Thermal imaging is a non-contact technology that converts invisible infrared radiation, the heat energy every object naturally emits, into a visible image called a thermogram. It lets you see temperature differences across surfaces without touching anything, making it invaluable for electrical maintenance, building diagnostics, and predictive maintenance programmes. This guide explains how the technology works, what a thermogram shows, where it is used in practice, and what to look for in a thermal imaging camera.
What Is Thermal Imaging? The Core Principle
Thermal imaging is the process of detecting infrared (IR) radiation emitted by objects and translating those emissions into a visual image that maps surface temperature differences. Every object with a temperature above absolute zero (−273.15 °C) emits infrared radiation. The hotter the object, the more infrared energy it emits. This is a fundamental law of physics, described by the Stefan-Boltzmann relationship, and it applies equally to a high-voltage busbar, a brick wall, and a human hand.
Infrared radiation sits just below visible light on the electromagnetic spectrum, with wavelengths typically between about 0.7 µm and 14 µm. Our eyes cannot see it, but a thermal imaging camera can. The camera's sensor detects IR energy, measures its intensity pixel by pixel, and assigns each pixel a colour or shade corresponding to its apparent temperature. The result is a thermogram: a two-dimensional heat map of the scene.
What makes this powerful is that temperature anomalies, things that are hotter or colder than they should be, often point to underlying faults. A loose electrical connection generates excess heat. A missing section of building insulation lets warmth escape. A failing bearing on a motor runs hotter than its neighbours. None of these problems are visible to the naked eye until they cause damage or failure. Thermal imaging reveals them early, often long before a fault becomes critical.
How a Thermal Imaging Camera Works
A thermal imaging camera is not a conventional camera that records reflected light. It captures emitted infrared radiation using a specialised detector, an IR lens, and onboard processing electronics.
The detector
Most cameras used in industrial and electrical thermography use an uncooled microbolometer detector. This is an array of tiny sensors (typically vanadium oxide or amorphous silicon) whose electrical resistance changes when infrared radiation heats them. The detector does not need cryogenic cooling, which keeps the camera compact and affordable. Cooled detectors exist for scientific and military applications where extreme sensitivity is required, but for electrical, building, and industrial work, uncooled detectors are the standard.
The lens
Ordinary glass blocks most infrared wavelengths, so thermal camera lenses are made from materials like germanium, zinc selenide, or chalcogenide glass that are transparent to IR radiation. This is one reason thermal cameras cost more than conventional cameras; the optics are specialist.
Image processing
The camera's processor takes the raw temperature data from each pixel and applies a colour palette to create the thermogram. You can usually choose between several palettes. Iron (ironbow) is popular for electrical work because it gives an intuitive gradient from cool blues and purples through warm yellows to hot whites and reds. The camera also lets you set emissivity, reflected temperature, and distance parameters to improve measurement accuracy, topics we will cover shortly.
Leading manufacturers in this space include FLIR and Fluke, both of which produce cameras widely used in Irish electrical, industrial, and building applications. As authorised distributors for both brands, Powerpoint Engineering supplies, calibrates, and supports these instruments in Ireland. You can explore the capabilities of Fluke thermal imaging cameras for a closer look at what current models offer.
Reading a Thermogram: What the Image Tells You
A thermogram is a colour-coded map of apparent surface temperatures. Understanding what those colours mean, and what they do not mean, is the difference between useful diagnostics and misleading conclusions.
Colour palettes
Thermal cameras offer multiple palettes. Each has its strengths depending on the application:
|
Palette |
Appearance |
Best used for |
|
Iron (Ironbow) |
Dark purple/blue → yellow → white |
Electrical inspections, general maintenance; high contrast for hot spots |
|
Rainbow (Spectrum) |
Blue → green → yellow → red |
Building surveys, broad temperature ranges; visually intuitive for reports |
|
Greyscale |
Black → white |
Structural detail, identifying shapes; useful when overlaying on visual images |
|
High Contrast |
Black → vivid colour accents |
Isolating extreme temperatures against a neutral background |
Hot spots and cold spots
A hot spot is an area on the thermogram that appears significantly warmer than its surroundings or than a comparable reference point. In electrical work, a hot spot on a busbar connection might indicate a high-resistance joint caused by corrosion, insufficient torque, or mechanical loosening. A cold spot on a building facade might indicate missing insulation or an area of moisture ingress cooling the surface through evaporation.
Delta-T: the critical measurement
Experienced thermographers do not just note that something is warm. They measure the delta-T (ΔT), the temperature difference between the anomaly and a comparable reference point under similar load and environmental conditions. A ΔT of 5 °C on a lightly loaded connection might be minor. A ΔT of 40 °C on the same connection under full load is a serious fault that demands immediate attention. Without a meaningful delta-T, a temperature reading on its own tells you very little. Context is everything.
Emissivity and Why It Matters
Emissivity is the measure of how efficiently a surface emits infrared radiation compared to a perfect theoretical emitter (a "blackbody"). It is expressed as a value between 0 and 1. A surface with an emissivity of 0.95 emits 95% of the IR energy a blackbody would at the same temperature. Get the emissivity setting wrong, and your temperature reading will be wrong.
Most non-metallic surfaces, such as painted walls, rubber, plastic, and oxidised steel, have high emissivity (typically 0.85 to 0.95) and are straightforward to measure. Bare, polished, or shiny metals are the trouble. Polished aluminium can have an emissivity as low as 0.05, meaning the camera is mostly seeing reflected IR from surrounding objects rather than the surface's own emissions. The result? A misleadingly low temperature reading, or worse, a reflected hot spot from a nearby heat source that looks like the metal itself is overheating.
Practical workarounds include applying a strip of high-emissivity electrical tape to the target surface, adjusting the emissivity setting on the camera to match the material, and accounting for reflected apparent temperature. Any competent thermographer checks and records the emissivity setting used. Without this discipline, reports can be dangerously inaccurate.
Thermal Imaging in Electrical Maintenance
Electrical faults generate heat before they generate failures. That single fact is why thermal imaging has become one of the most widely used condition-monitoring tools in electrical maintenance worldwide. It is a non-contact method, so you can scan energised switchgear, distribution boards, transformers, motor control centres, and cable terminations without shutting anything down or exposing yourself to live conductors.
What faults can thermal imaging detect?
- Loose or corroded connections in LV and MV panels, causing localised overheating.
- Overloaded circuits, where conductors or busbars run hotter than their rated capacity.
- Unbalanced phases, visible as uneven temperature distribution across a three-phase supply.
- Failing fuses or contactors that show abnormal heat patterns.
- Transformer hot spots, indicating winding insulation degradation, poor oil circulation, or tap changer faults.
- Motor bearing and winding problems, where thermal patterns differ from baseline.
The key advantage is early detection. A connection running 30 °C above its reference might be months away from catastrophic failure, but it is already well on the road. Finding it now means a planned repair during a scheduled outage, not an unplanned trip, an arc-flash event, or a fire. For a deeper look at how thermal imaging fits into a broader predictive maintenance programme, including the cost and downtime savings it enables, see our dedicated guide.
Critically, thermal surveys on electrical equipment should be carried out while the system is under normal or near-full load. Scanning an unloaded panel is largely pointless; faults reveal themselves through heat generated by current flow. This means the survey must be planned around operational schedules.
Building and Energy Efficiency Applications
Thermal imaging is equally valuable outside the electrical panel. For building fabric diagnostics, a thermal camera can quickly identify:
- Missing or damaged insulation in walls, roofs, and floors, visible as cold patches on the inner surface or warm patches on the exterior during heating season.
- Air leakage around windows, doors, and service penetrations.
- Moisture ingress, where damp areas cool through evaporation and appear distinctly colder.
- Underfloor heating faults, where broken loops or blockages show as uneven heat distribution.
- Flat roof leaks, where retained moisture cools at a different rate to dry sections after sunset.
In Ireland, the Sustainable Energy Authority of Ireland (SEAI) promotes building energy efficiency upgrades, and thermal imaging provides concrete evidence of where heat is being lost. It is a fast, non-destructive way to prioritise retrofit work. For more on this topic, read our article on thermal imaging for affordable energy loss detection.
Other Industrial and Safety Applications
Beyond electrical and building work, thermal imaging has a remarkably wide range of uses across industry. Mechanical engineers use it to monitor bearing temperatures on rotating equipment, identify misaligned drives, and check steam traps (a failed-open steam trap wastes enormous amounts of energy, and it shows up immediately on a thermogram). Process industries use it to inspect refractory linings in furnaces and kilns, detecting thin spots before they cause burn-throughs.
In the renewables sector, thermal cameras mounted on drones inspect wind turbine blades for delamination, lightning strike damage, and adhesive bond failures. Powerpoint has written separately about inspecting wind turbines with thermal imaging.
Fire services and insurance surveyors use thermal imaging to locate hidden fires inside walls and ceilings, or to verify that a fire is fully extinguished before leaving the scene. In electrical safety, a thermal survey can form part of a broader condition assessment before maintenance, helping identify which panels or circuits warrant closer physical inspection.
Thermal Imaging vs Visual Inspection
A visual inspection tells you what the surface looks like. Thermal imaging tells you what is happening beneath or behind that surface, as long as it produces a temperature difference. These are complementary methods, not substitutes for one another.
Thermal imaging excels at finding problems that are invisible to the eye: a connection that looks perfectly fine but is 45 °C hotter than its neighbour; an area of wall that appears sound but is losing heat through a gap in the insulation. You simply cannot see infrared radiation, no matter how experienced you are.
But thermal imaging has real limitations that you need to understand:
- It measures surface temperature only. It cannot see through walls, doors, or enclosures. If the heat has not conducted to the outer surface, you will not see it.
- It requires a temperature difference. No load on the circuit means no current, no heat, and no detectable fault.
- Environmental conditions affect accuracy. Wind, rain, and direct sunlight can mask or distort thermal patterns on outdoor equipment and building facades.
- Low-emissivity and reflective surfaces can produce misleading readings if emissivity is not properly accounted for.
For these reasons, best practice combines thermal imaging with physical inspection, electrical testing (insulation resistance, partial discharge), and other condition-monitoring techniques such as vibration analysis or oil analysis, depending on the asset.
Standards, Qualifications, and Best Practice
Thermal imaging surveys should be carried out by personnel who are trained and, ideally, certified to a recognised standard. The international benchmark for thermographer competence is ISO 18436-7, which defines three certification levels (Category I, II, and III) with increasing scope of responsibility and analytical capability.
In practice, a Category I thermographer can collect data and identify anomalies, while a Category II thermographer can establish inspection procedures, set acceptance criteria, and interpret results in a broader maintenance context. Certification typically involves a combination of classroom training, practical assessment, and documented field experience.
From a regulatory perspective, the Health and Safety Authority (HSA) in Ireland does not mandate thermal imaging as a specific legal requirement, but its guidance on electrical safety at work and on the management of workplace hazards clearly supports the use of condition-monitoring techniques, including thermography, as part of a risk-based approach to maintenance. The principle is straightforward: if a non-contact, non-destructive method can detect a fault before it causes a fire, an arc flash, or an unplanned outage, you should be using it.
Key standards and references relevant to thermographic inspection include:
- ISO 18436-7, condition monitoring and diagnostics of machines, thermography.
- IEC 62446-3, thermographic inspection of photovoltaic systems (where applicable).
- EN 13187, qualitative detection of thermal irregularities in building envelopes.
Choosing a Thermal Imaging Camera
If you are selecting a thermal camera for electrical or industrial use, these are the specifications that matter most:
- Detector resolution: measured in pixels (e.g. 160 × 120, 320 × 240, 640 × 480). Higher resolution means you can identify smaller anomalies from a greater distance. For electrical panel inspections, 160 × 120 is adequate for basic screening; 320 × 240 or above is preferred for detailed diagnostics.
- Thermal sensitivity (NETD): expressed in millikelvins (mK). Lower is better. A camera with < 50 mK sensitivity can detect very small temperature differences.
- Temperature range: ensure it covers your expected measurement range. Most industrial cameras cover −20 °C to at least +350 °C; some extend to +650 °C or higher.
- Image storage and reporting: radiometric image storage (where every pixel retains its temperature data) allows post-survey analysis. Cameras with built-in reporting software or compatibility with desktop analysis tools save time.
- Ruggedness: an IP54 or higher rating, drop-tested housing, and a screen visible in bright daylight are practical necessities on Irish sites.
Powerpoint Engineering supplies and calibrates thermal cameras from both FLIR and Fluke. The FLIR E6 Ex-Series, for example, is a compact, cost-effective option suitable for electrical and mechanical inspection, with a point-and-shoot interface that gets new users up and running quickly.
FAQs
Can thermal imaging see through walls or solid objects?
No. Thermal imaging measures surface temperature only. It cannot see through solid materials. What it can do is detect temperature differences on the surface caused by conditions behind it, such as missing insulation, moisture, or a hot pipe, but it is not X-ray vision. The anomaly must produce a measurable thermal effect on the visible surface.
Do you need training to use a thermal imaging camera?
Pointing the camera and capturing an image is simple enough. Interpreting the results correctly requires training. Understanding emissivity, reflected temperature, load conditions, and delta-T measurements is essential if you want to avoid false positives and missed faults. Certification to ISO 18436-7 Category I or II is recommended for anyone producing inspection reports.
How often should electrical equipment be thermally inspected?
There is no single mandatory frequency in Irish regulations, but most maintenance programmes inspect critical switchgear and distribution boards annually. High-criticality assets, or equipment with a history of faults, may warrant six-monthly scans. The inspection interval should be based on risk, asset age, load profile, and environmental conditions.
Conclusion
Thermal imaging is a straightforward concept with profound practical value. Every object emits infrared energy proportional to its temperature, and a thermal camera makes that invisible energy visible. For electrical contractors, facilities engineers, and maintenance teams in Ireland, it is one of the most effective tools available for catching faults early, prioritising repairs, and preventing costly, dangerous failures.
Whether you need a thermal camera for your own team or a fully managed survey carried out by experienced thermographers, Powerpoint Engineering can help. Explore our thermal imaging and infrared cameras range, or contact us to discuss a thermal imaging survey for your site.