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HVAC NEC 2023

HVAC Certification Practice Test 14

This test covers megohmmeter (megger) insulation testing versus basic continuity checks, and how to diagnose grounded motor windings that a standard multimeter can miss.

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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: A winding can show normal resistance on a multimeter and still be grounded (shorted to the frame) — only an insulation test with a megger reveals that.

25

Questions

25 min

Time

70%

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HVAC Certification Practice Test 14 — Question List

Question 1: What does a megohmmeter (megger) primarily test on a motor?

The insulation resistance between the motor windings and the motor frame (ground)
The exact running speed of the motor
The capacitor's microfarad rating
The refrigerant charge level

Question 2: A motor winding shows normal resistance on a standard multimeter. Does this confirm the winding insulation is good?

Yes, normal resistance always confirms good insulation as well
No — a winding can show normal resistance and still be grounded (shorted to the frame)
Only three-phase motors can have this problem
Multimeters cannot measure motor windings at all

Question 3: What does it mean when a technician says a motor winding is "grounded"?

The winding's insulation has broken down, allowing current to leak from the winding to the motor frame
The motor is properly bonded to the equipment grounding conductor
The winding has too much resistance to operate
The motor has been intentionally grounded for safety

Question 4: Why does a megger apply a higher test voltage than a standard multimeter uses for resistance checks?

A higher voltage can reveal weak or marginal insulation that would not show a problem at normal low test voltages
Higher voltage makes the test faster only, with no accuracy benefit
It is simply a historical convention with no technical reason
Higher voltage is required to measure any resistance at all

Question 5: On a motor with healthy insulation, what would a megger reading between a winding and the frame generally look like?

A very low resistance value, close to zero
A very high resistance value, showing the insulation is effectively blocking current to ground
Exactly the same value every time regardless of insulation condition
A reading in amps rather than resistance

Question 6: A megger test shows a low resistance reading between a compressor winding and the compressor shell. What does this indicate?

The winding insulation has likely broken down and the winding is grounded to the shell
The compressor is running perfectly normally
The run capacitor needs to be replaced
The refrigerant charge is low

Question 7: A technician wants to confirm a motor winding is not open (broken). Which tool is appropriate for this specific check?

A standard multimeter's resistance or continuity function
Only a megger can check for an open winding
Neither tool can check for an open winding
A clamp-on ammeter is the correct tool for this

Question 8: A technician suspects a compressor is tripping a GFCI-protected circuit due to insulation breakdown. Which tool is best suited to confirm this?

A standard continuity buzzer only
A megohmmeter (megger)
A capacitor tester only
A pressure gauge set

Question 9: A compressor's three winding terminals all show expected resistance to each other on a multimeter, yet the compressor keeps tripping its breaker. What should the technician check next?

Insulation resistance from each winding to the compressor shell/ground with a megger
Nothing further is needed, the compressor must be fine
Only the run capacitor needs to be checked
Only the refrigerant charge needs to be checked

Question 10: Why should a technician disconnect a motor from its circuit and discharge related capacitors before performing a megger test?

To protect the meter and other components, and to get an accurate isolated reading of the motor alone
It is not actually necessary and is just an old habit
It only matters for single-phase motors
It is required only for motors under 1 horsepower

Question 11: What does a basic continuity/resistance check on a winding actually confirm?

That the winding is a complete, unbroken (not open) electrical path
That the winding insulation is definitely intact
That the compressor has the correct refrigerant charge
That the capacitor is within tolerance

Question 12: A multimeter shows infinite (OL) resistance between two winding terminals that should read a specific value. What does this indicate?

The winding is open (broken) — no continuous path exists
The winding insulation has failed to ground
The winding is perfectly normal
The capacitor is shorted

Question 13: A technician records megger readings on the same compressor over several service visits and notices the insulation resistance value has been dropping over time, though it is still passing. What does this trend suggest?

The insulation is gradually degrading and may fail completely in the future
This trend has no diagnostic value at all
It means the refrigerant charge is decreasing
It means the capacitor needs to be replaced

Question 14: How can moisture inside a motor affect a megger test result?

Moisture can lower the measured insulation resistance, sometimes falsely suggesting insulation failure
Moisture has no effect on megger readings whatsoever
Moisture always raises the reading artificially high
Moisture only affects three-phase motors

Question 15: True or False: A megger test also confirms the correct running speed and torque output of a motor.

True
False
Only true for single-phase motors
Only true above 5 horsepower

Question 16: On a three-phase motor, why does a technician often compare the resistance between all three winding pairs to each other, not just check that each is non-infinite?

A significant imbalance between the three readings can indicate a partial winding problem even if none reads fully open
The three readings are never expected to be similar
This comparison is only done on single-phase motors
It has no diagnostic value and is purely optional record-keeping

Question 17: Why might a technician megger-test a compressor that has been sitting idle in a flooded or damp mechanical room before restarting it?

To check whether moisture has compromised the winding insulation before applying power
To check the refrigerant charge level
To check the thermostat battery level
This test is never relevant after equipment has been idle

Question 18: On a healthy single-phase compressor, would a technician expect continuity directly between the run winding and the start winding terminals?

No, any connection between them always means a fault
Yes, they are typically connected internally through a common point
This only applies to three-phase motors
Windings are never connected to each other in any motor

Question 19: A megger test on a motor shows a high resistance reading well above the commonly accepted minimum acceptable level. What does this generally mean for that motor?

The insulation is in good condition at the time of the test
The motor is guaranteed to never fail again
The reading means the motor is definitely grounded
The reading has no useful meaning at all

Question 20: Why do thorough motor diagnostics often use both a continuity check AND a megger test rather than just one?

Together they check two different failure modes — an open winding and a grounded/shorted winding
The two tests are redundant and never give different information
Only the megger test is ever needed in practice
Only the continuity test is ever needed in practice

Question 21: A GFCI-protected outdoor disconnect keeps tripping whenever a specific condensing unit starts. Continuity checks on the compressor windings look normal. What should the technician check next?

Insulation resistance to ground with a megger, to check for a grounded winding
Nothing further, GFCI trips are unrelated to the compressor
Only the refrigerant charge needs checking
Only the thermostat wiring needs checking

Question 22: What general factors commonly contribute to motor winding insulation breaking down over time?

Heat, age, moisture, and electrical stress over the motor's service life
Insulation never degrades under any circumstances
Only refrigerant type affects insulation condition
Only the thermostat setting affects insulation condition

Question 23: Why is it useful to log megger readings over multiple service visits rather than only checking once when a motor fails?

Tracking the trend over time can reveal gradual degradation before an outright failure occurs
A single reading is always sufficient and trends have no value
Megger readings never change over a motor's life
Logging readings is only useful for warranty paperwork

Question 24: True or False: A passing megger reading means a technician never needs to visually inspect wiring and connections for other problems.

True
False
Only true for single-phase equipment
Only true if the reading is exceptionally high

Question 25: A compressor shows normal continuity between winding terminals but a low megger reading between a winding and the shell. What is the correct conclusion?

The compressor is completely healthy
The winding is not open, but the insulation has broken down — the winding is grounded
The winding is open and needs rewinding
The refrigerant charge is the actual problem

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