Thermal Foundations for Apprentices

Self-check: 15 questions

Every option is explained, right and wrong. The pass mark for this tier is 70%.

Awareness training only. This free course explains what a thermal image shows and how electricians use one. It does not qualify you to work on or near energized equipment, and it is not an infrared thermography certification. It has not been independently reviewed by an ASNT NDT Level III (IR). Your employer determines who is qualified for a task under NFPA 70E; follow your employer's safety program and your supervising electrician.

1. An infrared camera pointed at an electrical panel measures which of the following?

From: Lesson 1 — What thermal imaging is and why electricians use it
  • A. The current flowing in each conductor
    Wrong. The camera never measures current. Heating is caused by current through resistance, but the camera only sees the resulting surface temperature.
  • B. The surface temperature of what it can see Correct
    Correct. The camera reads infrared energy leaving surfaces in its field of view and reports surface temperature. Everything beyond that is interpretation.
  • C. The internal temperature of the breaker
    Wrong. Infrared does not see through a breaker case. An internal problem only shows up if enough heat reaches the outer surface.
  • D. The insulation resistance of the conductors
    Wrong. Insulation resistance is measured with an insulation resistance tester on de-energized equipment. Infrared measures no electrical property at all.
Reference: ANSI/ASNT CP-105-2024, IRT Level I topical outline: Infrared Physics

2. Why is comparing the three phases of the same circuit more useful than reading one temperature on its own?

From: Lesson 1 — What thermal imaging is and why electricians use it
  • A. Because the camera is more accurate on three-phase equipment
    Wrong. Camera accuracy does not depend on how many phases the equipment has.
  • B. Because ambient, emissivity and load are roughly equal across the three, so the difference isolates the fault Correct
    Correct. Identical phases share ambient, emissivity, distance, camera settings and usually load, so those variables largely cancel and the remaining difference points at the fault.
  • C. Because NFPA 70E requires a three-phase comparison
    Wrong. NFPA 70E governs electrical safety in the workplace, not infrared measurement technique.
  • D. Because a single reading is always inaccurate
    Wrong. A single reading is not always inaccurate, but on its own it lacks the context that makes it meaningful.
Reference: ASTM E1934, Standard Guide for Examining Electrical and Mechanical Equipment with Infrared Thermography

3. An apprentice is asked to remove the cover from an energized 480 volt motor control center so a scan can be taken. What is the correct response?

From: Lesson 2 — Safety around energized equipment
  • A. Remove it, since a scan has to be done under load
    Wrong. The scan does need load, but that does not authorise an unqualified person to expose energized parts.
  • B. Remove it only if wearing safety glasses
    Wrong. Safety glasses are nowhere near adequate for exposure inside an arc flash boundary on a 480 volt MCC.
  • C. Decline; removing covers on energized equipment is qualified-person work requiring a documented procedure and PPE Correct
    Correct. Removing covers on energized equipment exposes live parts, requires a qualified person, justification for energized work, the correct arc-rated PPE and a second person.
  • D. Remove it after switching the camera on
    Wrong. The camera has no bearing on the hazard. Turning it on changes nothing about the exposure.
Reference: NFPA 70E-2024, Article 130 (Work Involving Electrical Hazards)

4. Which boundary may an unqualified person cross only when escorted by a qualified person and advised of the hazard?

From: Lesson 2 — Safety around energized equipment
  • A. The arc flash boundary
    Wrong. The arc flash boundary concerns incident energy and burn injury, and is defined separately from the shock approach boundaries.
  • B. The limited approach boundary Correct
    Correct. The limited approach boundary is the outer shock boundary; an unqualified person may cross it only when escorted by a qualified person and advised of the hazard.
  • C. The restricted approach boundary
    Wrong. The restricted approach boundary may be crossed only by a qualified person, with an energized work permit and appropriate PPE.
  • D. The working space boundary
    Wrong. Working space is a clearance requirement for equipment installation, not an approach boundary around exposed energized parts.
Reference: NFPA 70E-2024, Article 130.4 (Approach Boundaries to Energized Electrical Conductors or Circuit Parts for Shock Protection)

5. What is the main safety advantage of an infrared window fitted to a panel door?

From: Lesson 2 — Safety around energized equipment
  • A. It increases the accuracy of the measurement
    Wrong. A window actually reduces the signal reaching the camera and requires a transmission correction, so it does not improve accuracy.
  • B. It allows the scan to be taken with the door closed, so no cover is removed and nobody enters the restricted approach boundary Correct
    Correct. The scan happens through the closed door under load, which removes the cover-removal hazard and keeps people out of the restricted approach boundary.
  • C. It removes the need for arc-rated clothing anywhere in the facility
    Wrong. PPE requirements are set by the task and the equipment label, and other tasks in the facility still carry their own exposure.
  • D. It allows an unqualified person to perform any scan unsupervised
    Wrong. A window reduces one hazard; it does not change who is qualified to perform and interpret an inspection.
Reference: NFPA 70E-2024, Article 130 (Work Involving Electrical Hazards)

6. A connection carries the same current as its two neighbours but runs much hotter. What has changed at that point?

From: Lesson 3 — Heat, temperature, and why a loose connection gets hot
  • A. The current has increased at that point only
    Wrong. The connections are in series with their loads; current is set by the circuit, not by the state of one joint.
  • B. The resistance at that point is higher Correct
    Correct. With current the same, higher resistance at that point produces more power dissipated there, by P = I squared times R.
  • C. The voltage at that point is higher
    Wrong. A poor connection produces a small voltage drop across itself, but it does not raise the system voltage at that point.
  • D. The ambient temperature at that point is higher
    Wrong. All three connections sit in the same enclosure sharing the same ambient air.
Reference: ANSI/ASNT CP-105-2024, IRT Level I topical outline: Heat Transfer

7. The current through a resistive connection doubles. Approximately how much does the heat generated at that connection change?

From: Lesson 3 — Heat, temperature, and why a loose connection gets hot
  • A. It stays the same
    Wrong. Heating depends strongly on current; it cannot be unchanged when current doubles.
  • B. It doubles
    Wrong. This assumes heating is proportional to current. The relationship is proportional to current squared.
  • C. It increases about four times Correct
    Correct. P = I squared times R, so doubling the current multiplies the heating by about four, assuming resistance is unchanged.
  • D. It halves
    Wrong. Heating rises with current, it does not fall.
Reference: ANSI/ASNT CP-105-2024, IRT Level I topical outline: Heat Transfer

8. Changing the palette on a thermal image from ironbow to grayscale has what effect on the measured temperatures?

From: Lesson 4 — Reading a thermal image
  • A. It lowers them
    Wrong. A palette is a display mapping only; it changes no underlying value.
  • B. It raises them
    Wrong. For the same reason, a palette cannot raise a measured value.
  • C. It has no effect on them Correct
    Correct. The palette maps temperature to colour for display. The radiometric data beneath is unchanged, which is why a report quotes measured values rather than appearance.
  • D. It averages them across the image
    Wrong. Averaging is a function of focus, distance and spot size, not of the colour scheme.
Reference: ANSI/ASNT CP-105-2024, IRT Level I topical outline: Equipment

9. A panel image appears almost entirely one flat colour with no detail. Which adjustment is most likely to reveal a fault?

From: Lesson 4 — Reading a thermal image
  • A. Widen the span
    Wrong. Widening the span spreads the colours over an even larger range and flattens the image further.
  • B. Narrow the span and centre the level on the temperatures present Correct
    Correct. Narrowing the span and centring the level places the colour range over the temperatures actually present, so small differences become visible.
  • C. Change to a rainbow palette and report what appears
    Wrong. A palette change alters appearance only, and choosing a palette to make an image look more alarming is not an honest basis for a finding.
  • D. Move further from the panel
    Wrong. Greater distance makes the target fill less of the measurement spot, which averages the reading and understates a hot spot.
Reference: ANSI/ASNT CP-105-2024, IRT Level I topical outline: Equipment

10. Why does an out-of-focus thermal image matter for measurement, not just appearance?

From: Lesson 4 — Reading a thermal image
  • A. It does not matter; focus only affects how the image looks
    Wrong. Focus affects the measurement itself, which is why it is checked before any reading is recorded.
  • B. The camera averages energy across the blurred area and can report a peak lower than the true value Correct
    Correct. A blurred target spreads its energy across neighbouring detector elements, so the hottest point is averaged with cooler surroundings and reads low.
  • C. It causes the camera to lose its calibration
    Wrong. Calibration is a property of the instrument and is not disturbed by focusing.
  • D. It changes the emissivity of the target
    Wrong. Emissivity is a property of the target surface and does not change with camera focus.
Reference: ASTM E1934, Standard Guide for Examining Electrical and Mechanical Equipment with Infrared Thermography

11. A three-phase feeder shows all three conductors uniformly warm along their entire length, with no concentrated hot spot. This pattern most suggests:

From: Lesson 5 — Common electrical problems seen in infrared
  • A. A loose connection
    Wrong. A loose connection concentrates heat at the termination, with the conductor behind it near normal.
  • B. An overloaded circuit Correct
    Correct. Resistance is distributed along the conductor, so excess current heats the whole run evenly. Confirm against the conductor rating with a clamp meter before reporting.
  • C. An open fuse
    Wrong. An open fuse removes current from that phase, which shows as a cold phase rather than uniform warmth.
  • D. A failed breaker case
    Wrong. A breaker problem produces heat at the breaker, not uniformly along the full length of all three conductors.
Reference: ASTM E1934, Standard Guide for Examining Electrical and Mechanical Equipment with Infrared Thermography

12. On a three-phase motor circuit, one phase reads noticeably cooler than the other two. What should the apprentice do?

From: Lesson 5 — Common electrical problems seen in infrared
  • A. Ignore it; only hot spots are findings
    Wrong. Scanning only for bright spots is one of the most common beginner errors; a cold phase can be the more serious finding.
  • B. Record it and report it, because a cold phase can mean that phase is not carrying current Correct
    Correct. A cold phase suggests it is not carrying current, from an open fuse, a failed contact or a dropped phase. Single-phasing will destroy a motor.
  • C. Increase the span until the phase looks warm
    Wrong. Adjusting the display to hide a difference is falsifying the observation.
  • D. Mark the circuit as passed, since nothing is overheating
    Wrong. Absence of heat is not evidence of a healthy circuit when the phase should be loaded.
Reference: ASTM E1934, Standard Guide for Examining Electrical and Mechanical Equipment with Infrared Thermography

13. A scan is requested on a circuit that is currently switched off and carrying no load. What is the correct response?

From: Lesson 5 — Common electrical problems seen in infrared
  • A. Scan it; results are the same either way
    Wrong. Without current there is no I squared R heating, so a connection fault produces no thermal signature.
  • B. Scan it, because an unloaded circuit is safer to inspect
    Wrong. It is safer, but it yields no useful information about resistive faults, so the inspection does not achieve its purpose.
  • C. Explain that the scan needs normal load, because with no current there is no resistive heating to reveal a fault Correct
    Correct. Resistive heating requires current. Inspections are performed under normal or near-normal load, which is why scans are scheduled around production.
  • D. Scan it and double every reading to compensate
    Wrong. Readings cannot be scaled to compensate for an absent fault signature; that would be fabricating data.
Reference: ASTM E1934, Standard Guide for Examining Electrical and Mechanical Equipment with Infrared Thermography

14. Under SNT-TC-1A, who certifies an individual as a Level I, II or III in a nondestructive testing method?

From: Lesson 6 — Where this goes: the career path
  • A. The training provider that delivered the course
    Wrong. A training provider supplies training and may administer examinations, but it does not certify the individual.
  • B. The employer, against its own written practice Correct
    Correct. SNT-TC-1A describes an employer-based scheme: the employer writes a written practice and certifies its own personnel against it.
  • C. The camera manufacturer
    Wrong. Equipment manufacturers sell and may train on instruments; they have no role in personnel certification.
  • D. The state electrical licensing board
    Wrong. Electrical licensing boards license electrical work; they do not administer nondestructive testing personnel certification.
Reference: ASNT SNT-TC-1A, Recommended Practice for Personnel Qualification and Certification in Nondestructive Testing

15. Which statement about the Voltmark VET-1 course is accurate?

From: Lesson 6 — Where this goes: the career path
  • A. It costs $995, runs 36 contact hours, and has no prerequisite Correct
    Correct. VET-1 is priced at $995, carries 36 contact hours, and lists no prerequisite. TF-0 is useful preparation but is not required.
  • B. It costs $995 and requires completion of TF-0 first
    Wrong on the prerequisite. TF-0 is free preparation and is not a requirement for enrolling in VET-1.
  • C. It is free and runs 4 contact hours
    Wrong. Those are the figures for TF-0, the free apprentice tier, not for VET-1.
  • D. It certifies the student directly, with no employer involvement
    Wrong. Voltmark issues a training and examination record; the employer certifies the individual under its written practice.
Reference: Voltmark Thermography Academy catalog, content/thermography/catalog.json
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Voltmark Thermography Academy is Voltmark's own training program. It is not ASNT certification and it is not affiliated with, endorsed by, or sponsored by ASNT, NFPA, ICC, or any certifying body or licensing authority. Certificates issued by this program attest to completing Voltmark training and passing Voltmark examinations. Employer qualification under NFPA 70E and any written practice remains the employer's responsibility. Always follow your employer's safety program and your supervising electrician.