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HVAC NEC 2023

HVAC Certification Practice Test 5

This test covers three-phase power for HVAC equipment, including delta and wye configurations and phase rotation safety. You will practice identifying the dangers of reversed rotation on scroll compressors.

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HVAC Practice tests

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Frequently Asked Questions

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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.

Exam Tip: Remember that swapping any two of the three phase conductors reverses rotation, but swapping all three at once does not change rotation at all.

25

Questions

25 min

Time

70%

Pass

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HVAC Certification Practice Test 5 — Question List

Question 1: What is the phase offset between each of the three waveforms in a three-phase power system?

120 electrical degrees
90 electrical degrees
180 electrical degrees
60 electrical degrees

Question 2: Why doesn't a true three-phase induction motor need a start or run capacitor?

It runs on DC power instead of AC
The natural rotating magnetic field from the phase offset starts and runs the motor
It uses a centrifugal switch instead of a capacitor
It needs an extra transformer instead

Question 3: What best describes a delta configuration?

Windings joined at a common center point
A configuration used only for lighting circuits
A closed triangle connection with no inherent neutral point
A configuration that always requires four hot conductors

Question 4: What best describes a wye (star) configuration?

A closed triangle with no neutral
A configuration used only for single-phase power
A configuration that requires a run capacitor
Windings joined at a common point, which can be used to derive a neutral

Question 5: Which configuration is more common for motor-only loads that don't need a neutral conductor?

Delta
Wye
Single-phase
Split-phase

Question 6: Which configuration is common on distribution transformers that feed both three-phase equipment and single-phase 120V loads?

Delta
Wye
Open-delta only
Center-tap only

Question 7: How many hot conductors does a standard three-phase circuit typically use, not counting neutral or ground?

Two
Four
Three
One

Question 8: How do you reverse the rotation direction of a three-phase motor?

Swap the neutral and ground conductors
Increase the voltage on one phase only
Swap all three phase conductors at once
Swap any two of the three phase conductors

Question 9: A technician reconnects a three-phase scroll compressor after service. It powers up, runs, draws current, and makes noise, but the system shows no pressure rise. What is the most likely cause?

Reversed phase rotation causing the compressor to run backward
Low refrigerant charge
A failed run capacitor
A tripped high-pressure switch

Question 10: Why is it important to verify phase rotation with a meter before starting a newly wired three-phase compressor?

To check that the voltage is 24V
To prevent the compressor from running backward, which can cause rapid internal damage
To test for GFCI protection
To size the wire correctly

Question 11: What happens when a scroll compressor runs backward due to reversed phase rotation?

It runs normally, just louder than usual
It automatically reverses itself back after a few seconds
It draws current and makes noise but does not build proper pressure
It builds pressure faster than normal

Question 12: What tool should a technician use to confirm correct phase rotation before starting a three-phase compressor?

A clamp-on ammeter only
A capacitor tester
A thermometer
A phase rotation meter

Question 13: In a wye configuration, where does the neutral connection come from?

The common point where all three windings join
One of the three phase conductors
The equipment grounding conductor
A separate step-down transformer

Question 14: Which configuration is named for its closed triangle shape?

Delta
Wye
Star
Single-phase

Question 15: Does a three-phase induction motor need a starting device, like a centrifugal switch, the way single-phase motors do?

Yes, the same as a CSIR motor
Yes, the same as a PSC motor
No, because the rotating magnetic field starts the motor without extra components
Only in delta configurations

Question 16: A technician accidentally swaps two of the three phase conductors on a compressor terminal block during a repair. Before power is restored, what should be verified?

Only voltage needs to be checked
Nothing, since three-phase motors self-correct rotation
Only the ground connection needs to be checked
Phase rotation should be checked with a meter to confirm correct rotation before starting the compressor

Question 17: What is one key benefit of three-phase power for compressor motors compared to single-phase?

It provides a smoother, more constant rotating field without needing capacitors
It always runs at a lower voltage than single-phase
It eliminates the need for any overload protection
It works without any grounding

Question 18: A wye-connected distribution transformer can supply which combination of loads?

Only three-phase equipment, never single-phase
Both three-phase equipment and single-phase 120V loads, using the derived neutral
Only single-phase loads
Only DC loads

Question 19: Which statement is correct about delta configurations and neutral conductors?

A delta configuration always includes a built-in neutral
A delta configuration works only on DC power
A standard delta configuration has no inherent neutral point
A delta configuration cannot power motors

Question 20: A three-phase scroll compressor is running backward due to reversed phase rotation. What is a possible consequence if it keeps running?

No damage, since scroll compressors are direction-independent
Improved efficiency over normal operation
Automatic correction of rotation after a few minutes
Rapid internal damage from running in the wrong direction

Question 21: If a technician swaps all three phase conductors at once, instead of just two, what happens to the motor's rotation direction?

It stays the same, since swapping all three doesn't change the relative rotation
It reverses, just like swapping two conductors
The motor won't start at all
The motor runs at double speed

Question 22: A three-phase motor is rated to rotate clockwise when phases A-B-C are connected in that order to terminals T1-T2-T3. A technician connects them as C-B-A instead. What will happen?

The motor will run at the same speed and direction
The motor will rotate counterclockwise (reversed), since two conductors have effectively been swapped relative to the original order
The motor will not receive any power
The motor will run as if on single-phase power

Question 23: Why is verifying phase rotation especially important for scroll compressors?

Scroll compressors run on single-phase power only
Scroll compressors have no electrical components
Scroll compressors depend on rotation direction to build pressure, and can be damaged quickly if run backward
Rotation direction has no effect on scroll compressors

Question 24: What does a properly wired three-phase wye system provide that a delta system typically does not?

Higher voltage on all three phases
Automatic phase rotation correction
Built-in overload protection
A usable neutral point for single-phase loads

Question 25: A rooftop unit with a three-phase scroll compressor was just reconnected after a service call. Before starting the unit, what is the correct safety step regarding phase rotation?

Verify phase rotation is correct using a meter before starting the compressor
Start the unit and listen for unusual noise as verification
Check only the voltage between phases
Assume rotation is correct since the wiring looks the same as before

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 limit25 min

Pass score70%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

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Source: NEC 2026 Art. 440 & electrical theory