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HVAC NEC 2023

HVAC Basic Electrical Practice Test 2

Free HVAC Basic Electrical Practice Test 2. 25 questions on transformer primary and secondary sides, inductance (henry), parallel resistor equivalent values, electromagnet strength, current path resistance, magnetic reluctance, DC meter AC conversion, series/shunt ohmmeter types, megger insulation testing, halogen leak detector sensitivity, Ohm's Law applications, wattmeter connection, clamp-on ammeter operation, Kirchhoff's Laws, AC reactance, power factor correction capacitors, motor overload relay function, three-phase power calculations, transformer VA rating, and ground fault protection.

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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 review -- Part 2: Inductance (henry, H) is the property of a coil that opposes changes in current by generating a back-EMF. Capacitance (farad, F) stores energy in an electric field and opposes changes in voltage. In AC circuits: inductors cause current to LAG voltage; capacitors cause current to LEAD voltage. Remember: "ELI the ICE man" -- E comes before I in an inductor (ELI), I comes before E in a capacitor (ICE).

25

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45 min

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HVAC Basic Electrical Practice Test 2 — Question List

Question 1: The input side of the transformer is termed as ……………………….

Primary side
Secondary side
High voltage side
Low voltage side

Question 2: What is the measuring unit of inductance?

Henry
Farad
Ohm
Mho

Question 3: If smallest resistance and higher resistance resistors are connected in parallel, what will be its equivalent resistance?

Less than smallest resistance resistor
Equal to smallest resistance resistor
Equal to highest resistance resistor
Higher than smallest resistance resistor and lesser than highest resistance resistor

Question 4: The strength of electronic magnet or coil conductor depends on the amount of ……………………

Current flow in the coil
Voltage applied to the coil
Power of the coil

Question 5: An electric current seeks the path of ……………..

Low resistance
High resistance
Low reluctance
High reluctance

Question 6: A magnetic field seeks the path of ………….

Low reluctance
High reluctance
Less resistance
High resistance

Question 7: A DC meter can be used to measure AC by inserting a ………………….. in series with meter movement?

Rectifier
Capacitor
Impedance
Inductor

Question 8: A meter which is used to measure low resistances is ……………..

Series ohmmeter
Shunt ohmmeter
Impedance meter
Combination of voltmeter and ammeter

Question 9: Which of the following is used to check insulation breakdown in motors and compressors?

Shunt ohmmeter
Multimeter
Megger
Capacitive volt meter

Question 10: A halogen leak detector can detect refrigerant leaks as small as …………….ounce per year

0.5
1
1.5
2

Question 11: An HVAC control circuit has a resistance of 48 ohms and a current of 0.5 amperes. What is the voltage across this circuit?

The voltage is 96 volts (V = I / R = 0.5 / 48 = incorrect application of Ohm's Law)
V = I x R = 0.5 A x 48 ohms = 24 volts -- the standard 24V HVAC control circuit voltage
The voltage is 4 volts (incorrect formula application)
The voltage cannot be determined from resistance and current alone -- voltage is independent of resistance

Question 12: How is a wattmeter connected in a circuit to measure real power, and what two elements does it sense?

A wattmeter is connected in parallel with both the current and voltage measurement points -- same as a voltmeter
A wattmeter has a current coil in SERIES with the load and a voltage coil in PARALLEL with the load; multiplying instantaneous V x I and averaging gives real power (watts), which accounts for power factor
A wattmeter is connected only in series with the load -- it measures current and calculates power from a preset voltage assumption
Wattmeters cannot be used in HVAC circuits because inductive motor loads produce variable wattage readings

Question 13: How does a clamp-on ammeter (CT clamp meter) measure current without disconnecting the circuit, and what is the difference between AC and DC clamp meters?

A clamp-on ammeter measures current by creating a direct electrical connection with the conductor through the clamp jaws
AC clamp meters use transformer action (changing flux from AC current induces voltage in secondary coil) without touching the conductor. DC clamp meters use Hall Effect sensors to detect the static magnetic field from DC current
Clamp meters measure voltage -- the clamp around the conductor converts voltage to a readable signal
Clamp meters can only be used on three-phase circuits -- single-phase measurements require breaking the circuit

Question 14: What is Kirchhoff's Current Law (KCL) and how does it apply to a junction point in an HVAC control circuit?

Kirchhoff's Current Law states that current always flows from negative to positive terminals in any circuit
KCL states that the sum of currents entering a junction equals the sum of currents leaving; in a parallel circuit this means total current equals the sum of individual branch currents
Kirchhoff's Current Law applies only to DC circuits -- AC circuits have current that reverses direction, violating KCL
KCL states that current is shared equally among all branches in a parallel circuit

Question 15: What is reactance in an AC circuit, and how do inductive reactance and capacitive reactance differ in their relationship to frequency?

Inductive and capacitive reactance are identical -- both increase with higher frequency in the same proportion
Inductive reactance (X_L = 2 pi f L) increases with frequency; capacitive reactance (X_C = 1/(2 pi f C)) decreases with frequency. Both are measured in ohms and do not dissipate power
Reactance only applies to DC circuits -- AC circuits use resistance (ohms) only
Inductive reactance decreases with higher frequency because inductors become more efficient at higher frequencies

Question 16: How do power factor correction capacitors work in commercial HVAC systems, and why are they installed at the utility service entrance or at motor terminals?

Power factor correction capacitors store energy that motors release during starting -- they are similar to start capacitors
PF correction capacitors supply leading reactive current that cancels motor lagging reactive current, raising power factor toward 1.0 and reducing total supply current -- lowering utility demand charges and conductor losses
Power factor correction capacitors replace run capacitors in HVAC motors when the power factor drops below 0.8
Power factor is automatically corrected by modern VFD drives -- capacitors are only needed for older equipment without VFDs

Question 17: What is a motor overload relay in an HVAC system, and how does it protect the motor winding from damage?

A motor overload relay protects the motor from voltage surges by disconnecting power when voltage exceeds rated value
A thermal overload relay contains bimetallic strips heated by motor current; sustained overcurrent bends the bimetal to trip contacts and stop the motor, protecting windings while allowing normal starting inrush current to pass without tripping
Motor overload relays replace fuses for short circuit protection -- they provide faster trip response than fuses
Overload relays only protect single-phase motors -- three-phase motors use phase loss protection instead

Question 18: What is the formula for calculating real power in a three-phase AC circuit, and what does the factor 1.732 represent?

Three-phase power = 3 x V_line x I_line x PF (the factor 3 because there are three phases)
Three-phase real power = 1.732 x V_line x I_line x PF. The 1.732 factor is the square root of 3, arising from the 120-degree phase relationship between the three voltages
Three-phase power formula is the same as single-phase -- just multiply single-phase power by 3 at the end
The 1.732 factor only applies to delta-connected motors -- wye-connected motors use P = V x I x PF directly

Question 19: What does the VA rating of an HVAC control transformer mean, and how do you determine the minimum VA needed for a control circuit?

VA rating is the same as watt rating -- a 40VA transformer delivers 40 watts of useful heating power to the control circuit
VA rating is the maximum apparent power the transformer can deliver; minimum VA = sum of all simultaneously energized control device VA ratings, plus 20-25% margin. Undersized transformer causes voltage sag and contactor chattering
VA rating indicates the transformer's input voltage range -- a 40VA transformer accepts 40-48V AC input
All HVAC control transformers have a fixed 40VA rating -- the installer does not need to calculate control load requirements

Question 20: What is the difference between a ground fault and an arc fault in an electrical circuit?

Ground faults and arc faults are the same -- both involve current flowing to ground through unintended paths
Ground fault = unintended current path to ground (GFCI detects at 4-6 mA). Arc fault = electrical discharge through degraded insulation (AFCI detects high-frequency signature). Both can cause fires but through different mechanisms
Arc faults always draw very high current (above 100A) -- they are easily detected by standard circuit breakers
Ground faults can only occur in residential wiring -- commercial HVAC systems are immune because they use grounded metal conduit

Question 21: What is the equivalent capacitance of two capacitors connected in series versus in parallel? Give an example using a 20 MFD and 30 MFD capacitor.

In series C_total = C1 + C2 = 50 MFD; in parallel 1/C = 1/C1 + 1/C2 = 12 MFD (same formula as resistors)
In PARALLEL: C_total = C1 + C2 = 50 MFD (capacitances add). In SERIES: 1/C = 1/C1 + 1/C2, so C = 12 MFD (less than smallest). Opposite of resistor rules: parallel resistors use reciprocal formula; parallel capacitors add
Capacitors in both series and parallel always give the same equivalent capacitance -- the arrangement does not matter
Two capacitors in series always give a capacitance equal to the larger of the two values

Question 22: What is phase loss (single phasing) in a three-phase HVAC motor, and why is it so destructive?

Phase loss only affects three-phase motors during starting -- once running, a motor operates normally on two phases indefinitely
Phase loss (one phase lost) causes the remaining two phases to carry 1.7-2x rated current; the motor overheats rapidly and can burn out within minutes without phase loss or electronic overload protection
Phase loss causes the motor to run faster than rated speed because there is less magnetic opposition
Three-phase motors automatically switch to single-phase operation when phase loss occurs, with no reduction in efficiency

Question 23: What is a solid-state relay (SSR) and what are its advantages over an electromechanical relay in HVAC control applications?

A solid-state relay uses a small electromechanical relay inside -- the "solid-state" refers to the enclosure material
An SSR switches using semiconductor devices (triacs/SCRs) instead of mechanical contacts; advantages include no moving parts, no contact wear, silent operation, extremely long life (100 million cycles), and fast zero-crossing switching
Solid-state relays are less reliable than mechanical relays because semiconductors degrade in high-temperature HVAC environments
SSRs are only used in low-voltage (24V) control circuits -- they cannot switch 120V or 240V loads

Question 24: Why must a run capacitor in an HVAC unit be discharged before testing or replacement, and what is the correct procedure?

Capacitors do not need to be discharged -- when AC power is removed the capacitor automatically discharges to zero within one cycle
Run capacitors store potentially lethal voltage (400-600V) after power removal. Discharge using a 20,000-ohm 5-watt resistor across the terminals for 3-5 seconds, then verify with a voltmeter. Never short with a screwdriver -- the arc is dangerous
Capacitors can be safely shorted with a metal screwdriver -- the brief spark is harmless and just releases the stored energy quickly
Only large 400V+ capacitors need discharge -- HVAC run capacitors rated at 370V AC store insufficient energy to cause injury

Question 25: Why are HVAC run capacitors rated 370V AC or 440V AC, and what happens if a 370V rated capacitor is used on a 480V circuit?

The voltage rating on a run capacitor is the starting voltage during compressor inrush -- 370V rating means the capacitor handles 370-volt starting surges
The voltage rating is the maximum RMS voltage the capacitor dielectric can withstand continuously. A 370V capacitor on 480V (679V peak) would experience catastrophic dielectric breakdown. Higher voltage ratings are always safe replacements; lower ratings are not
370V and 440V rated capacitors are interchangeable -- the voltage rating only indicates which color the leads should be for identification
Capacitor voltage rating has no effect on HVAC performance -- only the microfarad (MFD) value matters for motor operation

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