Infrared Thermography

A couple of thoughts...

Does exposed copper stays factory shiny for very long - especially if overheated?

Would the heat from hot spots be likely to spread to adjacent surfaces (e.g. circuit breaker cases around the terminals or insulated wires) with lower emissivity values?

   - Andy.

Excellent questions — and very relevant in real field conditions.

On the first point: exposed copper rarely stays “factory shiny” for long.

Oxidation, dust, ageing, and especially overheating will quickly change the surface condition. This generally increases emissivity, but in a non-uniform and unpredictable way, which makes accurate IR measurement still difficult.

Regarding heat spreading: yes, thermal conduction will often transfer heat to adjacent components such as breaker terminals, insulation, or cable lugs. Many of these materials (plastics, painted metals, insulation) have much higher emissivity than bare copper, so they may show clearer thermal patterns.

However, this can also be misleading: the hottest visible surface may not be the true origin of the defect, just the area where heat is easier to “see”.

That’s why good thermography always combines:

emissivity awareness

understanding of heat transfer paths

and electrical context (load, torque, contact resistance)

Thermal imaging is powerful — but interpretation is as important as the camera itself.

Confusion indeed, I recall some years ago being shown an image of an 'overheating' switch box where the splodge of warmth was strangely close to part of a human outline - the operator was just looking at part of his own reflection !

Part of the problem is that a lot of finishes (including some paint finishes that look dark and matt) are in fact quite  reflective at the 10um or so wavelength, of the thermal camera and this has no safe relationship to the colour or otherwise in the visible spectrum (0.4 to 0.6 um wavelength.)

The other problem is being sure of any scaling of the false colour scale in the image to something sensible. Just cos its red, .just mean its the warmest thing, knowing if its 30C or 130 makes a big difference to what happens next.

If it gets to the point of sticking something on specially, then as well as tape, the temperature indicating labels, either peak reading irreversible or just instant temperature  are both very useful.

Mike

Great points Mike — reflections are probably one of the biggest traps in electrical thermography. I’ve seen similar cases where a “hot spot” was actually the operator or a nearby warm object reflected off a shiny enclosure or painted surface.

Totally agree as well: visible appearance (dark/matt) is not a reliable indicator of emissivity at ~10 µm, so relying on colour alone can lead to misleading conclusions.

And yes, the false-colour palette only shows “relative hottest in frame” unless the temperature scale/span is checked. A red area at 30°C vs 130°C drives completely different actions and urgency.

Using a known high-emissivity target (tape) or temperature indicator labels is a very practical way to validate readings and avoid false alarms — especially around busbars, terminals and breaker connections.

Thanks for sharing, really useful reminder.

Great points Mike — reflections are probably one of the biggest traps in electrical thermography. I’ve seen similar cases where a “hot spot” was actually the operator or a nearby warm object reflected off a shiny enclosure or painted surface.

Totally agree as well: visible appearance (dark/matt) is not a reliable indicator of emissivity at ~10 µm, so relying on colour alone can lead to misleading conclusions.

And yes, the false-colour palette only shows “relative hottest in frame” unless the temperature scale/span is checked. A red area at 30°C vs 130°C drives completely different actions and urgency.

Using a known high-emissivity target (tape) or temperature indicator labels is a very practical way to validate readings and avoid false alarms — especially around busbars, terminals and breaker connections.

Thanks for sharing, really useful reminder.