What Is a Thermal Camera? Resolution, NETD, Emissivity and Electrical Panel Inspection
How a thermal camera works, what resolution and NETD mean, emissivity settings, errors on shiny metal, spot size by distance and reading temperature rise in panel thermography.
A thermal camera detects the infrared radiation (8–14 µm) emitted by objects and turns each pixel into a temperature value. Without contact and without switching off, it reveals loose connections, overloaded circuits, thermal bridges and moisture. Detector resolution, thermal sensitivity (NETD), temperature range and field of view decide the choice; correct results depend on the emissivity setting.
> Related Category: Browse models by resolution and range in Thermal Cameras, and Infrared Thermometers for spot readings.
1. Resolution and NETD
Thermal resolution is the pixel count of the infrared detector, not the screen; every pixel is a separate temperature reading.
| Detector resolution | Measuring points | Use |
|---|---|---|
| 80 × 60 | 4,800 | Quick close-range checks, leak tracing |
| 160 × 120 | 19,200 | Entry level for panels, motors and buildings |
| 256 × 192 / 320 × 240 | 49,000–76,800 | Professional electrical and mechanical maintenance, reporting |
| 640 × 480 | 307,200 | Long range, small targets, substations, research |
NETD (thermal sensitivity) is the smallest temperature difference the camera resolves, in millikelvin (mK); lower is cleaner.
| NETD | Rating |
|---|---|
| ≤ 40 mK | Very good; suits building and moisture work |
| 50–60 mK | Good; enough for electrical and mechanical maintenance |
| ≥ 80–100 mK | Large temperature differences only |
Other nameplate values: temperature range (typically −20 to +550 °C), accuracy (usually ±2 °C or ±2%), refresh rate (9 Hz or 25–30 Hz) and field of view.
2. Spot size by distance (IFOV)
The area one pixel sees grows with distance. For a reliable reading the target must fill at least 3 × 3 pixels.
Example: with a 160 × 120 detector and a field of view of about 25°, one pixel covers 2.7 mm at 1 m, so the smallest reliably measured target is about 8 mm. From 3 m it becomes 25 mm; a small terminal screw blends with its surroundings and reads cooler than it is. Distant or small targets need higher resolution or a narrow lens.
3. What is emissivity and why does it matter?
Emissivity (ε) is a surface's ability to emit infrared radiation (0–1). The camera converts measured radiation to temperature using this value.
| Surface | Emissivity (approx.) |
|---|---|
| Electrical tape, painted surfaces, plastic insulation | 0.90–0.95 |
| Concrete, brick, wood | 0.90–0.95 |
| Oxidized copper or steel | 0.60–0.80 |
| Shiny aluminium | 0.04–0.10 |
| Shiny copper busbar | 0.03–0.07 |
- Shiny metal acts like a mirror: it shows reflections of the surroundings, so a very hot busbar can look cold.
- Remedy: apply black electrical tape or matt paint to the measuring point while de-energized, or measure an adjacent insulated or painted part.
- Set the camera's emissivity for the material; 0.95 suits most panel work.
- A thermal camera cannot measure through glass or acrylic covers; they block infrared. Open the inner door or use an infrared inspection window.
4. Thermal inspection of electrical panels
- Measure under load; the circuit should carry at least 40% load and have run for 30–60 minutes.
- Covers are opened by an authorized person at a safe distance with protective equipment.
- Focus carefully; a blurred image under-reads the hot spot.
- Compare the three phases side by side: a terminal clearly hotter than its neighbours at similar load marks the problem.
- Save thermal and visible images together; measure load current with a clamp meter and record it.
A common rating of the temperature difference (ΔT) between similar components at similar load:
| ΔT | Interpretation |
|---|---|
| 1–3 °C | Possible deficiency; monitor |
| 4–15 °C | Deficiency; repair at the next opportunity |
| > 15 °C | Serious deficiency; act immediately |
Typical findings: a loose terminal (hottest at the joint, fading along the cable), an overloaded circuit (evenly warm along the cable), unbalanced phases, and worn contacts in a breaker or contactor. For causes of loose joints see Terminal Block Types and Selection.
5. Building and mechanical use
- Insulation and thermal bridges: at least 10 °C difference between inside and outside is needed.
- Moisture and leaks: wet areas look cold through evaporation; underfloor heating pipes and hot water leaks show directly.
- Motors and bearings: a bearing hotter than on a neighbouring motor points to lubrication or alignment trouble.
- Solar panels: faulty cells and partial shading appear as hot spots; inspect in sunshine.
If a single point temperature is enough, an infrared thermometer is the more economical tool, but it gives no image and reads only where it is aimed.
Frequently asked questions
What is a thermal camera used for?
It shows surface temperatures as an image and finds loose connections and overloads in panels, heat loss and moisture in buildings, and friction or bearing faults in machines without contact.
What resolution is enough in a thermal camera?
160 × 120 is the entry level for panels and general maintenance. For reported professional work and small targets at 2–3 m, 256 × 192 or 320 × 240 is recommended.
What does NETD mean?
It is the smallest temperature difference the camera can resolve. A 50 mK camera shows a 0.05 °C difference; the lower the value, the more detailed the image.
Can a thermal camera see through walls?
No. It sees surface temperature only; a pipe or moisture in a wall shows only as far as it changes the surface temperature. It cannot see through glass either.
Why does a shiny copper busbar look cold?
Shiny metal has very low emissivity and reflects its surroundings. Apply electrical tape or matt paint, or measure a neighbouring high-emissivity part.