nameplate rating

Question 12: Why are large HVAC compressors and air handlers typically powered by three-phase electricity rather than single-phase?

Three-phase is required by code for all HVAC equipment above 1 ton -- single-phase is prohibited for compressors
Three-phase motors are more efficient, produce smoother constant torque, are self-starting (no capacitors), and can deliver more power with less current than equivalent single-phase motors -- ideal for large compressors and air handlers
Three-phase and single-phase motors are equally efficient -- three-phase is only chosen because it is cheaper to wire
Large HVAC compressors use three-phase because single-phase power does not produce enough voltage for compressor starting

Question 13: What is the function of a run capacitor in a single-phase HVAC motor, and what are symptoms of a failed run capacitor?

A run capacitor stores energy during starting and disconnects once the motor reaches full speed
A run capacitor creates a phase shift between main and auxiliary winding currents, maintaining a rotating magnetic field during operation. Failure causes the motor to run hot, draw excessive current, or fail to start
Run capacitors provide overcurrent protection for the motor winding -- they disconnect the motor if current exceeds rated amperage
A run capacitor is only used in three-phase motors to improve power factor -- single-phase motors do not use capacitors

Question 14: What is a GFCI (Ground Fault Circuit Interrupter) and where does the NEC require GFCI protection for HVAC equipment?

GFCI protection is only required for pools and hot tubs -- HVAC equipment is exempt because it operates at higher voltages
A GFCI detects current imbalance between hot and neutral (as small as 4-6 mA ground fault) and trips within 25ms, protecting against electrocution. NEC 210.8 requires GFCI for outdoor, garage, crawl space, and unfinished basement HVAC receptacles
GFCIs protect against overcurrent -- they replace fuses and circuit breakers in HVAC equipment panels
GFCI is only required for 120V equipment -- 240V HVAC equipment does not need ground fault protection

Question 15: A step-down transformer for an HVAC control circuit has a primary of 240 turns and secondary of 20 turns. If primary voltage is 240V, what is the secondary voltage?

Secondary voltage = 120 volts (transformer always steps voltage up when used in HVAC applications)
Secondary voltage = (N_secondary / N_primary) x V_primary = (20 / 240) x 240 = 20 volts. Transformer turns ratio directly determines voltage ratio
Secondary voltage = 480 volts (step-up transformers are used in HVAC to provide higher voltage for compressors)
Secondary voltage cannot be determined from turns ratio alone -- it depends on the current drawn by the load

Question 16: What is the conversion factor between horsepower (HP) and kilowatts (kW), and how many watts does a 3-HP compressor motor consume at full load (assume 100% efficiency)?

1 HP = 1,000 watts; a 3-HP motor consumes exactly 3,000 watts at full load
1 HP = 746 watts; a 3-HP motor outputs 2,238 watts. At 90% motor efficiency, actual input is about 2,487 watts (2.49 kW)
1 HP = 100 watts; a 3-HP motor only draws 300 watts because modern motors are very efficient
Horsepower and kilowatts cannot be directly compared because HP is a mechanical unit and kW is an electrical unit

Question 17: What is "voltage drop" in an HVAC branch circuit, and what does the NEC recommend as maximum voltage drop for branch circuits?

Voltage drop is only a problem in DC circuits -- AC HVAC circuits do not experience voltage drop
Voltage drop (V = I x R) reduces voltage at HVAC equipment. NEC recommends maximum 3% for branch circuits and 5% total. Excessive drop causes motors to run hot, draw high current, and fail prematurely
The NEC requires a maximum of 10% voltage drop for all HVAC branch circuits
Voltage drop increases voltage at the equipment because the wire acts as a step-up transformer for long runs

Question 18: What is the purpose of equipment grounding in HVAC systems, and how does it differ from system grounding (neutral grounding)?

Equipment grounding provides a current-carrying path for normal HVAC operation -- without it the equipment will not run
Equipment grounding connects non-current-carrying metal parts to the grounding system; fault current returns via the EGC to trip overcurrent protection rather than flowing through a person contacting the equipment
Equipment grounding is the same as system grounding -- both serve the same purpose and the terms are interchangeable
Equipment grounding is only required for three-phase HVAC systems -- single-phase residential systems are exempt

Question 19: In an HVAC system, what is the purpose of the 24V AC control circuit, and what terminal designations are used on the thermostat wiring?

The 24V control circuit carries the main power supply to the compressor motor and blower motor
The 24V circuit is a low-voltage control circuit from a step-down transformer; thermostat wiring signals (Y=cooling, W=heating, G=fan, O/B=reversing valve) control contactors and relays by switching this 24V signal to the appropriate equipment
24V control circuits are only found in residential HVAC -- commercial systems always use 120V control circuits
The C (common) terminal provides 24V power to the thermostat -- R is the return path to the transformer

Question 20: What is the difference between a circuit breaker and a fuse for overcurrent protection, and how does each operate?

Fuses and circuit breakers are identical -- the only difference is the physical form factor (plug vs. panel mount)
A fuse is a one-time element that melts to open the circuit; a circuit breaker uses a bimetallic strip and electromagnet and can be reset after a fault. Both protect against overcurrent, but breakers are reusable. HVAC compressor circuits require time-delay (dual-element) fuses per NEC 440
Circuit breakers provide faster protection than fuses and should always be used instead of fuses in HVAC systems
Fuses only protect against voltage surges -- circuit breakers protect against overcurrent in HVAC systems

Question 21: What does "RMS voltage" mean, and why do we use 120V RMS instead of the peak voltage when describing household AC power?

RMS voltage is the highest voltage reached during an AC cycle -- 120V RMS means the voltage peaks at 120V
RMS voltage is the equivalent DC value producing the same heating effect. For a sine wave: V_peak = V_RMS x 1.414 (so 120V RMS peaks at 169.7V). Using RMS makes AC power calculations the same as DC calculations
RMS stands for Rotating Magnetic Strength -- it describes the rotating magnetic field in a three-phase motor
120V RMS and 120V DC produce different heating effects in a resistor -- RMS is only used for theoretical calculations

Question 22: In a 208V/120V three-phase wye (Y) system, what is the relationship between line voltage (208V) and phase voltage (120V)?

In a 208V/120V system, line voltage (208V) is exactly double the phase voltage (120V)
Line voltage = phase voltage x 1.732 (square root of 3). In 208V/120V wye: 120V x 1.732 = 208V. Phase voltage is line-to-neutral; line voltage is line-to-line
Line voltage and phase voltage are identical in a wye system -- 208V and 120V are two different systems in the same building
In a three-phase system, line voltage is always half of phase voltage because current splits three ways

Question 23: What does MCA (Minimum Circuit Ampacity) and MOP (Maximum Overcurrent Protection) mean on an HVAC equipment nameplate?

MCA is the maximum current the equipment draws at starting; MOP is the current at which the equipment automatically shuts off to prevent overheating
MCA is the minimum wire ampacity required for the branch circuit (sized to carry continuous running current); MOP is the maximum fuse or breaker size allowed. Both are on the HVAC nameplate per NEC 440.4
MCA and MOP are the same value -- they both indicate the minimum fuse size required for the equipment
MCA means Minimum Cooling Ampacity -- the current draw at minimum cooling load for energy calculations

Question 24: How does a contactor work in an HVAC system, and why is a contactor used instead of a relay to control a compressor?

A contactor is a type of capacitor that stores energy and releases it to start the compressor
A contactor is an electromagnetically-operated switch: 24V coil energizes and pulls in the armature to close heavy-duty main contacts that carry compressor motor current. Contactors are used (not relays) because they handle high motor current and starting inrush
Contactors are only used in three-phase systems -- single-phase compressors use standard relays for switching
A contactor coil operates at 240V line voltage -- the main contacts carry the 24V control signals to the thermostat

Question 25: What is an AFCI (Arc Fault Circuit Interrupter) and is it required for HVAC branch circuits in dwellings?

AFCI breakers are required for all HVAC circuits because compressor starting arcs always trigger the AFCI protection
AFCIs detect high-frequency arcing fault signatures to prevent arc-initiated fires. NEC 210.12 requires AFCI for 120V dwelling branch circuits; 240V HVAC compressor circuits are generally not covered by the dwelling AFCI requirement (verify with local AHJ)
AFCIs and GFCIs are the same device -- they detect the same type of fault using different names in different regions
AFCI protection is prohibited for HVAC branch circuits because HVAC motors generate arcing signatures during normal starting that would cause nuisance trips

Key NEC References for This Test

Article	What It Covers
Art. 440	Air Conditioning Equipment — use nameplate MCA and MOCP, not FLA alone
Art. 430	Motors — general motor rules that Art. 440 modifies

Study Tip: Practice reading ladder diagrams. Trace each rung from L1 to the load: contacts open → circuit dead. Contacts closed → current flows. This is how HVAC electrical troubleshooting works.

EXAM CARD HVAC

Questions25

Time limit45 min

Pass score70%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 Art. 440 & electrical theory